Last updated on
4/11/
2006

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Astrophotography Basics

There are a whole lot of beautiful objects in the sky, and you can spend a lifetime visually observing them and showing them to your family and friends. (In fact, the first time you show someone Saturn or Jupiter and they say, “Oh, wow!” I guarantee you will have found your purchase of a scope really worthwhile.)   However, you may find that at some point you want to capture astro objects as photographic images.  You can do that, assuming you purchased a telescope and mount designed to be rigid and vibration-free enough to support astrophotography.  There are four ways you can photograph astral objects : with a 35mm camera and film, with a consumer digital camera (although your options are somewhat limited with these), with a digital camera specifically designed for astrophotography - called a CCD camera, or with a webcam (which is currently used specifically for planetary photography).

Click on the “35mm & Film”, the “Consumer Cams”, the “CCD Camera”, or the Webcams button above, for more information. Click on the “Accessories” button to review a number of accessories that will make astrophotography easier for you.  For specific information on the Celestron Fastar system, available for most Celestron SCT models, click on the “Fastar & ST-237” button. 

Traditionally you have needed to mount your scope on an equatorial wedge to do most types of astrophotography.  This is because the stars rotate around the celestial pole, so if you track them with the standard alt-azimuth mount the stars will rotate during your exposures, causing them to become streaks.  I have two discussions of equatorial wedges on this site, a general discussion about the value of a wedge for visual observing and a detailed discussion on heavy-duty wedges for astrophotography.  However, some new software now available, allows you to stack a series of short exposures and combine them to yield a good image, and this software is allowing astrophotographers to take good images with Alt-Az-mounted scopes, thereby obviating the need for a wedge (see the Using a Webcam for Planetary Photography page for more information).

Regardless of which photography system you choose, your life will become much easier if you purchase a flip-mirror system.  It’s a mirror-diagonal that holds both a camera and an eyepiece, and allows you to switch your view between them by flipping a mirror up or down.  It is used to center the object in your camera and to help you focus it. Achieving focus with a camera is extremely difficult, and a flip-mirror system takes some of the pain out of the process. (Note that you will probably still need to guide your scope during the exposure and a flip-mirror won’t do that - see the Guiding an SCT page on this site for more information). One nice flip-mirror feature is that you can leave it on your scope for visual observing, and use it for photography as well. Murnaghan Instruments created the first flip-mirror.  They sell a flip-mirror for 1.25” eyepieces (shown on the left) for $100 and a 2” version for $600 (and they also sell other telescope accessories).  The Murnighan Instruments flip- mirrors can be adjusted to center the observed object in both mirror orientations. 

The flip-mirrors sold by Meade are also adjustable. The Meade flip-mirror for 1.25” eyepieces, Model 644, sells for about $150.  The Meade product allows you to adjust the focal point of both the eyepiece and the camera to be the same (making them “parfocal”), within limits. Note that Meade asserts that the Model 644, which is equivalent to a 1.25” diagonal, may cause vignetting when using a 35mm camera and I have found that indeed it does (and the Murnaghan 1.25” Flip-Mirror presumably would as well). But it’s not so much a problem if you are shooting the Moon with 35mm film and a f/6.3 focal reducer - the Moon fills most of the 35mm frame but not enough that vignetting is a problem; and, the Moon is a good subject for beginning astrophotography because it is bright enough that exposures are short, so tracking accuracy isn’t a problem (although good focus always is). 

If you plan to use 35mm film for deep-sky objects however, you should get a 2” flip mirror such as the Murnaghan or the Meade Model 647 flip-mirror system (shown on the right with an illuminated reticle eyepiece at the top, and a CCD camera on the back of the flip-mirror system.) It is equivalent to a 2” diagonal and sells for about $250.  Note that if you use your SCT extensively for both visual observing and astrophotography, another reason you may find it useful to go for the more expensive 2” flip-mirror is because you can use it with 2” eyepieces (as well as for astrophotography).

Books on Astrophotography

A book that provides a good list of deep-sky objects to photograph is Jess Gilmore’s The Practical Astronomer’s Deep-Sky Companion, which I describe on the Books page.

The classic book on 35mm film astrophotography is Astrophotography for the Amateur, by Michael A. Covington, Cambridge University Press (Second Edition, 1999).  It provides a wealth of information on basic techniques. It does focus* on 35mm film photography much more than CCD photography, but it’s still the primer you need to become familiar with the basic issues. Note that Covington posts updates and corrections to his book on his Web site.

Another, newer book on film astrophotography is Wide Field Astrophotography - Exposing the Universe Starting with a Common Camera, by Robert Reeves, Willmann-Bell, 2000. Although the Covington book described above is a modern classic, Reeves’ book is also excellent and either one is a good reference on film astrophotography.

CCD camera images contain a lot more information than will be apparent from the raw image displayed on your computer monitor, because they capture a far greater brightness range than can be displayed by your monitor (or can be seen by the human eye or captured by 35mm film).  Extracting the best image from the raw data takes knowledge and experience.  So if you are considering CCD astrophotography, immediately get the Handbook of Astronomical Image Processing by Richard Berry (a former chief editor of Astronomy magazine and a pioneer in CCD astrophotography ) and James Burnell. It is published by Willmann-Bell, Inc., a company that is dedicated to publishing books on astronomy (although not particularly to good customer service in my experience).  It is an excellent, very detailed treatment of CCD images and how to process them to extract the best final photograph from the raw data.  This book will save you hours of learning time. (It also comes with an image-processing program, AIP4Win, written by Richard Berry. Although CCD cameras typically come with their own software, Berry’s is probably more sophisticated and in any event is useful for practicing the image processing techniques described in the book.)  This book is rather expensive ($80 with shipping) but the included software is excellent and most commercial CCD imaging software applications cost a lot more by themselves, than does this software plus the book.

There is an older version of this book - Introduction to Astronomical Image Processing - which is much less detailed and technical. It includes an old DOS software image processing application which isn’t all that useful , but you may find this book easier to get your arms around and it is lower priced.  However, in the long run you will be better off with the newer book described above.

Another book available for CCD photography is The Art and Science of CCD Astronomy, edited by David Ratledge, Springer-Verlag, 1997. But the whole area of digital astrophotography equipment is so fast-moving that the information in a 1997 book is somewhat out of date. Your best option is to get Berry’s book or keep current by perusing the Web regularly. Start with Sky & Telescope Magazine’s Astrophotography section

Good advice for film astrophotography is also contained on Jerry Lodriguss' Catching the Light site.
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* pun intended - if you don’t get it, you haven’t yet dealt with the difficulty of properly focusing an astrophotograph.
 

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