Unguided EQ vs. AltAz?

[chd]

How much difference in tracking accuracy would I expect to get mounting my CPC 800 on a wedge, but not guiding, vs. the alt-azimuth setup?

Should I wait to invest in the wedge until I'm ready to jump into a whole guiding setup, or is there reasonable benefit from the polar alignment by itself even without guiding?

[ronin]

As I assume the Alt/Az is unguided then the EQ wins as it is tracking across the sky correctly and both are unguided.

If you guide the Alt/Az then you still get field rotation so long exposures are still out of reach.

So the option is a wedge or a goto equitorial mount.

Not sure how good the CPC will be at long exposure AP.

[chd]

Yes, it's unguided either way, so I'm not sure whether I'll see much benefit from polar alignment on a wedge. At least I should have tracking errors from only one set of gears rather than two, so that should be some help. I'm just trying to get a feel for whether it'll be enough help to be worth it, or should I just wait until I can do real guiding.

[lensman57]

How much difference in tracking accuracy would I expect to get mounting my CPC 800 on a wedge, but not guiding, vs. the alt-azimuth setup?

Should I wait to invest in the wedge until I'm ready to jump into a whole guiding setup, or is there reasonable benefit from the polar alignment by itself even without guiding?

This is a pointless question, I am sorry to say. If you want guiding accuracy you either have to invest in a good EQ mount and then guide it or you have to spend the best part of £12000.00 or more on a 10 Micron mount of some sort and if the alignment is right, then you can expect up to 1800s unguided accuracy. AltAz mount has no guiding accuracy what so ever so there is no point comparing anything else to it.

A.G

[rowan46]

It will track better on a wedge depending on your polar alignment  but if you want to image without a wedge you are looking at stacking relatively short exposures and letting the software sort it out or using a field derotator but a good one of those is not cheap. In theory you could probably guide using an oag and derotator

[chd]

I'm okay with stacking shorter exposures, but for some of the fainter objects you just can't get any useful signal in 10-15 seconds. Stacking up a lot of zeros still comes out as zero. I don't expect multi-minute exposures to work in any case, but if I can get up to 60-90 seconds that'll make a big difference.

[dph1nm]

you just can't get any useful signal in 10-15 seconds. Stacking up a lot of zeros still comes out as zero

Not so - a photon is a photon. Provided you have the gain on the camera set so it gives at least 1 ADU per photon then you will collect as many photons in lots of short exposures as you will in one long one of the same total time. What kills you is read noise in the camera, as you get one dose of this for every exposure. To overcome this you have to collect more photons, which means  you end up observing much longer with shorter subs to get the same result.

Having said that, I image unguided on both eq and alt-az  - at 2" per pixel I can probably go 2-3 times as long on the HEQ5 as on my Nexstar SLT  (1-2mins as opposed to 30secs).  But 30secs subs is plenty to do most Messier objects.

NigelM