Astrophotography Complete Guide

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Hello My dear Friends,:have a nice day:

Astrophotography is one of the most beautiful & enjoyable activities in Astronomy (most in Amateur astronomy) and there are many astronomers who like it & work on it.

In this topic, we put some good & useful points about this subject from good resources like Sky at night magazine, Cloudy nights & ...

So be with us & share your comments here

*With special thanks to all those who have contributed their knowledge, hardware tips and softwares in the internet


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How to take nightscapes (http://forum.avastarco.com/forum/showthread.php?917-Astrophotography-Complete-Guide&p=29094&viewfull=1#post29094)
How to image the moon (http://forum.avastarco.com/forum/showthread.php?917-Astrophotography-Complete-Guide&p=29638&viewfull=1#post29638)
How to image the planets (http://forum.avastarco.com/forum/showthread.php?917-Astrophotography-Complete-Guide&p=30934&viewfull=1#post30934)
Imaging the Sun (http://forum.avastarco.com/forum/showthread.php?917-Astrophotography-Complete-Guide&p=31371&viewfull=1#post31371)
Something about your camera (http://forum.avastarco.com/forum/showthread.php?917-Astrophotography-Complete-Guide&p=31598&viewfull=1#post31598)
Introducing deep-sky photography (http://forum.avastarco.com/forum/showthread.php?917-Astrophotography-Complete-Guide&p=32599&viewfull=1#post32599)

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How to take nightscapes
From: Sky at night
There’s a huge range of subjects up there in the night sky just waiting to be captured with simple-to-use, inexpensive equipment. A camera and a tripod is all you need to start taking photos of fantastic ‘nightscapes’ – big, wide-field views of the heavens encompassing things like bright stars and the Moon, and perhaps set against a horizon.


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These types of shots are particularly good when that great sweep of stars that makes up our own Galaxy, the Milky Way, takes centre stage. Your pictures can also reveal the movement of the Earth by capturing star trails and tracking the changing positions of the planets over days, weeks and even months.

Closer to home there are meteor showers to watch out for, as well as ethereal noctilucent clouds and the shimmering greens and reds of the striking Aurora Borealis. All this and more can be captured with the most basic of equipment: a camera, a tripod and a remote shutter release.
Read on to find out how to do it.

.......to be continued

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Astrophotography is the photography of stars, planets, the Sun and Moon, and other celestial objects in the sky, such as galaxies, stars clusters and nebulae. It can be easy to get started shooting simple things but it will get progressively harder when you start to turn your attentions to the smaller, fainter objects.

“If you've never done this before try shooting the moon. You don;t have to do it in the middle of the night either you can get some beautiful shots at dusk,” said Jerry Lodriguss who's images of nebulae and galaxies have appeared in publications all over the world.

When it comes to equipment a simple camera and lens on a tripod will work or you can substitute the camera's lens for a telescope. A DSLR works best but you can use a compact with the cameras lens shooting through the eye piece of a telescope for shots of the moon or if you're feeling brave you can try a much more complex set-up: “Put a camera with a telescope substituting the camera lens on an equatorial mounting that is polar aligned with the Earth's rotational axis. Which is driven by a computer when using another telescope mounted piggyback on the prime telescope to track the stars with high accuracy.”
For those who live in towns and cities light pollution will stop you seeing the sky as it truly is so to get the best astrophotos you need to take a drive out into the country away from the city lights.


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EQUIPMENT

What you need to take your first quality astrophoto


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Many of us have a compact camera we use to take everyday pictures, so why not turn it on the night sky? Today’s compacts can take reasonable images in low-light conditions, and some even include manual modes that let you take full control of the camera’s functions. The ability to adjust a camera’s settings for yourself will make for much improved images.

With the latest Canon PowerShot compact, you can keep the camera’s shutter open to the starlight for up to 15 seconds, and make its imaging chip very sensitive to light, with ISO values up to 3200. The Nikon Coolpix P500 also allows for manual shooting at these high and sensitive ISO values.

Settings like ISO allow you to capture a wide array of subjects, but there is a downside to compact cameras. Their lens sizes and zoom abilities often don’t let as much light reach the imaging chip as wider DSLR camera lenses do. And being fixed, they don’t have the flexibility of a DSLR’s interchangeable lenses.

DSLR (Digital Single Lens Reflex) cameras offer a much wider range of functions and most experienced astrophotographers will have one in their arsenal. They have the widest range of settings, providing full manual control.

They also have interchangeable lenses so you can swap to a more powerful lens to get close in on a bright star cluster like the Pleiades in Taurus, or a nebula like the Flame Nebula in Orion.

Many DSLRs also have an option to set the opening of the camera’s shutter – the exposure – in increments of seconds up to 30 seconds. After that, they’ll have a bulb or ‘B’ setting for even longer exposures – great for capturing star trails.

