I understand the difference between equatorial and altazimuth mounts, but German mount? Made in Germany or is this a different beast altogether?
Appreciate any comments on merits of different mounts for different kinds of astrophotography - lunar, planetary, nebulae, etc
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#1. "RE: Astrophotography mounts" | In response to Reply # 0nrothschild Registered since 25th Jul 2004Wed 12-Sep-12 08:51 PM | edited Wed 12-Sep-12 08:56 PM by nrothschild
A "German" mount is short for German Equatorial Mount, often abbreviated GEM or G.E.M.
The GEM is the classic equatorial mount.
Folded optics like your Questar often have fork mounts as an option and I suspect Questar more or less invented the consumer fork mount in the early '50s. Fork mounts are necessarily sized to a specific scope and usually there are integral fittings. In other words, fork mounts do not make good generic mounts that you might mate to any scope.
The other big problem with fork mounts is that the arms often create problems swinging the scope through. It's usually necessary to swing the scope fully upright to point at the pole in order to align the mount. This is particularly a problem with a camera. And forks are never large enough to handle refractors or Newtonian reflectors. They are always used with folded optics such as the Q or typical SCTs.
This is a particular problem with the Questar fork because it was sized for portability- a Q in its case with the motor driven fork mount will fit under an airline seat (I've done it). The price paid is that it does not make the best astrophotography mount. The Q7 fork is much larger, and can even accommodate some cameras but the Q7 fork mount alone weighs 30-40 Lbs. and is quite massive.
A fork mount is far cheaper to make than a German mount, probably lighter (after considering the GEM counterweight) which is why they are typically bundled with SCTs. And they are probably somewhat more compact for storage and transport, again after considering the counterweight and the need to transport and store a number of parts verses one big thing.
Alt-Az mounts are basically fork mounts that are not tilted to point at the pole. For photography the arms have to be long enough to allow your camera to point up, similar to the problem of pointing a camera laden scope at the pole when using an equatorial fork mount.
Alt-Az mounts, with computer guided servos, can be very simple to align to the poles. The mount is not physically aligned to the pole. The computer turns servos in both axis.
Alt-Az mounts suffer from field rotation unless the optical tube is turned in sync with the celestial movement or some optical wizardry is done. Field rotation is a problem with very long exposures typical of star fields and nebula (and all other deep sky objects but would not generally be an issue for planetary and lunar photography because the exposures are short, even when running webcam type video streams. Unless you do crazy long streams.
Some fork-like designs have a single arm. They are cheaper, lighter, and more portable. And less stable since only one side of the scope is supported. I would research stability issues carefully before buying one.
GEM mounts are usually designed to be generic, with various plates and clamps to attach the scope. GEMs tend to be rather heavy, especially when counting the counterweight, which often weighs about as much as the scope.
And if you are using a GEM for photography you often need a set of weights to tweak the balance as you add or subtract gear, including the camera. An out of balance German mount will tend to bind up the polar axis, causing tracking difficulties.
If I were looking for a general purpose mount with photography in mind I would strictly be looking at German mounts.
P.S. I have never heard the explanation of the origin of the "German" name. I just assume it was invented centuries ago in Germany.
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