The utilization of Digital Cameras for Astrophotography has become more and more inexpensive and appealing. Since the typical consumer digital camera can be used for regular picture taking as well as astrophotography, the cost is even more justified.
I have always been interested in Astrophotography but thought it was beyond my resources and capabilities. After purchasing a digital camera about a year ago, I was doing some research on the Internet looking for tips on how to use it better when I ran across information on how to use a digital camera with a telescope! Since then I have been obsessed with Digital Astrophotography.
using firewire. In fact, it may be desirable, with much patience, over the single shot of the Digital Camera in that you can stack tens or hundreds of images into one image to achieve the desired result. This can be done through various software packages some of which I will mention later on. Some good results on lunar, solar, and planetary images can be achieved but DSOs are pretty much out of the question since long exposures are not possible.
Digital Web Cam Astrophotography is similar to Video Cameras capabilities but require the images to be directly downloaded to a connected PC and resolution is usually limited to 640 x480 or lower. This seems to be a popular method since the cost of getting started is very low. Some Web Cams can also be modified to take extended exposures. For example, I purchased a Phillips Vesta Pro 680 camera for $18 and had it modified at a cost of $60. Finally, I purchased an adapter for $20 to attach it to my telescope using primary focus (without eyepiece). So, for under $100 I now have a CCD camera capable of taking long enough exposures to capture DSO objects. Of course, you still need a PC or a Mac.
CCD AstroCams are the devices used by serious Astrophotgraphers designed specifically for astrophotography. One of the primary differences that distinguish these cameras from the other types is that they are cooled to greatly minimize “hot pixels” or “noise” created from heat within the CCD chip. These types of cameras produce outstanding images of DSOs but much more than a typical general consumer-type Digital Camera. I have seen the costs ranging between $2000 and $45,000 for AstroCams. Decent color AstroCams start at about $4500. A PC is also required but a Mac can be used as well.
Consumer Digital Cameras have become very popular. They allow you to take a digital image afocally and store it onto media that can be transferred to a PC or taken to a Photo Processor for processing.
The camera and accessories you need will depend on the type of objects you want to image. I would suggest that first you decide what you want to be able to do. Lunar and Solar shots* are the easiest to take and process while planetary and DSOs become more difficult. The following chart is a collection of my thoughts on what you can expect depending on the targeted object. Note: this is combination of my experiences and results I have had and seen of others and you may find this may vary for you and your equipment.
* Warning – never use a camera or telescope for
What is needed?
Cameras – When selecting or using a camera for Astrophotography certain features are beneficial and can be critical.
Important Features - Manual settings such as shutter and aperture control, exposure times (up to 30 seconds or more depending on aperture for DSOs objects), manual/infinity/macro focus selections, ISO settings of 100, 200, 400, or even 800, Optical Zoom of 3x to 10x (recommend disabling digital zoom), contrast / lighting / sharpness, a timer / remote control, flash disabling, output for external monitor, and threaded for lens accessories.
Resolution – Any Mega pixel camera can give you high enough resolution for viewing images on a computer. Many people reduce the resolution down to even 300x200 for displaying on web pages. If you want to print your images, then you may want a camera that can do 2 Mega Pixel or greater.
Accessories – Power pack or at least rechargeable batteries, serial/ USB/Firewire connection to computer, remote shutter control (prevents shaking the telescope).
Memory – The kind and size of memory will depend on what types of formats your camera stores images and whether it is compressed. The resolution of the image will also factor in. Most do JPG compression. Some will allow uncompressed Tiff or BMP files. For example, if you are using a compressed format at 2 Mega Pixel taking shots of Saturn you should get at least 200 to 300 pictures on a 64MB card. In uncompressed mode you may only be able to get 15 to 30 shots.
Popular Cameras Used – The big three I have seen mostly used are the Nikon Coolpix 850/9xx (I have the 990), Olympus 20xx/30xx, and Casio QV xxxx. There are many others but these seem to have most if not all the necessary features most people want for Astrophotography. The costs for these range from about $300 to $750 (see links below for more info) and are dropping quickly. They can also be obtained used for less expense.
Telescopes – Just about any type of telescope can be used. Important considerations are:
Telescope mount/tripod/forks – The more stable or sturdy of course the better.
Aperture – Size really does make a difference, especially when imaging fainter objects.
Balance – Smaller telescopes might be more susceptible to balance problems with the weight of the camera attached.
Focusers – Focus is obtained by the telescope, not the camera. Many telescopes tend to shake or vibrate when focused making fine focusing very difficult. Electronic focusers can be added to help with this problem if needed.
Tracking Ability –Tracking becomes critical when attempting to image DSOs and smaller planets. It can also help with larger planets, lunar and solar imaging.
Mounting / Connecting – There are many methods to attaching your camera to a telescope. It can be easier and cheaper if your camera is threaded for accessories. You want your camera lens positioned as close to the eyepiece as possible to help prevent / reduce vignetting. Vignetting is an effect that shows up as a darkened area circling your image much like looking through a tunnel or a tube. A couple methods of connection are:
Attach the camera via thread-on adapters. Obtain a threaded step-up ring for your specific camera thread size to a standard 38mm. Then you can either use a 38mm adapter that clamps / couples onto your eyepiece or a threaded T-Adapter that the eyepiece can be inserted into. I prefer the coupling adapters. (See link below for more information on camera adapters). Another method is by using various “Universal Camera Adapters” that use the camera’s tripod threads to attach to a mount that is positioned over your eyepiece. This method may be more universal, but is typically more expensive.