In our reviews, Canon and Nikon DSLRs have stood out for what they offer budding astrophotographers. The Canon 300D, 400D and 500D models are all good entry-level DSLRs for astrophotography, as is the Nikon D50 and D90. Fuji’s S3 Pro has also performed well in our tests.

to be continued...

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TECHNIQUE

DSLR camera settings for astrophotography


Bulb


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The bulb setting allows you to precisely control the length of exposures. With it you can take shots lasting from one second up to several minutes and even longer, using a remote shutter release or the delayed timer. Such a wide range of exposures can be creatively exploited in your shots of the night sky. Stars can be made to look like pinpricks with a short exposure or trails with a longer one.

File format


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Many cameras come with a range of file format settings that include RAW, JPEG, RAW+JPEG and even the JPEG settings can have a wide choice of compression levels. Get to know your camera’s file formats and ideally use the RAW setting. While this will produce the highest quality results, it will also save the least number of images on your memory card because of the large file size.

Noise reduction


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This is an in-built facility in many digital cameras and it should be used carefully. When taking pictures with a lot of light across the image, for instance in twilight scenes, noise reduction can improve the shot by cutting out artefacts that are inherent in the camera’s sensor. However, when used on pictures of stars and constellations, noise reduction can remove fainter stars. In these circumstances, it’s best turned off.

Picture styles


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This is another in-built facility that has to be used with caution. Many DSLRs allow you to alter settings like a picture’s contrast, sharpness and colour saturation and save the alterations as a user-defined setting. Subtle adjustments made here can enhance the final image, but it’s very easy to alter a picture too much by going over the top. The default settings are often the best to begin with.

to be continued ...

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MASTERCLASS

Capturing star trails reveals the dynamic night sky


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In the northern hemisphere the stars appear to rotate anticlockwise around one particular star – Polaris, the Pole Star. This star is almost exactly on the celestial pole. It’s not quite, but is certainly close enough for all intents and purposes.

Over the course of 24 hours the stars complete a full circle around Polaris. If you take a 10-minute, wide-field exposure that includes the Pole Star, you’ll see in the result that the stars further from Polaris have longer trails.

The arcs get longer as you move from the pole towards the celestial equator until, at the celestial equator, they are at their longest. South of this the arcs begin to decrease in length again towards the south celestial pole, which for us here in the northern hemisphere lies below the horizon.

Star trail pictures in four steps


Equipment


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Select your lens and fix your camera to a tripod. Adjust the tripod legs so that they provide a solid base. Attach the remote shutter release so you don’t vibrate the camera when taking the shot.

Camera settings


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Select the ISO, switch the camera to ‘bulb’ mode so there’s no limit to the length of the exposure, and focus. Make sure your flash is disabled and switch on the long exposure noise reduction.

Subject


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Decide whether to shoot short star trails near Polaris, or longer trails by aiming at a constellation near the celestial equator. Ursa Minor is good for the former while Orion is good for the latter.

Capture and review


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Take several exposures ranging from five minutes up to half an hour and review them on the preview screen. If the sky is too bright, reduce the ISO and set the aperture to a larger f-number.

to be continued...

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SOFTWARE

Take your shots from camera to the finished product

One of the best thing about digital images is that you can make them even better before you proudly show them off, by tweaking them with photo-editing software like Photoshop or with freeware like GIMP.

With photo-editing software there’s so much that can be done that it can seem a little daunting at first, so we’ve singled out a few key adjustments to make, like adjusting the ‘levels’, the range of light and dark pixels in the image, to change the tone of the image and reduce the effects of light pollution. Watch our software walkthrough below to see what effect this can make.

Key image-editing adjustments


Histogram

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The histogram tool allows you to adjust the contrast and brightness range of the pixels in your image.It’s a very useful aid in making stars stand out and reduces the effects of light pollution. By adjusting the histogram you can bring out detail that may be lost in the background.


Levels

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Like the histogram tool, the levels tool can help reduce the effects of light pollution by giving you control over the amount of red, green and blue in an image. Making subtle changes to the red, green and blue levels can dramatically reduce the orange hue created by light pollution.


Colour balance

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This tool has three sliders, each controlling two colours: yellow and blue, magenta and green, and cyan and red. By moving the sliders you can change the balance of colour between the two colours. Watch the changes to decide how far to go with each slider for the best effect.


Sharpening and softening

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One way to improve an image is to slightly soften or blur the pixels with the softening filter. This reduces the effect of any noise in the image. Use carefully, as it can soften the stars as well. The sharpening filter can also be used to make the image and stars look crisper.

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How to image the Moon
From: Sky at night




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You too can take lunar images like this. Here's where we show you how


Capture our nearest celestial neighbour in all its glory with the second part of our astro imaging masterclass

With its ever-changing face and myriad of interesting features, the Moon is a truly wonderful target for astrophotographers of all abilities. But for all its obviousness and brightness, it takes considerable attention to detail to capture top-quality images of our natural satellite. Here, we show you how to do it.

