 Thomas R. Simpson |
Long Exposures Revieled I would like to do many types of long exposures, now my better sens tells me that if I do long exposures of say 10/1-10/30 I should have to stop down a lot and even then it wouldnt be properly exposured, how do I do long exposure shots and still maintain proper exposure, and details and all details would help me out. Thanks
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robert G. Fately |
Thimas, if you are thinking about an exposure one month long (10/1-10/30) then you are correct - it just won't be possible. Unless you are shooting in an unlit cave, no film is insensitive enough to light to take that long to expose at any aperture. In any event, to answer your question of proper exposure: if you are familiar with the relationship of f-stop to shutter speed, then you know each is set in a "halves and doubles" sort of arrangement. Thus, if you shut down the aperture by one stop you can compensate exactly by slowing the shutter speed by one "click". For example, an exposure of 1/125th second at f2 provides the exact same amount of light to the film (or chip) as exposures of: Now this calculation will work until the so-called "reciporcity effect" is hit with film - that is, if the exposure is going to be longer than about 30 seconds or so (depending on the particular film) you need to over-compensate as it loses some sensitivity at that time range. I don't think the same holds true for digital, though CCDs can become quite "noisy" unless chilled to very low temperatures if used for long exposures - this is why astronomical cameras are cooled with liquid nitrogen or other exotic systems. Of course, 30 seconds is a long way off from 30 days, so again, given how I am interpreting your question, I don't think there is a way to do it.
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Thomas R. Simpson |
Bob, not a month long exposure, though I have wanted to do a two week exposure inside a cave, or at least thought about doing it. The shutter speeds I placed down are 10/1, or 1 second, or 10/30, or 30 seconds. And as for reciprocity failure, I have one data sheet that tells me the corrections for speeds from 10/1 (one second) through to 10/3600 (1 hour). My question is really... Say I want to do an exposure of 10/30 while there is still light out say towards midday, my common sense tells me that its not possible. But I have seen some exposures done before with it. How is it possible that the photographer acheived this, and what is it they did?
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robert G. Fately |
Well, the only aproach is really to use ND filters, since after a point smaller f-stops create diffraction distortion (that's why you don't see f64 available on your 50MM lens). You could concievably stack ND filters (as long as you're not using a wide angle lens where vignetting could come into play) but you probably should get the best brands (like B+W) because each additional filter will bring along soe flare and distortion potential of its own. Sorry I didn't recognize your nomenclature - I don't understand what 10/30 means and why it equates to 30 seconds. Obviously the 30 is the second count, but what's the 10 for?
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Thomas R. Simpson |
Thanks for replying back. You know, I have no idea. I learned it from reading up on the schwarzschild effect and decided to adopt it because to me it seems a faster way to write my long exposure shutter speeds. Dont know to be honest.
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