Connect a monitor or TV to your camera to give you a larger view than your camera LCD to focus on. This can also be combined with the Hartman Mask.
Zooming – Zooming in on the focus object can also help. You can even use digital zooming for this, but make sure you turn it off prior taking shots of your target.
Camera Settings –
ISO – A balance must be met here. Higher ISO settings mean you can do shorter exposures, which typically equates to sharper images. However, it can also add more general noise and hot pixels due to the higher sensitivity/gain setting of the CCD chip.
Optical Zoom – Zoom is very desirable for planetary imaging. There is currently a big debate over whether it is better to use more zoom of the camera or more power in the telescope. I have not seen any proof for either way yet, but I am currently leaning towards more camera optical zoom may be better based on my observations and theories. Zoom also helps reduce vignetting.
Digital Zoom – Digital zooming is not recommending for taking images. There is no advantage in using this feature since this is basically resizing/cropping the object and can be done later during image processing if necessary.
Light/White Balance – This varies somewhat between cameras. It can affect the resulting color of the object being imaged. Many recommend Black and White for lunar shots.
Exposure – This varies greatly depending on telescope/camera aperture, viewing conditions, and the object you are imaging.
Resolution – You must experiment to see what works best for your needs. Factors include the target object to image, the amount of available memory, and whether you plan to view these images on the screen or print them in photo quality. It also takes the camera longer to store higher resolution images and it can be more difficult to work with them in some graphics packages. Higher resolution can give you better quality results, though.
Other settings – Flash should be off! Typically, I stay with auto settings on all other settings. Some recommend disabling most settings since you can always adjust things later in software.
Taking a DarkFrame – If your object requires longer exposures than ¼ of a second and your camera does not have an automatic noise reduction feature then you may want to take what is called a Dark Frame shot. This can be used later to subtract out the Hot Pixel and Noise produced by you camera during long exposures. The Dark Frame must be taken for the same duration and camera settings as your imaging session. It is suggested that you take one of these prior to and after a session for each change in exposure time and / or picture setting. You can take these by simply capping off the telescope or by removing the camera from the telescope and covering up the camera lens with the lens cap where no light can get in.
Conditions / Location – Obviously, better seeing conditions are going to yield better results. Planetary, lunar, and solar images are more affected by poor seeing than DSOs and Constellations. On the other hand, Planetary, lunar, and solar images are less affected by light pollution while DSOs and Constellations are. DSOs and Constellations are also affected by bright moon light. The higher in the sky your target image is the better (less atmosphere distortion). Planets should be at least 50 degrees or higher for good results while DSOs are more forgiving
Software – In some cases you may be happy with the raw image straight from the camera. In most cases, at least some tweaking is necessary. Stacking multiple images can also be very effective and can simulate extended exposures. The idea here is that many images of the same size and resolution can be combined to produce an image that has less noise and greater detail in it. You will want to only stack images taken within minutes of each other to help minimize field rotation (for alt/az mounts) and object rotation (Jupiter rotates very fast). Typically, the software that came with your camera will allow you to resize, crop, and adjust contrast and color balance. Other software may be needed to perform stacking, DarkFrame removal, file conversion and other enhancements. There are some nice freebies out there such as IrfranView and DarkFrame. Some of the more popular commercial packages include Paint Shop Pro and Photoshop. Some advanced Astrophotography related software available are AstroStack, AIP4WIN, Cadet, Iris, Gimp, and AstroArt. (See links below for more information about these software packages).
Printing – Inkjet printers can do a nice job at this and some paper and inks are now rated at 10 years or more. You may want to use higher resolution images for better results. Since the background is usually black, you may want to closely crop your image to not waste ink.
Effect Digital Astrophotography has three distinct skills sets that I have identified so far. First is the astronomy aspect of knowing the sky and using a telescope. Secondly, is learning how to use your digital camera well. Finally, comes the computer processing skills of processing and enhancing the images. It can be a big learning curve for some but can be overcome in time with patience, practice, and perseverance. It can be a very fun, challenging, and rewarding experience.
Highly Suggested / Helpful Links Tips and FAQs
Digital Astrophotography Group - http://groups.yahoo.com/group/digital_astro/
Digital Camera Astrophotography FAQ - http://www.erols.com/szykman/Astro/AstroDigiCamFAQ.html
Getting Started Guide to Digital Camera Astrophotography – http://groups.yahoo.com/group/digital_astro/files/GettingStartedGuide.pdf
Imaging Cookbook for Beginners - http://groups.yahoo.com/group/QCUIAG/files/Imaging%20Cookbook%201.0_word6.0.doc by Jay Timmermans
Digital Cameras and Accessories
Comprehensive overview of many commercial adapter solutions - http://www.erols.com/szykman/Astro/Adapters.html
Hartman Mask Link - http://www.incessant.com/gap/astrophotography/Coolpix/diyhm/
CCD Article by Eric Meisenzahl, Eastman Kodak Co. - http://www.sensorsmag.com/articles/0198/cc0198/index.htm
BlackFrame (removes noise) - http://www.mediachance.com/digicam/blackframe.htm
Image Processing Links - http://groups.yahoo.com/group/digital_astro/links/Image_Processing_Sof_000999519803/
Catching the Light Site by Jerry Lodgriguss (good tips) - http://www.astropix.com/HTML/K_MISC/TOC_SITE.HTM
- By Bob Shabowski
Copyright © 2002, Bob Shabowski