EQUIPMENT

The kit that you’ll need to begin snapping the Moon

Anyone with a telescope and a basic camera can take a good image of the Moon. But it’s best to use a webcam or CCD camera to take lunar images. These cameras are capable of taking short videos, consisting of many frames per second, which is why specialised lunar and planetary CCD cameras are often referred to as ‘high frame-rate’ cameras.

You can use any kind of scope with these cameras; however, large-aperture Schmidt-Cassegrain and Maksutov-Cassegrain telescopes are popular choices with top lunar astrophotographers. This is because their longer focal lengths are well suited to ‘close-up’ imaging of the Moon, and compared to a high-quality refractor, you get a much larger aperture for your money.

to be continued ...

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Accessories for lunar imaging


Nosepiece

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To attach a webcam to the eyepiece holder on your scope you’ll need a ‘nosepiece’ adaptor. They can be bought from all good astronomy shops for between £12 and £25. You’ll probably need to remove the webcam’s lens first though, before screwing the nosepiece in place.

Filter

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If you are using a monochromatic planetary camera you might find it useful to use a red filter when capturing lunar images. Using one can help produce a crisper final image. A red filter typically costs between £20 and £70.

Barlow lens

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For detailed webcam close-ups of the lunar surface and its craters, a Barlow lens is a must. It increases the focal length and the magnification of your telescope system by typically two or three times. A Barlow will cost you between £40 and £120.

to be continued...

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TECHNIQUE
Dramatic lunar features to capture


Crater Clavius


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This grand lunar crater is a great target if you’re trying to push your equipment to its limit. See how many of the small craterlets you can capture on the crater floor.


Crater Copernicus


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One of the most stunning craters on the Moon, Copernicus makes for a wonderful imaging target. See if you can capture its magnificent terraced walls.


Montes Apenninus


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This impressive chain of peaks is one of the great lunar mountain ranges and a good target for afocal photography. It stretches 600km across the Moon’s surface.


Rupes Recta


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Also known as the ‘Straight Wall’, Rupes Recta is an enormous fault on the lunar surface. The trick is to catch it under the right illumination to see it clearly.


Vallis Alpes


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This dramatic valley cuts straight through the lunar Alps. The challenge with this object is to see if you can capture the elusive rille that runs right the way through it.


Tycho


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Crater Tycho is famously surrounded by bright ejecta rays – brighter material that was flung out by the asteroid impact that formed the crater itself. It has a huge central peak.

to be continued ...

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MASTERCLASS

Make a lunar mosaic to show the Moon at its most majestic

Most high-resolution images of the Moon’s surface aren’t in fact made from a single image, but a mosaic of several smaller panes. Whether it’s a really detailed close-up of a crater or an enormous mosaic covering the entire lunar disc, chances are it was made by carefully stitching together many smaller overlapping images. Learning how to capture and process a mosaic is a crucial part of lunar astrophotography.

The majority, if not all, of the best lunar images are taken with either a webcam or a dedicated lunar and planetary CCD camera. You’ll need a laptop with capture software installed for this type of astro imaging, as well as a telescope with a mount that’s capable of accurately tracking the Moon.

The first step is to take the individual AVI videos. Remember to create a slight overlap between adjacent areas, which will help later with the processing. If you’re making a mosaic of the whole disc, check you’ve covered the entire Moon. You don’t want any gaps!

Next, process the videos you’ve captured to produce the individual panes for the mosaic. You’ll need to stack them in a program like Registax. Once you have the individual panes you can then stitch them together to create a mosaic.

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How to image the planets
From: Sky at night[/URL][URL="http://www.skyatnightmagazine.com/sites/default/files/Best_Saturn_2007_bright%281%29.jpg"]http://www.skyatnightmagazine.com/sites/default/files/Best_Saturn_2007_bright%281%29.jpg (http://www.skyatnightmagazine.com/sites/default/files/Best_Saturn_2007_bright%281%29.jpg)


We show you how to capture stunning images of the planets.

In part three of Astrophotography, The Complete Guide, we show you how to photograph the planets. It's an incredibly rewarding pastime, which can, even today, lead to discovery. Often the announcement of an impact on Jupiter or a storm of Saturn comes from an amateur and is inveriably recorded by a planetary imager.

to be continued ...

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MASTERCLASS

Photograph Mars with a colour planetary camera

Mars comes into opposition every 2.1 years. This is when the planet is best for imaging since its orbit puts it opposite the Sun from our point of view, making it appear at its largest and brightest. Things next start to get interesting from the end of 2011. There’s an opposition on 3 March 2012, when the planet will present a 13-arcsecond disc and reach an altitude of close to 50º from the UK.

Through a telescope there’s plenty to observe on and above the Martian surface. The reddy-brown deserts of Mars are interrupted by dark albedo (shaded) markings that rotate with the planet.

