AZ mount vs EQ mount

[twelly27]

I understand that for taking pictures the best to get is an EQ, but I'd rather hold off as long as possible, as I don't really want to spend the amount of money I need to if I can get away with my AZ mount for the time being.

id like to know:

whats the longest exposure time I can from an AZ mount that will be a decent picture.

Is there a certain EQ mount I will need or will the EQ3 be a good choice.

can I add the syncscan and motors to the EQ mount as I'm new to it all and would prefer to still use it.

Any information on the above subjects and other info would be helpful. Thanks

Regards

Chris

[sgazer]

with Az mounts there are 2 issues affecting the length of exposure

1) the tracking ability - the are moving in both ALT and AZ to track, an eq mount is moving in RA only, which is easier as long as it's polar aligned. It will depend on what focal length you are using eg. on a typical SLT mount, you might get 1-2 minutes at 85mm or 30-60s at 250mm.

2) field rotation - where the stars rotate around the edge of the frame as the mount it not aligned to the axis of the earth, is not affected by focal length, but is affected by the area of the sky that it's pointing to. There is a map on the net somewhere, but in general; in the east/west/orng the meridian there's less rotation to 60-90s, in the north/south, there's more rotation so 20-30s.

Your choice of EQ mount will depend on the size and weight of what's going on it, whether you are doing visual or astro photography, whether you want goto or not and tracking (in one or two axis) or not.

[sgazer]

some field rotation info here;

http://autostarsuite.net/forums/storage/19/4981/field%20rotation%20v3.pdf

[twelly27]

I already understood the field rotation etc, was hoping that I could take more pictures at a shorter exposure and stack them, or a, I thinking that's abit too easy?

I suppose at a push I could forget the goto etc, I think I'll probably try to get to the shop I use and talk to the people see what they say

thanks for the info

Regards

Chris

[sgazer]

sorry, I thought you were after 'any information on the longest exposure time from an AZ mount', and I was explaining the reasons for the exposure times I suggested otherwise they would be meaningless, along with providing a link to calculated exposure times, but as you know that already, I'll just add that yes you can stack images also.

[dph1nm]

I happily do 30sec exposures on my alt-az mount (at 660mm focal length with a Canon 1000D). You can get pretty reasonable pictures of most of the Messier objects if you are willing to stack up to an hour's worth or so.

It is often forgotten that, without autoguiding, you may not be able to do much better on a cheap EQ mount (unless you are at a shorter focal length).

NigelM

[twelly27]

That's what I was thinking if I can get away with doing more shorter exposure and stacking them, I'm just wondering how long it takes for field rotation to effect things, or do the picture software etc fit it all right for you?

[Helen]

If you use deepskystacker it will compensate for the field rotation when it stacks. You'll end up with jagged edges, but a crop will sort that out :-) I'd say give it a go and see what you can achieve, that's the way a lot of us started and learnt how to process.

Helen