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DPChallenge Forums >> Photography Discussion >> Need Help - Multiple Exposures
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06/01/2008 07:55:11 AM · #1
Hi everyone, I am starting to play around with impressionistic photography and want to create an image with many multiple exposures (between 20-80). I did some searching online for how to exposure each shot and then combine the photos digitally (Photoshop) but can't find anything that deals with large exposure numbers. Any thoughts on how I could do this?

Any help is greatly appreciated
06/01/2008 08:02:55 AM · #2
I tried the demo of this and was quite impressed .... //www.cs.ubc.ca/~mbrown/autostitch/autostitch.html
06/02/2008 10:45:23 AM · #3
I assume you mean multiple superimposed images (i.e. your camera is on a tripod, you take multiple shots without changing location or framing)?

The easiest way is to keep things to powers of two.

2 images - under-expose each by 1 stop
4 images - under-expose each by 2 stops
8 images - under-expose each by 3 stops
16 images - under-expose each by 4 stops
32 images - under-expose each by 5 stops
64 images - under-expose each by 6 stops

Mind you, you don't have to be spot on. If it was say 55 images, each under-exposed by 6 stops, you'd still have something usable, albeit (marginally) under-exposed. Similarly, if you took 80 images, each under-exposed by 6 stops, you'd still have a usable image that was slightly over-exposed.

If you want to get more precise about it, then rip out a scientific calculator. The number of stops you need to under-expose each image is given by the formula log N / log 2 where N is the total number of images. For example, for 80 images, the result is log 80 / log 2 = 6.32, so you have to underexpose each image by 6.32 stops. In the Windows calculator, you could get this by choosing the scientific view, then entering 80 <log> / 2 <log> =

Enjoy your experimenting! I haven't tried it with a digital camera, but I have done it on film with some interesting results. Make sure your tripod is quite stable (not affected by any breeze, traffic vibrations etc).
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