Mars also has seasons and the effects of these can be seen in the growing and shrinking of the planet’s polar ice caps. There’s weather too, and the appearance of bright cloudsor dust storms all add to the excitement of imaging this fascinating world. High surface features such as giantvolcanoes affect the Martian atmosphere. Here you may find bright ‘orographic’ clouds forming as the atmosphere is forced above the volcanoes.

It takes slightly more than an Earth day for Mars to rotate – 24.6 hours – which means that the planet looks very similar from one night to the next, changing more noticeably over the course of several weeks. Detail is subtle and finely structured, so a high-contrast telescope with a large aperture and a long focal length is best for imaging. Large reflectors or catadioptric scopes such as Schmidt-Cassegrain Telescopes (SCTs) are a popular choice for imaging Mars.

Although a monochrome camera with filters will produce the best images of Mars,a colour camera has the advantage that a one-shot full colour capability helps keep the capture time to a minimum – useful since the planet rotates relatively quickly. There’s also less equipment to set up and you won’t need to spend as long processing colour into the image after you’ve captured it.

to be continued...

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The planet holds up well, even under average seeing conditions, so don’t be afraid to pile on the magnification power by using an optical amplifier like a Barlow lens. Aim to keep your scope’s focal ratio in the region of f/25 to f/45. Following the methods in the ‘Technique’ section, you should end up with an image of the planet in the capture software that shows as a bright and tangible disc. If your camera has a gamma control option, keep this at the default level, adjusting exposure and gain to get the level right.

An IR-blocking filter is essential for good results and some colour cameras have this built in by default. If yours doesn’t, you can get a separate filter for around £30 that normally screws into the front of the eyepiece adaptor.

It can be tricky to get the right colour balance with Mars. Before manually adjusting your camera’s colour settings, if you’ve managed to get a large and bright planetary disc in the frame, try using the camera’s auto colour-balance function. If necessary, push the gain up high to get a bright enough signal. This should also alleviate the so-called ‘onion-ring’ effect, which can occur after registration and stacking has been applied. Under certain seeing conditions you may get a ‘false edge’ effect on processed results; however, you’re at the mercy of the sky.

The capture file will need to be processed with registration and stacking software like RegiStax or AviStack. These pick out the best frames, align them and then stack them together automatically to reduce frame noise.

In order for this to work well, you do need a good number of frames to start with. High-frame-rate cameras can easily generate several thousand frames during a capture run. A webcam operating at a more sedate 10fps over a typical three-minute run will net 1,800 frames which, although towards the low end, should be enough to produce an acceptable result.

When passing the capture file through stacking software, expect the number of frames that make up the final stacked image to be just 10-20 per cent of the full frame count. If the final result shows colour fringing, it can be corrected by re-aligning the colour channels either in a graphics editing program or using the RGB colour-align function that some programs have.

to be continued ...

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Sharpen your images of Mars with Registax

1. Reference Frame

RegiStax analyses your capture file to assess how sharp and well defined each frame is. Load your capture file (typically an AVI movie file) using the ‘Select’ option and then adjust the lower slider so that a particularly sharp frame is displayed. This will be the reference against which the others are compared.

2. Placing the Alignment Box

An alignment box should be placed over a region of high contrast in the reference frame. Typically this will be the main planet’s disc, so choose an appropriate ‘Align box’ size to do this, but don’t worry if some of the disc falls outside the box. Move the cursor over the image and left click to place the box.

3. Align

Check the ‘Use pre-blurring’ option and then click on the ‘Align’ button. RegiStax runs through each frame, comparing it to the reference frame. The end result is a graph (‘RegiStrationgraph’ as it’s called). A red line shows the image quality and a green one shows the movement shift between frames.

4. Limit

There’s a quality bar in the graph, which can be moved using the slider at the bottom of the main window. Dragging the bar right adds more frames to the final stack and improves noise but also brings more poor quality images into the process. Drag it to the point where the red line indicates 80-90 per cent quality.

5. Limit and Process

With your decision on the placement of the quality bar made, click ‘Limit’. This tells RegiStax to ignore any frames to the right of the bar. Follow this with a click on ‘Optimize & Stack’, which will instruct RegiStax to align all of the images to each other and then combine them in a stack to reduce noise.

6. Wavelets

The Wavelet’s control sliders allow you to sharpen different levels of detail in the processed image. Click on each slider’s ‘Preview’ button to reveal the type of detail that will be affected by adjusting the slider. Choose the level that you find works on detail rather than noise and move the slider to the right.

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Imaging the Sun

From: Sky at night




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Taking an image of the Sun can reveal fine detail on the surface of our local star



Taking an image of the Sun is a fascinating astronomical pursuit that gives you the opportunity to study a star close-up. There are other advantages to solar imaging: it can only be done during the day when the temperature is normally quite pleasant and, with plenty of light around, you can say goodbye to fumbling around with red-light torches. Of course, there’s a real danger from the intensity of light – it’s one of the only times that astronomy can pose a risk of physical injury. In this course, we’ll look at how to image the Sun safely.

to be continued...

