Accomplished imagers will say the CAT's mount is 90 percent of the reason for their success and that a prospective astrophotographer should plan to spend about 90 percent of an initial budget on the mount. That's true, all things being equal, but all things are not equal. If the goal is long exposure prime focus imaging, a heavy
R. Mollise, Choosing and Using a New CAT, 25
DOI: 10.1007/978-0-387-09772-5_11, © Springer Science + Business Media, LLC 2009
duty mount along the lines of (at least) a Losmandy Titan or an Astro-Physics 900 is very desirable. Unfortunately, these are in the $8,000 and up price range. They are also heavy as well as heavy duty. Don't imagine investing in a mount in this class or the next tier ($10,000 range), assures good results, either. Even with the best equipment, imaging is challenging, and the learning curve is steep. There is no doubt big German equatorial mounts make a new astrophotographer's teeth-cutting easier, though.
Are big-dog GEMs too rich for your blood? One secret of the deep sky imaging game is to make up for a less-than-heavy-duty mount by downsizing the telescope that will ride on it. Although a Losmandy G11 or Celestron CGE might not support a 14-inch SCT for hours-long exposures, they can do well with a 10- or 11-inch. If money is a real issue, even a humble CG5 can produce surprisingly good pictures with a 6- or 8-inch SCT.
How much telescope is too much telescope for a mount? The best guide is the manufacturer's stated payload capacity. These capacities are usually realistic for visual observers, but not for imagers. Expect to put about half as much weight on a mount as the maker recommends if picture taking is the agenda. For example, the CG5 is rated for 35 pounds. Halving that leaves a "practical" weight limit of 17 pounds. It's best to keep under even that, if possible. An 8-inch SCT at approximately 12 pounds is just right for a CG5. Also keep in mind that a CG5 or Meade's LXD75 might work well on a calm night but become useless for picture-taking in a light wind no matter how light its load. A good mount isn't just a requirement for long exposure deep sky picture taking, it's very desirable for Solar System imaging, too. Planetary photography requires high magnification to produce high-resolution images, and a steady mount is almost as important there as it is for two-hour deep sky exposures.
Is a German equatorial mount the only way to take pictures? What about the fork mount that came with the telescope? Imaging is generally considered easier with GEMs. They are easier to balance, less shaky pound for pound, and may track better than comparably priced forks. Not everybody shares this opinion, though; the fork has many fans among astrophotographers. There is no doubt a fork mount SCT can produce excellent deep sky images—hundreds of thousands have been done since the C8 debuted in 1970.
As mentioned several times previously, if a fork mount telescope is to be used for long exposure imaging, it must be set up in equatorial mode on a wedge. Not just any wedge will do for serious prime focus imaging. Those sold by Meade and Celestron are simply not sturdy enough for long exposures or easy enough to adjust to make precise polar alignment simple. Fortunately, third-party manufacturers such as Mitty Industries (Appendix 1) are producing after-market wedges that are more than up to the task of long exposure prime focus work. Probably one of the main reasons forks have gotten a bad rap for imaging is insufficient wedges. Even a C8 needs a sturdy platform.
One other weak link for both GEMs and forks is often the tripod. Both Meade and Celestron have improved their standard tripods over the years, but there's still room for considerable improvement. One thing some serious imagers do is adapt heavier tripods to their scopes. Meade's Giant Field Tripod, for example, designed for use with its 12-inch and larger scopes, can, sometimes with a bit of ingenuity, be used with Meade or Celestron 8-inchers and offers a great deal of improvement.
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