Why are Equatorial mounts better for AP

Started Nov 22, 2012 | Questions thread
RustierOne Veteran Member • Posts: 4,084
Re: Why are Equatorial mounts better for AP

RustierOne wrote:

JimP wrote:

If you were just interested in visual astronomy (the old eye up against an eyepiece), then the Alt/Az mount is very convenient. Simple to align new scopes with electronics.. just set it up, turn it on, aim at 2 stars and you are tracking the sky. Your scope will find and follow Jupiter all night long. Even though the field around Jupiter is EVER SO SLOWLY rotating, you won't notice and it doesn't matter. You can even do short exposure photography (under 30 second exposures) with negligible field rotation. Also, in Alt/Az mode, the eyepiece is always in a convenient location for viewing.

If you are serious about long exposure astrophotography, then, like the previous fine gentlemen noted, you'll need to switch to equatorial mount (or use a wedge on an Alt/Az mount). Then you can track for LOOOOONG periods of time and the entire field stays nicely aligned.

The downside of an Equatorial mount is that you have to closely align the mount to the polar axis and do an electronic alignment. Adds some tedium and time, although newer scopes have electronic assist for polar alignment as well (e.g. Celestron's All Star Polar Alignment). Also, the eyepiece can get into locations where a visit to a chiropractor is required the following day.

Clear skies,


Thanks, Jim.

Those are some good points worth noting by all. That last one explains why my back is sometimes out-of- wack after a night of observing.

I would add that with an equatorial mount not perfectly aligned to the celestial pole, the field of view will also slowly rotate around the center, perhaps even slower than with an alt-azimuth. And you're right about the convenience of alt-az on visual astronomy. It can be a lot less complicated than long exposure astrophotography and provide enough interest for a lifetime.

Best Regards,

It comes to mind that one area of astrophotography not requiring an equatorial  mount is lunar (and possibly planetary) imaging. Since the Moon is so bright, exposures are brief - field rotation is no problem. Even multiple exposures can be stacked with Registax to capture brief instants of good seeing. Registax can handle field rotation in the later versions. So even a Dobsonian mount can function quite well in this regard.

This was pointed out by someone in the Sony NEX forum (whose name I forget), before we had our astrophotography forum.

Best Regards,

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