We briefly discussed night photography in our class a week or two ago. I am caught up on my assignments and would like to know how to get star streaks and circles. I have a wide angle lens and a 300mm zoom with macro capabilities. What would I use and what settings. I haven't got a cable release for my camera. Do I need one? (EOS ELAN 1) Also I seem to remember someone saying the circles need hours of exposure. How do you keep the weather from affecting your camera or battery? I live in florida so humidity and wetness are my concerns not cold. But I am visiting Michigan in the next month or so and would like to try it there too. Would I need to do something different there? Thanks, this looks really interesting.

-- martha goldsmith (oscar@unidial.com), November 07, 1999

Answers

To make star streaks, just point your camera at any area of the sky with a good population of stars and open the shutter on the B setting with a locking cable release. Yes, you will need one. Put everything on manual. Pick an aperture about two stops down from wide open. Shoot a number of bracketed exposures from maybe 3 minutes to 30 minutes.

For the circular star trails you need to identify the star Polaris in the tail of the Little Dipper. That is the celestial north pole, and all the other stars appear to revolve around it. A star finder (the circular cardboard ones) will help locate it. Put Polaris in the center of the field and make a series of exposures.

If you take your film to a lab you will have to tell them it is exposures of the night sky and the background should be dark, otherwise they will try to correct it and it will wind up a nasty greenish mess.

For more info try the Sky and Telescope Magazine web site: http://www.skypub.com/

It is pretty cold (25 degrees)at night here in the northern part of lower Michigan, so any camera that uses batteries will suffer. Best bet is to use an older SLR like a Pentax, Canon or Nikon that is completely mechanical. Electronic cameras use battery power to hold the shutter open and the batteries may drain on a long time exposure. If they do, they can hang your shutter, or close it or otherwise mess things up.

E-mail me and tell me what part of the state you plan to visit and I may be able to steer you to some good dark skies. Last night was great for observing from my area.

-- Tony Brent (ajbrent@mich.com), November 07, 1999.

Martha, it sounds like Tony knows what he's talking about. To add on regarding the trail length, etc., realize that the earth rotates once a day and the stars, by comparison, are in a relatively fixed position. If you point your camera straight up from the North or South Pole, the stars would seem to rotate about the center of your frame. At the other extreme, if you point straight up from the equator, they will all seem to go straight, not circling. The distance each star travels depends on the fraction of a day you expose, ie, for 1/10 day exposure (2.4 hours) they would travel 1/10 of a full circle.

Very roughly, with a 50mm lens, an exposure of about 30 seconds is about the point where "streaking" starts to show up. The key to proper exposure is in the aperture and the film speed. I can't give precise numbers, but roughly f/2.8 with about a 100 speed film will probably get you within a couple of stops. Are you aware of another Greenspun site where this is discussed further?

http://www.photo.net/bboard/q-and-a-fetch-msg.tcl?msg_id=000Ygb

-- Bill C (bcarriel@cpicorp.com), November 09, 1999.

Humidity is allways a problem - you can have foggy lens after 2 hours exposure at night. The answer is keeping the camera warm, warmer than the surrounding air. Many star photographers use electrically heated lens shades, but they are a little tricky to make and need big batteries. Easier is to take some suitable stuff, warm it a little in owen or on a radiator (do not make it hot, a little warm only) and keep it close the lens barrel. A longish plastic bag loosely filled with salt or sand will do, you can wrap it around your camera.

-- Sakari Mdkeld (sakari.makela@koulut.vantaa.fi), November 16, 1999.

There was a discussion on photo.net a while ago that discussed star streaks and what not. Go here to read it. Your choice of lens is going to be based on several compromises as to how long you want to the streaks to be for a given exposure time, how good your seeing is and thus the length of exposure you can get at a given aperture before sky fog sets in, how much sky you want in the image, etc.

One other hint. Take a well exposed, full frame picture of a gray card as the first exposure on the roll. It will give your processor a reference as to where the first frame is so they can locate the rest without guessing. I also tend to shoot slide film for color astrophotography so that I dont have to deal with a printer trying to print the image to a neutral gray level. I also use black and white film (hypersensitized Tech Pan developed in D19 is one of the best) and then I am in complete control.

-- Fritz M. Brown (brownf@idhw.state.id.us), November 16, 1999.