first time sky portraits

Dear Astrophotographers,

I'm heading out to Chaco Canyon in NW next week for a little deep sky/deep cold observing. I'd like to bring along my Nikon manual camera and tripod and try my first wide-angle sky portraits. I have a 35mm lens, hmmm, speed I can't recall at the moment.

I have Kodak Ektachrome 100-speed slide film. Does anyone have any ideas as to how long I should expose? Should I bracket (I guess there's little chance of actually "overexposing," right?)

And what's the upper time limit to avoid star trails?

Also how does potential cold (around 0') effect exposure time?

Thanks for any advice you might have.

doug

I have Kodak Ektachrome 100-speed slide film. Does anyone have any ideas as to how long I should expose? Should I bracket (I guess there's little chance of actually "overexposing," right?)

And what's the upper time limit to avoid star trails?

If you want to avoid star trails, then with a 35mm lens I would guess 30 seconds will start to show trailing. 20 seconds should be OK. No risk of sky fogging with that short an exposure.

Also how does potential cold (around 0') effect exposure time?

Shouldn't matter. Because you're using a manual camera you don't have to worry about the cold affecting the batteries, either.

I have used ISO 100 Kodak Elite II (really Ektachrome), and had it pushed to ISO 400 (2 stops) when processing. That was several years ago (1998) so I don't know if that's recommended with the film you are using. Perhaps others with more experience can comment.

Good luck,
Doug

Reeves' book gives the following unguided exposure times for trail-free images. These assume you're 30 to 60 degrees declination. They're shorter if you're closer to the equator, longer if you're closer to the pole.

28mm lens: 50s
35mm lens: 40s
50mm lens: 25s
85mm lens: 15s
135mm lens: 9s

Most lenses will show some spherical aberration at the edge when wide open, so consider stopping the lens down 1 or 2 stops.

Good luck.

sf

Go here

http://www.astropics.com/

And see what you can do with your camera. follow Wally's techniques--all very simple, just open up the shutter for a minute or so, and light things with a flashlight-- and see what happens.

Alex