[SERIOUS]Exposure Time

I feel like starting some home project including my telescope, so here's what I have in mind:

I want to build a "bracket" to fit on the telescope which will basically include two motors. One along the X-axis, and one along the Y-axis. This is the relatively easy part.

The hard part will be to get the exact coordinates from the telescope. What I thought would be perfect would be to put a camera on top of the telescope which will capture the night sky. This will then be compared to a starchart on the computer which will tell me exactly where I'm looking at, and will give me the ability to "direct" the telescope to a different star / object / whatever the case might be.

The question I have is: I noticed that taking a picture of the night sky with "normal" exposure time yields no stars in the taken image. I f I leave the expose long enough, I eventually get a perfect image.

I know that this all depends on how bright the star is, etc... but what would be the nominal exposure time to yield just the perfect result? I don't want to get an image full of little white specs, but instead I just want to get the brightest of the stars, eg: Sirius, Canopus, etc...

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Originally Posted by BillGeek

The hard part will be to get the exact coordinates from the telescope. What I thought would be perfect would be to put a camera on top of the telescope which will capture the night sky. This will then be compared to a starchart on the computer which will tell me exactly where I'm looking at, and will give me the ability to "direct" the telescope to a different star / object / whatever the case might be.

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I have heard of this done before! From what I remember from a couple of years ago the people that did this used a small circular camera/device in a holder which was mounted on top of the telescope. The camera/device was then connected up to a laptop which was used to capture the image of what the people was looking at through the telescope. I am not sure how the camera communicated with the laptop whether it was via cable or by wireless.

You're seriously wasting your time. Use mathematics. All basic data can be retrieved from existing catalogs.

I'm in agreement with Max on this.

But in any case an exposure of 10 seconds will give you all the Naked-Eye Visible stars and also a few of the brighter non-NEV ones. Much longer than that and you'll end up with lots of unsightly noise in the images.

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Originally Posted by wossy

I'm in agreement with Max on this.

But in any case an exposure of 10 seconds will give you all the Naked-Eye Visible stars and also a few of the brighter non-NEV ones. Much longer than that and you'll end up with lots of unsightly noise in the images.

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I'll take Max's plan into consideration. I'll struggle a bit with the maths (judged from the link he included in his post) but I'll give it a shot in any case.

As for the exposure time, I actually found this page. Very informative.