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MASTERCLASS

Imaging the Sun with a white-light filter

Imaging the Sun in its natural ‘white’ light is an inexpensive way to get into solar photography. When you pay attention to the safety issues, it can be a very rewarding way to monitor our nearest star.

One of the most basic methods is to use solar projection. For this you’ll need a small refractor, ideally mounted on a driven equatorial mount. With your scope pointing away from the Sun, fit a non-plastic, low-power eyepiece and ensure the finder is removed or capped.

Watching the scope’s shadow on the ground, turn it to point directly at the Sun. A piece of stiff white card held behind the eyepiece will catch the Sun’s image, while a tweak on the focuser will bring it into sharp relief.

A card shield taped to the objective end of the tube may help improve contrast if the projection is difficult to see.

Now set your camera to automatic and take a shot of the image on the card screen. If the image comes out too bright, try moving the screen away from the eyepiece or, if you have manual controls, try under-exposing the shot.

This basic method is capable of showing the photosphere, limb-darkening, sunspots and faculae – it is, however, only suitable for refractors.

A more sophisticated method, also limited for use with refractors, is to use a device called a Herschel Wedge inserted in the eyepiece holder.

The wedge basically blocks most of the harmful heat and light from the Sun, reducing its intensity to safe viewing levels.

A more universal method that is suitable on any type of telescope is to use a white-light filter such as Baader AstroSolar Film or Thousand Oaks Solar Filter.

AstroSolar Film is available in A4 sheets. It costs around £15-£20 and comes in one of two types: one with a neutral density of 5.0 for visual work or a slightly brighter neutral density of 3.8 for imaging.

Larger 100x50cm sheets are also available. See the step-by-step below for instructions on fitting a solar filter for imaging.

With a filter fitted you can image the Sun just as you would the Moon. In fact, the same constraints apply because the Sun’s light is just as susceptible to our turbulent atmosphere.

Stills cameras such as DSLRs are good for low-power shots, but webcams or preferably high frame-rate planetary cameras are more suited for close-ups.

For optimal results, however, screwing a solar continuum or green imaging filter onto your camera’s eyepiece may enhance contrast in sunspot detail and solar granulation.

to be continued...

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STEP BY STEP

How to set up and capture solar images

1. Fitting the filter

With the scope pointing away from the Sun, remove its lens cap and fit the solar filter; remove or cap the finderscope too. Make sure everything is securely fastened. If required, use a bit of low-tack electrical tape to hold the main filter in place securely. This is especially important on a windy day.

2. Line up with the Sun

Lining the telescope up with the Sun without the use of a finderscope isn’t as hard as it sounds. Without looking along the tube towards the Sun, roughly align the scope and then look at its shadow. As the scope approaches the correct alignment, so the tube shadow will reach minimum size.

3. Keep it in the dark

If you find it hard to see detail on your laptop’s screen in sunlight, you’ll need a dark enclosure. A simple one can be made by putting a blanket over your head and the computer, but for something more sturdy, try placing the laptop in a closed cardboard box with a slit cut in it to see the screen.

4. Insert your camera

If you have one, screw a solar continuum or green imaging filter onto your camera’s nosepiece. Insert the camera into the eyepiece holder of your scope and fine-tune the scope’s position so that an image can be seen on your computer’s screen. Locate the Sun’s edge and focus roughly.

5. Settings and focus

Using the highest frame-rate, reduce gain and then exposure until the image is correctly exposed and contains no white. If you can’t, you may need to use a neutral density filter. Rotate the camera so that any spots visibly move horizontally across the frame while slewing in RA. Finally, fine-focus the image.

6. Capture

For low image scale (magnification) setups showing all, or at least a large portion, of the Sun’s photosphere, aim to capture 500-800 frames. Increase this up to around 2,000 frames for larger image scales. If your camera offers it, reduce its gamma slightly to make granulation and spot detail easier to pick out.

to be continued...

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TECH TALK

Finding your focus

Focusing is a critical skill to master in any form of astronomical imaging; without it, you’ll get poor results.

If you’re just starting out, accurate focusing can be quite hard to get to grips with, which can make the whole imaging experience rather frustrating. There’s no real reason why this needs to be the case, so here are a few tips on how to get your images as sharp as possible.

First, make sure your camera is securely locked into your telescope’s eyepiece holder and that the focuser tension adjustment is set firm.

You want to be able to move the camera back and forth quite easily, but you also want it to stay where you’ve put it. Locate a high-contrast part of the Sun.

For white-light imaging, the best target is the Sun’s edge. For more exotic filters, the Sun’s surface is normally sufficiently detailed for you to lock onto that.

Even here, though, it’s good practice to choose a sunspot group or perhaps a dark hydrogen-alpha filament to give you a better focus target.

