Exposure Time Alt-azimuth

[Anubis]

Hi,

I had my first try at astrophotography last night

The images I got where rubbish, which is what I was expecting for my first attempt. But practise makes perfect as they say, and with that in mind...

I know a Alt-azimuth isn't great for tracking, but its what I've got. What kind of shutter speed will I get away with before star trails 'ruin' the shot?

This shot is one from last night, the colours appear fine but as you can see there are trails and a bit of camera shake

http://astro.bryanmansell.co.uk/images/astrophotography/tweaked/Perseus_1_small.jpg

The camera shake I will fix by locking the mirror up and using a remote, but I'd still like to get rid of the trails.

Thanks.

[Sam]

How long was the exposure?

[Anubis]

sorry lol, 30secs at ISO400

[barkis]

Looks as though the camera had a nudge too. What was the lens focal length?

The faster the lens you use, the longer the exposure can be 20 seconds should work.

Bear in mind also, that the nearer the pole you are, the longer you can expose, but not by a great deal.

You notice on deliberate star trails, that the further away from the pole the stars are, the longer their trails are, and this is even though the exposure time is the same.

Ron.

[Anubis]

I had the camera directly coupled to my scope, which should make it a 400mm f/5

[barkis]

Sorry mate, I don't know why I assumed you were using a lens on your camera.

You had the camera at the first focus of the 80mm f5 scope. I,m afraid at that focal length, you will only get about 3 seconds to 10 seconds before trails start to appear. The longer time is only possible at quite high declinations The shorter exposer is if you image stars on the celestial equator. You will need a driven scope on an equatorial mount to improve on this.

You should be able to get some decent starfields with a 28mm lens on your camera.

Putting it on the scope severely limits your options. Unless you are going for the Moon.

Ron.

[Beyond_Vision]

I have used my LX90 10" 2500m focal length scope in Alt /Az mode with exposures ranging between 20 seconds to 45 secs and managed to get some reasonable images. You will get some rotation between sub images but stacking software will take care of this and then the image can be cropped.

Regards

Kevin

[barkis]

I don't think Anubis's scope is driven Kevin, I don't think he will get 20 - 45 second from a static scope. He can try of course.

Ron.

[Beyond_Vision]

I don't think Anubis's scope is driven Kevin, I don't think he will get 20 - 45 second from a static scope. He can try of course.

Ron.

Yep I agree Ron his post doesnt say what kit he is using

[Anubis]

Scope is in my sig A Meade ETX80 goto.

[Cloudwatcher]

Can't really add anything to what has already been said by the other guys. You will certainly see an improvement once you use mirror lock-up and a remote release the absence of which,I think,accounts for the kinks in the in the tadpoles tails.

Just out of interest may we now the subject of the image?

Without most of the tails I get this image but don't know what I'm looking at. :?

Cheers

CW

Click as usual.

[Anubis]

It is part of Perseus. I don't have my Astro software on this laptop, but I think the top most blue star from memory was Pi Perseus. (It was the only star field that 1. Was not covered by cloud and 2. I could get my scope pointed to without the camera body hitting the mount. I hadn't realised there were screws to adjust the way the camera sits on the t-adapter so it was sitting a little skew-whiff and not as tight as it could have been.)

How did you manage to get rid of the trails? Did you just clone them out in photoshop, or did you use software that is smart enough to do it automatically?

Thanks for the responses by the way folks, much appreciated!

[barkis]

Anubis, I have to apologise to you, I have gone off on a tangent in my replies. I should have paid more attention. What Kevin told you in his post is quite Valid. If you can get some stacking software, you should be able to grab some decent Images. It takes Practice of course.

CW has managed to remove the trails from your image, which you indicated was in Perseus.

Ron.

[dph1nm]

This is a good site for sorting out alt-az exposure times:

http://www.skyinsight.com/wiki/index.php/What_is_the_Maximum_Exposure_in_Alt/Az%3F

NIgelM

[Anubis]

Nice link, thanks!