What ISO should I use for startrails photo? - 1

First off, I know about the startrails software to stack mult. Exposures, and this time I want to try to do it in one exposure.

Here's what I will be using:
-nikon d200
-18-55mm
-shutter speed: ~65 mins

My question is. What ISO should I use for this long of an exposure? When I use startrails software I shoot at ISO 6400, at 30secs each, but I think that might Be tops sensitive for 60 mins. I don't want to screw up this thing that will take this long to do, So could someone help?

Oh yeah, and I will be shooting after dark, so 11:00 and later.

Star trails… After dark? Yeah, usually the best time!
.
Digital is nice because you can shoot n look. Shoot n look. Adjust. Shoot n look!
.
Digital is also good because it does NOT have reciprocity failure like film.
.
http://en.wikipedia.org/...otography)
.
Now, as for a full 1 hour (or more) exposure… I have a modified Nikon D-200 re-built by Fuji called the S-5 Pro. It too can go for ever, it seems, for a time exposure. However, 2 problems set in.
.
1 - battery drain. I remove all batteries and use the 6v power supply (AC line current) that came with the camera.
.
2 - Heat build up in the CCD chip and noise building up. However, Fuji's Super CCD chip is EXTREMELY noise free here and it has a auto dark frame subtraction built in. The Fuji S-2 also has such a feature and is another excellent astro-photo camera.
.
Google - Dark frame - and - dark frame subtraction - for info and free software for such.
.
I would experiment starting at 400 for 15 minutes, then 800 and keep going up till I see noticeable changes. If you can go 60 minutes at 200, why not go 30 at 400? However, if the length of the star trails is what is wanted, and because the chip in the camera never slows down in gathering light, a ISO of 100 or 200 for the hour at 3.5 to 5.6 should give good results. A fast lens here, 2.8 or 1.8 is not needed for this long of a exposure because you WILL get sky fog unless your out here in the Arizona desert around Tucson or other dark places in the southwest.
.
My 55mm 1.2 lens can still only go for a few minutes tho before the sky fog of a gazillion stars starts to overwhelm things.
.
You sound like you have only 1 shot at this and not the ability to shoot over a few nights. What is wrong with learning as you go and gain knowledge here by trial and error? More than likely you are going to do things on your own anyhow, so keep a little journal of the times, settings, exposures, lens, etc… And do as countless thousands before you have done and get OJT here (on the job training).It's kinda like who wants to learn anymore when one can just ask to have the problem solved.
.

ISO 100

Bulb setting with a remote trigger

Aim at the North Star

The longer you keep the shutter open the longer the trails, which will spin around the North Star

It's the aperture that's tricky… Too small and not enough light from the stars will get through to register or too large and too much light pollution get's through and drowns out the stars

But even so it's really easy, and trial and error will sort it out

The battery will go flat quickly

Not all DSLRs can do Bulb or really long exposures, if the battery dies during the exposure you lose the picture as it isn't saved to memory card until after the exposure

The lower the ISO the better. I can't think of any reason to use an ISO higher than 100.

Usually ISO 100 at f/4 is ideal to allow starlight to expose film or sensors.

Also, if you are worried about screwing it up, try some test runs first.

Personally, I don't think a D200 is going to make nice exposures that long without some serious noise issues, but it is worth trying.

Reas this: http://www.danheller.com/star-trails