alt-az mount tracking and long exposure

[mislav]

Hello, i am occasionaly imaging sky. I have alt-az goto mount. I am reading about long exposures and field rotation. Can anyone know would lowering one tripod leg towards polaris help? Ofcourse, its imposible to lower it about 20degrees, but.... anyone knows? i dont see point buying wedge-for that money i can buy eq mount...

[Thalestris24]

Hi

You really need a good quality eq tracking mount, that you can polar align, to do long exposure AP. I believe you can do short exposure AP with a alt-az mount. Probably limited to about 30secs (I've never tried it myself).

Louise

[mislav]

yes i know thats best and golden standard...but for now, i want to take all that alz-azt can give.. i was hoping to reach 60-90sec---

[happy-kat]

Depending where in the sky and what focal length you use then 60+ seconds can be done.

[Thalestris24]

Hi mislav

You can try and see  Some theory here http://www.jdso.org/volume7/number4/frey_216_226.pdf

Louise

[mislav]

22 minutes ago, happy-kat said:

Depending where in the sky and what focal length you use then 60+ seconds can be done.

i am on north 45 alt, scope is 150/750... shooting on every direction, but most of targets are south...

[kendg]

You can always try making one. Here is a good example for a Celestron. 

 

[SilverAstro]

Briefly ! : low in the west and east give best times, south not so good. At latitudes in the UK 20s to 60s or even 90 are ok ( depending on your criteria)  However, as the latitude decreases the available times rapidly decrease. Conversly, at higher latitudes they increase until (in the limit) you arrive at the pole when the alt-az magically becomes an Eq ( I suspect you already knew that ! )

The question now arises :- if you tilt your altaz a bit, as you suggest ( tell it you live in ummm ? Edinburgh !) I think it will mimic the high latitude exposure times.   As Louise suggests give it a go !   BUT I wonder if we would be limited to imaging only those objects above the horizon at the simulated location. From your location many of the visible objects would be below Edinburgh's horizon, SO would the mount track or balk !?

I think I might give that a try one day. Not heard of anyone doing it so I think there may be a fatal flaw somewhere

[happy-kat]

@kendg Celstron altaz mounts have an eq mode which means they can be used on a wedge. Skywatcher only have an eq mode option on the Virtuoso mount not the star discovery (as far as I know) which the OP has.

Your 150/750 is pushing the exposure time with that focal length but trawl back through the No EQ thread to see what others managed with a similar focal length.