Monday, October 06, 2008

Of Telescope Mounts and Magnification

Ask any serious amateur astronomer and they will tell you that the best type of mount for any telescope is an equatorial one, and for good reason. An equatorial mount allows you to track once you have your item centered. Not only that, but they actually make the task of finding the object easier by means of setting circles. This is crucial for distant, faint objects. However, are they truly necessary if you are going after wide swaths of sky at lower power?

Probably not.
Nothing truly illustrates this better than my 114mm short tube Newtonian "Felix". This small scope has a focal length of just 500mm, an RFT or rich field telescope. Its primary mount is an equatorial, but it is used mainly as a "sweeper", looking for faint fuzzies (it has a very old fashioned equatorial mount at that, one that does not allow the scope to be rotated. That little feature causes problems quite a bit). Does this telescope really need this mount for what it's used for? No. To be honest, equatorial mounts for low power telescopes are actually more of a hindrance than help with low power/wide field telescopes. Unless you are taking images, they are probably completely unnecessary.

Where, than, shall we set the threshold for mounts?
For my purposes, low power is anything less than 40 power (and I seldom exceed that). For most, though, the threshold might be as low as 30. Once you go past your upon threshold, an equatorial mount would probably be a better choice. Based upon my own experiences, I use the following criteria to determine which mount to use.

Alt/Az - "Sky sweeping", open clusters, stellar associations, nearby double/multiple stars, nearby galaxies, some lunar
Equatorial - Planets, lunar, double/multiple star, variable star, distant galaxies, globular clusters, distant open clusters

I prefer altitude/azimuth for a variety of reasons beyond the purely technical, though. They are much simpler and therefore require less setup time (which in the field makes a big difference). It might be harder to locate fainter, more distant objects, but with a little trial and error these can be located by starhopping. There are times, though, when an equatorial trumps these and is simply required.

For the casual reader, though, the choice of mount really depends upon a number of factors, many of them simply personal choice. I think that, really, is what matters most.

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