Last updated on
4/11/2006

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Rather than using film, you may use a digital camera to capture the images in your scope.  Digital cameras for astrophotography are called CCD cameras, because the solid-state device that captures the image is a Charge-Coupled Device (CCD). CCD cameras have become very popular for astrophotography. (It is also possible to use a consumer digicam for astronomical objects - go to the Consumer Digicam page for more information about this topic.)

CCD cameras for astrophotography are not the cameras sold for normal (terrestrial) photography - they are specialized cameras designed for long exposures with telescopes. They eliminate the dark current problems of CCD chips by cooling the CCD chip - click here for an explanation about how they do this.  They mount on the rear cell of a scope - replacing the eyepiece - and connect to a computer (laptop or desktop) so you can capture and store the image. They are optically much, much faster than film, typically requiring exposures on the order of seconds or at most minutes for deep-sky objects, and they are able to capture a far greater range of brightness than film. In fact, in any given scope they can show you images you can�t see well with your eye through the scope. For these reasons they have replaced film for use at professional observatories, and it is CCD cameras that are used in the Hubble Space Telescope (albeit a CCD camera with capabilities and a price most of us cannot afford.).

CCD cameras usually come with software that allows you to merge a number of exposures into one image.  This means that each individual exposure can be short, so you don�t need to manually guide the scope for long periods of time, a major advantage (and astrophotographers are finding that this allows you to shoot Deep-Sky Objects with Alt-Az-mounted scopes, obviating the need to mount a heavy fork-mounted scope onto an equatorial wedge). Another advantage is that you can bring the resulting image into a photo-editing application (Adobe Photoshop is typically used) and extract more information from the image or clean it up digitally. 

There are two issues with CCD astrocameras.  One is that if you want to create a hardcopy print of your image you need a very good photo printer.  Some astrophotographers cite this as a reason to use film - the quality of the print from film on photographic paper has a higher resolution than a print from a digital image on a photo printer. Ironically, some astrophotographers who use film are finding that their images can be improved by scanning them into a computer with a film scanner, and editing the images. At that point they would still be required to print the image digitally, not with normal photographic print paper. So it seems to me that the direction of the future is clear.

The second issue with CCD astrocameras is that the size of the CCD chip (at least, ones that sell for less than $10K) is a lot smaller than the size of 35mm film. Most deep-sky objects will be much larger than the size of the CCD chip, in your scope�s normal configuration. If you want to do deep-sky (rather than planetary) imaging you will need to convert the scope into a wider-angle optical instrument.  One common way this is done for SCTs is with a Focal Reducer attachment to the rear cell.  But the real advantage unique to many of the Celestron SCTs is the Fastar system, which creates an f/2 instrument (or thereabouts, depending on the particular model) that gives you the ability to capture large deep-sky objects. With the right CCD camera you can use the Fastar system for deep-sky photography or mount the CCD camera on the scope�s rear cell for planetary photography - the best of both worlds! Click on the Fastar & Pixcel button at the top of this page for more details on the Fastar system.

The choice of a CCD camera for astrophotography can be a rather complex subject, primarily because CCD chips for astrophotography haven�t reached the low consumer prices that digicams have - they have a much more limited production and are thus expensive, so the cameras require a trade-off between price and capabilities.  Go to the Choosing a CCD Camera page for more information on this.

For an overview of CCD imaging see the Introduction to CCD Imaging by Arthur Babcock and Robin Casady. If you seriously plan to delve into CCD photography, get Richard Berry�s book.  If you want to get a better idea of the field of view of different CCD cameras, click here for a description of Field of View calculators available through the Web. But keep in mind that the whole question of matching a CCD camera to a scope is more complex than just the field of view.
 

Back to Astrophotography Basics
 

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