Amateur Question on Long Exposures

[albert_richardson1]

I would add just a few observations:

The purpose of the long exposure times is to allow the earth to rotate enough to make a nice star trail. Pointing the camera toward the North Star will make concentric circles, and directly overhead & somewhat to the South will get straight lines across the sky. (I'm in the Northern Hemisphere.)

 

Expose the film for the stars not the sky. Reciprocity adjustment is intended to adjust low light scenes to make them brighter to read better on film. The advice given above to use trial and error starting with about a 5.6 f-stop is probably more helpful. This is actually the opposite of reciprocity adjustment. The intent is to keep the sky black in the picture even after a long exposure that would otherwise make it too light. The theory is that you really can't underexpose the black night sky.

 

Bulb setting originated when photographers used air hoses and rubber bulbs to trip their shutters. Squeezing the bulb caused the shutter to open and releasing it allowed the shutter to close again. Timed setting requires you to press the cable release to open the shutter and again to close it. Timed is probably more useful for the night sky. Set the camera on a good sturdy tripod and make sure that it is standing on a good footing. Adjust the camera for the part of the sky you want. Focus on infinity. There is really no DOF so there's no need to sight anything. Do everything possible not to touch your setup again until the photograph is finished once you open the shutter. Bumps and jiggles will show up in the light trails you get.

 

Timing to the second is not so critical with exposures that are many minutes long. If you don't mind having to lug something else along, an ordinary kitchen timer will probably do the job. You'll need some kind of small flashlight anyway.

 

To get stars over mountains, I think I would set the camera with the mountains at the bottom of the frame around sunset so I could still see clearly enough to get the composition right. I would wait until the twilight sky makes them look right and take my first picture. Then I would adjust the exposure for the night sky without moving or jarring the camera and wait for the stars to rise. Then I would take my starry pictures. I think I would put two pictures together for the finished image. The point of keeping the camera still is to get the pictures as perfectly registered as possible.

 

The whole thing would be a lot of fun. Have a great time.

 

BTW: Film SLRs usually will not take double exposures because the film advance lever cocks the shutter as it move the next exposure into position. There is no way to cock the shutter independently on the SLR cameras I've seen. I don't know about making double exposures with DSLRs. I think I would prefer separate exposures to try together later so that I would be able to select the combination I like the best without fear of ruining the whole project.

[mark_sirota1]

<i>Film SLRs usually will not take double exposures because the film advance lever cocks the shutter as it move the next exposure into position. There is no way to cock the shutter independently on the SLR cameras I've seen. I don't know about making double exposures with DSLRs. I think I would prefer separate exposures to try together later so that I would be able to select the combination I like the best without fear of ruining the whole project.</i>

<p>

Albert, almost every film SLR I can ever remember handling has a little button on the bottom plate which would temporarily disconnect the film winding mechanism from the winding lever. You press and hold the little button while winding, and the shutter will reset but the film won't move. Some of the more modern film SLRs have other mechanisms requiring you to go through the electronics; the Nikon F100 is one example.

<p>

Some digital SLRs will do double-exposures in-camera (the D200 is one of them), but it seems to make more sense to do it in post if you have the luxury of time.

[albert_richardson1]

Oops! Thanks Mark. I only ever used the button to release the mechanism to rewind the film. I hadn't occurred to me to use it to make double exposures!

[mark_sirota1]

Heh, it's been so long that I forgot that the button was also for rewinding the film!

[albert_richardson1]

It's been a long time since I used my old 35mm, too. I forgot that once you press the rewind button there is no way to engage the mechanism again except to open the back of the camera. This would double exposures such a nuisance I would use another camera altogether.

 

Incidentally, amateur astronomy magazines and books should have a lot of material and examples to help set up and make celestial photographs.