With a gentle grip on the focuser, move in towards focus; getting slower as you appear to be reaching the critical point.

When you do reach this point, keep going, coming out of focus again on the other side. Then, reverse direction again, passing slowly through focus, this time from the other side.

Do this a few times until you’re confident that you can recognise the real focus position; then adjust the focuser until you’re in that position.

[رخساره روشنی]

SOME THING ABOUT YOUR CAMERA First lets go over some quick facts and terms about digital cameras.


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Shutter Speeds, Aperture, ISO

Except for the moon, the stuff we want to shoot in the night sky is pretty faint. That means we need to record as much light as we can. Cameras control the amount of light taken in a picture by two basic ways. There is a shutter that opens and lets light hit the digital sensor in the camera, and there is a variable-sized hole, called the aperture or diaphragm, in the camera lens. If we leave the shutter open longer, we record more light. If we use a larger hole, we let more light in. Nothing complicated here.

Shutter speeds run in fractions of a second, usually around 1/1,000th of a second at the shortest exposure to many seconds at the longest. Most DSLRs also have a setting called "bulb" that keeps the shutter open as long as you press the shutter button down.

Aperture settings run in a crazy series of numbers like f/2.8, f/4, f/5.6, and f/8. Confusingly, the smaller the number, the larger the hole in the diaphragm. So, f/4 is a bigger hole than f/8.

..... to be continued

[رخساره روشنی]

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Most cameras also have a way to change their "sensitivity". This is kind of a trick setting though. You can't really change the sensitivity of the sensor in the camera, but you can adjust a setting called the ISO, which is sort of like a multiplier factor. ISOs may run from 100 to 400 in simple cameras, or up to 800, 1600 or 3200 in more expensive cameras. The higher the ISO number, the brighter the resulting image will be. Unfortunately, the noise, or grain, gets worse at the higher ISOs, but we won't worry about that for now.

To get started, you will have to figure out how to get your camera to use as long a shutter speed as possible, at as wide an aperture as possible, and at as high an ISO as possible. Unfortunately, you may have to read the manual to learn how to do this. Sorry. Your other option is to just dig around in the camera's menus looking for these settings, but sometimes they can be hard to find and not labeled very clearly.

Set the camera on manual exposure if it has that setting. Then set the lens to its widest opening, usually f/2.8. Set the ISO to the highest it will go, usually 400 for simple point and shoot cameras. If the camera doesn't have a manual exposure setting, set it to night mode.

..... to be continued

[رخساره روشنی]

Focus

The next thing you will have to worry about is the focus. Once again, dig through the camera manual, or menus, and see if you can figure out how to turn off the autofocus, and manually focus the camera on infinity (the farthest away that the camera will focus).


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For more sophisticated digital cameras like DSLRs, you can pre-focus the camera in the daytime on something very far away, and then turn the auto-focus off. If you have a DSLR with a lens that you can manually focus, focus it on infinity and tape it down. Beware, many of these lenses actually will go past infinity, so you can't just trust the markings on the lens.

Experiment with this in the daytime. If you have a point and shoot camera, it may have a setting for shooting at infinity and may have some type of icon of mountains to indicate this. Try shooting something very far away to be sure the setting works.


White Balance

Light-polluted red sky with auto white balance.

Many cameras also allow the white balance to be selected by the user. Once again, this setting will be buried in a menu somewhere.


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Most will be set to auto white balance by default. This usually doesn't give great results for nighttime photography, especially if you are shooting anywhere that has light pollution. This will usually make the sky a brown/red color. Try setting the white balance to Tungsten for long exposures of the night sky. This can give a more pleasing sky background.

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Introducing deep-sky photography

from: sky at night


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Imaging deep-sky objects, like the globular cluster M13, captures the beauty of distant space



Deep-sky astrophotography produces some of the most spectacular images in astronomy. It’s immensely rewarding, but is also perhaps the most demanding of all the subjects covered in this series. Capturing and processing your images presents a whole new set of challenges for both you and your equipment as the requirements are very different from the subjects we’ve covered in the previous four parts of this guide. Here we’ll show you the best way to set up your gear, capture the data and process it to create your own deep-sky images.

to be continued ...

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MASTERCLASS

Capture the globular cluster M13

Here we’ll show you how to capture an image of the popular globular cluster, M13, in the constellation of Hercules. You can use a one-shot colour CCD or a DSLR camera for this object.

Focus your camera on mag. +2.8 Zeta (ζ) Herculis, the star at the bottom right of the Keystone asterism in the centre of Hercules.

Remember to remove your Bahtinov mask if you used one and slew up towards mag. +3.5 star Eta (η) Herculis at the top right-hand corner of the Keystone asterism. M13 is to be found two-thirds of the way between the two stars.

The cluster’s apparent diameter is 20 arcseconds, so a focal length of 650-1,200mm would be ideal – well within reach of many popular reflectors and refractors.

