Problems with photos

[zimzimma]

Hi peeps,

Just wandered whether you could help me. After setting up polar alignment(which seems to be ok but not sure)im getting terrible star trailing on photos. This is the third time I have attempted DSO's and its pretty much same result everytime. Im using a rather heavy Canon EOS10d which may be the problem because I have left scope tracking same object for hours still staying in centre of view. I maybe missing something on eqmod or my host program(Starry Night Pro 6)or it maybe that I havent got the mirror flip(?) setting on my camera turned on. I have enclosed my attempted picture of Andromeda its way off considering it was only a 30sec exposure. Hope someone can help. Thanks in advance.

Rich T

[faulksy]

some one will be along soon with some great help/advise

[Sam]

Are you guiding or this an unguided image? If it's unguided you'll probably find that polar alignment will need to be done by drift alignment to get it accurate enough. Basically the alignment has to be very near perfect or you will get significant tracking errors. Unguided on an HEQ5 you should be able to get good enough alignment to be able to take 90sec exposures without any star trailing. There's quite a few discussions in SGL about drift alignment - well worth a try if you haven't had a go already.

[Rustysplit]

Have you balanced the 'scope on the mount with the camera attached? You do seem to have quite excessive trailing for a 30 sec exp.

I don't think the initial mirror flip will make any difference on a long exposure. I have a standard eq-5 with ra drive only and with good p/a ican get around 60 secs unguided on a good night.

[ollypenrice]

I agree with the above. Do a drift alignment. This is my preferred tutorial on how to do it; Andy's Shot Glass - Drift Alignment for Amateur astrophotography,ccd, Neutonians and Refractors, amateur astronomy

Balance with everything ready to go and you should do a lot better, though an autoguider is the way forward if you get serious.

Olly

[rocketandroll]

You should be able to get 60 sec subs without drift aligning. I normally spend about 5mins max doing my polar alignment and have never had a problem with relatively short exposures.

It's definitely an alignment problem though by the looks of it, the star trails to the bottom right of the image are far worse than those to the top left... almost too much for it to be normal?

The mirror flip thing may also be an issue

What scope was this done with... and what oriantation was the camera to the mount?

Ben

[rocketandroll]

I've been thinking about this and looking at that pic for the last fifteen minutes or so and something occured to me...

There are two centers of rotation causing those star trails.

The main issue is caused by the scope rotating against the starfield as evidenced by the long star trails in the bottom right and not in the top left, I am guessing the RA axis of the scope is just off the top left of the image (ie: the image is inverted)?

I can't think of anything else which would cause that much of a difference in the star trails over such a small area, Polaris certainly isn't just top left of M31 so it isn't just miss-alignment and the stars moving against the scope causing that or they'd be fairly uniform.

That's what the second rotation is... the stars are all little arcs in the opposite direction to the main rotation... even the ones that haven't trailed much at all at the top left, they are all tiny, almost uniform arcs, just the ones bottom right are stretched by the other rotation.

I am still trying to work out in my head what could cause this... but the RA axis rotating at the wrong rate (possibly due to loading issues, possibly due to something else) is an option, coupled with a slight missalignment.

Either way, this isn't just a drift alignment fixable issue I don't think... if that were the issue then you'd have slight rotation in one direction I'd have thought?

Or am I talking complete rubbish?

:-)

Ben

[Dann]

If your using a polar scope to align before you do anything else it might be worth checking that its still nicely calibrated.

Centre Polaris and rotate the RA, it should stay in the middle. If there is any drift then it will need a little adjusting.