Question about mounts.

[Utwo]

Are the equatorial and alt-azimuth coordinate systems the same, except for the way they are aligned, geometrically? I mean, I know that RA is in hours while Az is in degrees, but if I were to somehow rig an Alt-Az mount so that its base was aligned with the celestial equator rather than the ground*, could it function much like an equatorial mount?

And if this is the case, why are equatorial mounts more expensive that alt-az mounts of comparable stability? Does it have to do with the need for a counterweight and all that?

*Purely hypothetical. Not something I'm planning on doing.

[JohnW]

Are the equatorial and alt-azimuth coordinate systems the same, except for the way they are aligned, geometrically? I mean, I know that RA is in hours while Az is in degrees, but if I were to somehow rig an Alt-Az mount so that its base was aligned with the celestial equator rather than the ground*, could it function much like an equatorial mount?

And if this is the case, why are equatorial mounts more expensive that alt-az mounts of comparable stability? Does it have to do with the need for a counterweight and all that?

*Purely hypothetical. Not something I'm planning on doing.

Yes, your thought-experiment would work, if your scope didn't tip over. Another way of thinking about this is that at the pole, an alt-azimuth mount would also be an equatorial mount.

The greater expense of EQs is partly the need for counterweights (at least if you have a German mount) but mainly it's that you have extra moving parts (so you can align to the polar axis), and these parts need to be solidly made. For your EQ mount to work properly, the alignment has to be fairly precise. An alt-azimuth mount can get away with a fair amount of slop and still work adequately, especially if you're not using goto or DSCs. An EQ which couldn't maintain its alignment would be nearly useless.

[ozark1]

Are the equatorial and alt-azimuth coordinate systems the same, except for the way they are aligned, geometrically? I mean, I know that RA is in hours while Az is in degrees, but if I were to somehow rig an Alt-Az mount so that its base was aligned with the celestial equator rather than the ground*, could it function much like an equatorial mount?

And if this is the case, why are equatorial mounts more expensive that alt-az mounts of comparable stability? Does it have to do with the need for a counterweight and all that?

*Purely hypothetical. Not something I'm planning on doing.

This is a description of a Poncet platform for a Dobsonian telescope. They are commercially available (just)

The couunterweight is only needed for the German mount as the telescope is mounted off-axis. Yoke and split-ring equatorials do not need a counterweight - unfortunately they are latitude specific and not commercially available.

[Dave Mitsky]

This is a description of a Poncet platform for a Dobsonian telescope. They are commercially available (just)

The couunterweight is only needed for the German mount as the telescope is mounted off-axis. Yoke and split-ring equatorials do not need a counterweight - unfortunately they are latitude specific and not commercially available.

JMI sells a line of split-ring equatorials known as Next Generation Telescopes. I've used a couple of them over the years.

http://www.jimsmobile.com/images/ngt125_w18.jpg

http://www.jimsmobile.com/data_ngt125.htm#Picture

Dave Mitsky