We got a great e-mail a few days ago. If we only had $10 for every time we got a cry for help like this ...







“I have tried and tried and tried to get images from the Brand X low-cost imager camera with my 12-inch SCT (I know they SHOW beautiful pictures on their website), but even after buying a new, faster, computer, I can’t get squat.”







Our reader went on to ask whether he should buy a $3,000 DSLR or high-end CCD camera to improve his astrophotos. Our answer ... Nope. Buy a different telescope.







The number of people seduced by the ads, and who end up buying a big Schmidt-Cassegrain as their first scope specifically to do deep-sky astrophotography is legion. They usually by-pass the portable and sturdier 8-inch models for the big 10, 11, or 12-inch scopes, thinking bigger must be better. They are going to get stunning images of galaxies and nebulas! And they are prepared to spend several thousand dollars, sight unseen, to do it. But what they get are underexposed, fuzzy and badly trailed blobs. So the answer must be spending even more money on a better camera, right?







Nope! Buy a different telescope.







OK, we’re not dissing SCTs. We own and use them ourselves and love them. We recommend them all the time to people looking for a great portable scope good for all kinds of observing, from planets to deep-sky. We do suggest nothing larger than an 8-inch for anyone who has to take the instrument to remote sites, or even just carry the scope to the backyard for each use — the bigger scopes are just too darn heavy and won’t be used.







But what we don’t recommend them for is deep-sky imaging. The same is true of the new “flat-field” designs from Meade and Celestron, and, for most beginners, even the Ritchey-Chrétiens made for imaging. Here’s why:







•The optics are too slow (at f/9 to f/10), requiring long exposures, demanding superb tracking.

•The focal lengths are too long (at 2,000 to 3,000 mm), requiring precise polar alignment and superb guiding.

•The long focal lengths will show up blurring from the poor seeing and wind most of us have to contend with.

•The fork mounts are often too bouncy, especially when tipped over on an equatorial wedge, and too hard to accurately polar align.

•Lower-cost German equatorial mounts, while easier to polar align, are often not sturdy enough for the demands of astrophotography, especially if loaded with a big aperture 10- to 12-inch scope. Nor do they have accurate enough tracking.

•The fields of classic SCTs are not flat, and won’t illuminate a large chip camera well, especially if used with a telecompressor, which usually produces a badly vignetted field.







If you really want to do serious imaging with a long-focal length Cassegrain-style scope (for going after galaxies) you need a superb mount, like the new Celestron CGE Pro mount (depicted above right). Now we’re talking $5,000 for just the mount. But that’s what it takes to support a big 3,000mm-focal-length scope well enough for long-exposure shooting. The astrophotos you are trying to emulate were likely taken with a big equatorial mount like this, not with a fork-mounted SCT.







All this advice is on page 291 of the latest edition of The Backyard Astronomer’s Guide. Turn the page and you’ll see an example of the kind of rig we do suggest for deep-sky imaging (it is also shown at right).







What we advised our reader was this:







Don’t spend $3,000+ on a super camera -- it won’t get you better results. Instead, buy a lower-cost DSLR (our latest recommendations are on the website here under Chapter 13) for about $1,000. Then spend the rest on a small apo refractor on a smaller, but high-quality equatorial mount (the Sky-Watcher HEQ5 Pro or similar Orion Sirius are great). This is more or less the set up we depict on page 293 and shown above right. Nowadays you can get several fine autoguiding options at low-cost and without requiring a big, heavy guidescope. The Orion package is shown at right. See Chapter 13 of our website for more recommendations.







But people just can’t accept that a little apo (like the Orion setup at bottom right) will get great deep-sky images. Don’t you need lots of aperture? No. You need fast f-ratios, and wide, sharp fields. Look at our astrophotos in the book — most were taken with small apos. They are great for clusters, nebulas, Milky Way fields and large objects like the Andromeda Galaxy. Yes, their short focal lengths (500 to 700 mm) aren’t ideal for small galaxies and planetary nebulas, but there’s a lot you can shoot with them. The short focal lengths and smaller, lighter telescope mean:







•The scope is less demanding to guide.

•Seeing conditions aren’t as much of an issue.

•The mount can be smaller, cheaper, and easier to set up.

•Apos (though usually requiring a field flattener) are great matches for DLSR cameras, providing sharp, fully-illuminated fields. DSLRs work great for all kinds of imaging, unlike specialized “deep-sky imagers.”

•And if you tire of astrophotography you still have a first-class portable scope and mount great for visual use that will complement any big-aperture reflector you might buy later. And you have a good all-purpose camera!

•All are ideal traits for a beginner astrophoto outfit.







Seduced by the ads? Or swayed by the advice? Take your pick!



— Alan Dyer