A smaller focal length may not work as well, as globular clusters lose their visual impact if the field of view is too wide.

Framing isn’t too critical for this circular object but you might wish to include the two contrasting colour stars in your image – blue to the south and reddish to the east – or even the magnitude +11.6 galaxy, NGC 6207 to the northeast.

M13 is fairly bright at mag. +5.9 but it has a bright core soyou’ll need to be careful not to overexpose it and burn out the centre.

Exposures in the region of 60 seconds at an ISO of between 800 and 1600 for a DSLR camera, or 120-150 seconds with a one-shot colour CCD camera, should capture some good detail.

Take at least 10 images but preferably more – up to about 30 – at these settings, using RAW mode on your DSLR camera or unbinned if you are using a CCD camera.

You can automate the process with the software that controls your CCD camera but if you are using your DSLR camera without a laptop, a programmable remote shutter release (readily available from camera stores) will do this for you.

If you are manually operating your DSLR camera be sure to use a remote shutter release, as a minimum, to avoid camera shake. Complete the session by taking 16-20 dark frames, bias frames and if possible, flat frames.

Using suitable software such as MaximDL or Deep Sky Stacker, you should now calibrate and stack your images.

Deep Sky Stacker will import your light, dark, bias and flat frames and automatically carry out the various processing tasks for you to give a calibrated, de-Bayered (to generate the colour channels captured by the Bayer filter) and stacked image ready for importing into a photo-editing program like Photoshop or GIMP.

MaximDL, on the other hand, will break the process down into modules. The first operation stacks the calibration frames into master frames. These masters will then be applied to each of your light frames. Save the result in a new folder if you wish.

Stack the calibrated light frames to produce a final FITS-format file, then save a copy in TIFF format for final processing in Photoshop or GIMP.

to be continued ...

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STEP BY STEP

Imaging the globular cluster M13

1Polar alignment

To ensure that your mount tracks the sky as accurately as possible and to help your Go-To system to locate objects first time, make sure that you carry out an accurate polar alignment. Using a polarscope is quick and easy, so don’t compromise as it will be a little time well spent.

2Getting balanced

Your mount will work most efficiently if you limit the amount of load it has to move. Getting an accurate balance will go a long way to achieving this. Balance the dec axis first with all of your equipment installed and the camera at approximate focus, then balance the RA axis.

3Slew to Zeta Herculis and focus

Align on a bright star near Hercules, attach your Bahtinov mask and adjust focus until the cross is bisected by the line. Remove the mask and slew to Zeta Herculis, centering it on your camera’s sensor. If your mount has the facility, synchronise on this star and slew to M13.

4 Capture your light and calibration frames

Start your imaging run, aiming for as many images as possible. Unless you already have a library of bias and dark frames (at the correct exposure length), leave time for these. Flat frames must be taken on the night or the next day without touching the camera or focus.

5Calibrate, de-Bayer and stack

Using your stacking software, apply your calibration frames to your image data to remove unwanted artefacts. Unless your software does this automatically, de-Bayer your calibrated frames and stack them using the ‘SD Mask’ or ‘Kappa Sigma’ option.

6Post-processing

You should already be seeing a reasonable image now but this is just the starting point. Export your image as a TIFF file (preferably 16-bit) and load it into either GIMP (8-bit images only) or
Photoshop (16-bit). Start by applying a gentle ‘Levels’ adjustment to release detail in your image

to be continued...

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NEED TO KNOW

Camera control software

DSLR

If your camera software allows you to take exposures of a minute or more, use it to set the ISO value to 1600, white balance to auto, file format to RAW, noise reduction (if available) to off and shutter speed to 60 seconds.

If not, set these values manually, then set the shutter speed to ‘bulb’and use a manual or programmable remote shutter-release cable to trip the shutter for a 60-second exposure.

There’s no aperture setting because telescopes don’t have a variable iris. If your software doesn’t allow a ‘live view’ image on your laptop, take a series of 10-second exposures using a Bahtinov mask and adjust the focus in between shots.

CCD camera

CCD cameras need software to control them. Programs such as MaximDL and Nebulosity will do this.

Some CCD cameras have a gain control but use with caution to avoid increasing noise levels from the camera’s sensor.

Set exposure length to between 100 and 120 seconds for the imaging run but for focusing on a bright star, 6-second exposures with 2x2 binning will suffice.

Unlike a DSLR camera, there’s no image processing built in, so images are automatically taken in a RAW state. If you have set-point cooling, set it to -25º and set the binning mode to 1x1.

