Double exposure question

[Vlad Soare]

It depends on what you're trying to achieve. For the picture below the correct exposure would have been 1/2s at f/32. Instead of making one 1/2s exposure I made 16 exposures of 1/30s each, at f/32.

Why 16 and not 15? I don't know. It depends on how you calculate. You can regard 1/30 as being 15 times shorter than 1/2, so you would need 15 exposures.
My reasoning was a little different. I thought that 1/2 and 1/30 were four exposure stops apart (1/4 - 1/8 - 1/15 - 1/30). A four stop difference means 16 times less light, so I made 16 exposures.

[sfjphotography]

Thank you for responding, I now have a better idea as to going about doing multiple exposures. The effect I'm looking to get is an image that is in sharp focus though has a blurred exposure over it creating a sort of glow around everything. I've done this digitally though never on film, so I was a bit confused about getting the exposure right without blowing the highlights out. thanks for taking the time to help me out.

[Vaughn]

I have done that...I believe I made two exposures at the normal exposure of one exposure. What is also important to the final outcome is how you throw the second image out of focus. One way to do it is to throw the second image out of focus by extending the bellow just a little. This will make the second image slightly larger than the first, besides just being out of focus.

What you will find happening will be the center of the image almost unchanged and as one leaves the center, there will be more and more displacement of the second image, relative to the first. The image might have a feeling of radiating out from the center.

Changing the f/stop (opening it up) for the second shot is another way and using the depth to throw the second exposure out of focus. With this technique one would have to be aware of which objects in the scene are not on the original plane of focus, as these are the objects that get the highlight glow. Objects on the original plane of focus will not have the "glow".

If I have time this evening, I will scan an example of the first technique and post it.

Vlad...I used that same technique for an ocean shoreline shot, catching the waves at different places for 16 exposures. Funny how the waves did not look very different from the people in your image!

Vaughn

[drew.saunders]

Why 16 and not 15? I don't know. It depends on how you calculate. You can regard 1/30 as being 15 times shorter than 1/2, so you would need 15 exposures.
My reasoning was a little different. I thought that 1/2 and 1/30 were four exposure stops apart (1/4 - 1/8 - 1/15 - 1/30). A four stop difference means 16 times less light, so I made 16 exposures.

Since the speed indicated by "30" is really (supposed to be) 1/32nd of a second, you got it right anyway. "15" and up lie to you. I guess, long ago, someone decided that people liked shutter speeds that ended in a 5 or 0, so 1/16th became "15" and 1/32nd became "30" etc. The old 1/25, 1/50 are really those speeds (assuming your old shutter is accurate, and it isn't), so I guess that's where the idea of ending all the speeds in a 5 or 0 came from.