Considerations and calculations for stacking on LG format film
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Garry Edwards
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It's a very simple process, the important thing is to totally exclude all unwanted ambient light, which means that you must work in total darkness.
There are two distinct and discreet ways of doing it . . .
1. Use multiple exposures in order to create more power than a single flash can provide - 2 flashes = 1 stop, 4 flashes = 2 stops, 8 flashes = 3 stops etc. The shutter must of course be open throughout the process. The flash will be in exactly the same place throughout. The flash will of course be set to full power.
2. Use multiple exposures in order to create the effect of more flash heads than you actually have, in which case the flash head is moved between flashes, adjusting the power between shots as necessary. Start with the flash power at the lowest required setting, and increase it if necessary in different positions. You must do it that way round because, if you turn down the power between shots, the flash head may produce more power than that set on it.
There are two distinct and discreet ways of doing it . . .
1. Use multiple exposures in order to create more power than a single flash can provide - 2 flashes = 1 stop, 4 flashes = 2 stops, 8 flashes = 3 stops etc. The shutter must of course be open throughout the process. The flash will be in exactly the same place throughout. The flash will of course be set to full power.
2. Use multiple exposures in order to create the effect of more flash heads than you actually have, in which case the flash head is moved between flashes, adjusting the power between shots as necessary. Start with the flash power at the lowest required setting, and increase it if necessary in different positions. You must do it that way round because, if you turn down the power between shots, the flash head may produce more power than that set on it.
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- Ian Grant
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Doesn't work like that because of reciprocity, yes 2 flashes i just about 1 stop, but you need 5 or 6 for 2 stops,10 or 11 for 3 stops, the exact number will depend on the particular film used.
It's exactly the same with multiple daylight exposures as well.
Ian
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Yes, reciprocity failure is a factor, but not a massive one in my experience.
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How fast does a flash fire? Lets say 1//1000 of second? Seems you can pop off alot and easily hit 4+ stops before you hit 1 second or more total exposure
1 flash 1/1000
2 flash 1/500 total duration
4 flash 1/250
8 flash 1/125 duration etc etc
Is this not correct?
Ha writing it out actually looks about right, TIL!
1 flash 1/1000
2 flash 1/500 total duration
4 flash 1/250
8 flash 1/125 duration etc etc
Is this not correct?
Ha writing it out actually looks about right, TIL!
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Adjusting the power of a flash does not correlate to the length of each flash exposure, as you are assuming, it's the power discharged from the capacitors.
In fact the flash duration is the longest at high power, and shortest at low power, so the opposite.
Ian
In fact the flash duration is the longest at high power, and shortest at low power, so the opposite.
Ian
Garry Edwards
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Let's not go down a rabbit hole and take this thread off track - but what you say is only correct with IGBT technology flashes, the opposite is true with conventional technology ones.
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Almost all modern camera hot shoe flash guns use IGBT technology as do a great many of the newer monolites and flash packs, It's fairly standard these days,
Yes, one at 1/2 & 3 at 1/4.
Ian
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Do you mean two at 1/4 Ian?
Garry Edwards
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You're right when it comes to hotshoe flashguns, but as most of them only produce around 70j and LF cameras are typically used at around f/45, it didn't occur to me that anyone would want to use them for this purpose.
With studio flash (which sadly is the one subject that I know anything about) there are plenty of old ones in use, and over 70% of all new sales are conventional technology - most people want IGBT but have more sense than money, and won't pay the inflated prices.
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If your flash is IGBT, this might work, but you’d need low power settings. Because of recycle times
Which, if you’re simply popping them off to increase exposure, it becomes pointless.
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What are the ideas? I haven't done it with large format, but I don't see why it would be any different than with any other film camera (or digital for that matter). Large format does increase the amount of light you need for each exposure, but that's about it.
In the most simple form you can simply limit the flash's impact on the scene for each exposure (i.e. hard light and shadows), with the light illuminating the opposite area for a second exposure. Or just as simply, mask off the lens so that one area of the scene doesn't reach the film; and flip the mask for a second exposure.