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Advanced deep-sky photography

from: Sky at night
[/URL]http://www.skyatnightmagazine.com/sites/default/files/AP6_main_pic%281%29.png (http://www.skyatnightmagazine.com/sites/default/files/AP6_main_pic%281%29.png)

Capturing an image of The Wall in LRGB produces striking colours and sharp contrasts



In part six of our guide to astrophotography, we’ll be taking deep-sky imaging to the next level

In part five, we looked at producing deep-sky images with DSLR cameras and one-shot colour CCD cameras

This time we’ll be concentrating on deep-sky imaging with mono cameras and external filters

These don’t rely on built-in colour filters to encode the colour data, as well as having increased sensitivity,[U] enabling you to produce sharp, exquisitely detailed deep-sky images

to be continued...

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MASTERCLASS

Imaging The Wall, the brightest part of NGC 7000, using LRGB filters

Here we’re going to show you how to produce a full colour image using LRGB filters and a mono CCD camera.

A mono CCD camera is a very versatile piece of equipment; it lets you capture data using a wide range of filters to achieve different results.

Add to this the ability to take long exposures with reduced electronic noise, thanks to these cameras’ in-built Peltier cooling, and it becomes a very powerful tool.

Your choice of filter size will be dictated by the size of your sensor as well as your pocket. Although it is possible to remove the camera and replace each filter in turn, this is really not recommended!

It becomes a tortuous task to make sure that everything goes back in place correctly to ensure that the individual groups of images line up with one another, so a filter wheel is a real must-have.

Although a software-controlled electronic wheel is very nice, a manual wheel removes a level of complexity from the system and is pretty much guaranteed to have repeatability of filter placement each time.

Despite ranges of good-quality filters being designed to be parfocal, wise astrophotographers will always check focus when swapping to the next filter so unless you have completely automated focus as well, the appeal of an electronic filter wheel diminishes further.

to be continued ...

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However, electronic wheels do have one great advantage over their manual siblings: once the filters are loaded in they are light- and dust-tight because there is no wheel edge projecting out of the casing for you to manually revolve.

It is useful to plan an imaging run carefully in advance to make sure that you make the best of your available time.

In LRGB imaging, your luminance data is the most important as this decides the deepness and detail features of your image, but how you capture your RGB data can have a great effect on the final image too.

What you’re trying to achieve in RGB imaging is a finished picture that replicates the colours seen by the human eye through matching the spectral sensitivity of the CCD’s sensor to your eye.

The human eye is most sensitive to green light whereas a CCD sensor normally has its highest sensitivity in red light, which is great for imaging emission nebulae.

However, the use of filters and a naturally occurring effect known as ‘atmospheric extinction’ that reduces the brightness of night-sky objects, will further skew the sensitivity of the sensor to red, green and blue.

If you were to take equal length exposures for each of your three colour filters your images could end up with a colour cast to them (which is why DSLR cameras have an automatic ‘white balance’ feature built in).

To compensate for this skewed sensitivity, it is necessary to either take different length exposures for each colour or to adjust an image’s colour balance later in postprocessing.

The atmosphere naturally scatters blue light more than the other colours so if you can reduce the amount of atmosphere that the blue light has to travel through, your blue data will be crisper and less noisy.

Aim to capture your blue data when your chosen object is at its highest in the sky.

Just as important as your image data are your calibration frames. Bias frames are not dependent on the filter in use but your flat frames most certainly are, especially if you are hoping that these frames will remove any ‘dust bunnies’ in your images.

Although dark frames are not directly dependent on the filter in use, bear in mind that if you have used different exposure lengths for each filter, you will need dark frames of a matching exposure length for each filter too.

to be continued ...

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STEP BY STEP
Create a spectcular image of The Wall using LRGB captures

1Luminance

With the luminance (IR) filter selected, good focus achieved and the autoguider running, start your imaging run. It always pays to capture luminance first so that if the clouds roll in during the session, at least you’ll have something worthwhile for your trouble. Take at least 10, 480s exposures.

2Red channel

With the luminance data under your belt you’ll have a pretty good idea of what your image is going to look like even though it will only be in mono, so change the filter to red and carefully re-check the focus, adjusting it if necessary. Take six 240s exposures, binned 2x2.

3Blue channel

Assuming that about now, NGC 7000 is high in the sky, change filter to blue and re-check the focus. If you are using an ED doublet refractor there is a good chance the focus will match that of the red filter and with a triplet refractor, it should be bang on. Take six 360s exposures, binned 2x2.

4Green channel

The final part of the capture is through the green filter. If the cloud rolls in before you capture this set, there is a way of producing a full colour image from what you’ve already captured. Check focus again because if any colour will be out, it’ll be this one. Take six, 300s exposures, binned 2x2.

5Calibration

If you have an electro-luminescent panel or light box, capture your flat frames immediately after you’ve taken each set of filtered images, or take them the following day without disturbing the focus. The bias and dark frames can be taken inside at any time. Calibrate each set of filtered images.

6Stack, align and combine

Stack the images into four masters, double the size of the red, green and blue masters and align each with the luminance in Photoshop. Produce an RGB file the same size as the luminance and populate each channel with the matching colour. Paste the luminance channel on top and set the blend mode to Luminance.

to be continued ...