Hello my friends,
I am of late in the unfortunate position of beginning to doubt everything I thought I knew about exposure regimes following a string of bad luck with my latest shots.
I do the majority of my work on VRP-M, not because I find it superior to any other film, but instead because I am just used to it (or thought I was).
I have been in the habit of exposing my VRP-M in the range of 40-50 µjoules/cm² for transmission holograms, which puts my film at a nice medium gray in the developer. When I was doing reflection work, I was in the 80-90-100 µjoules/cm² range for a good dark black in the developer...
Lately I'm beginning to realize that these numbers are but a mere fraction of what other guys like to hit their film with! I've seen some numbers that blow my mind (you know, 800 µjoules/cm² and so forth)...
It of course makes perfect sense that different films will have different properties and behave in their own way, but I would have thought that silver halide would play its game in a smaller ballpark, and my usual numbers wouldn't sound so ridiculous compared to what other fellows are doing.
I get holograms with my routine, but I'm concerned that they may be weak-sauce images compared to what I could be getting with much heavier exposures.
If this post inspires a thought, please jot it down here and lemme know.
Thanks, guys
Energy density thread
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BobH
Energy density thread
I've always heard the rule of thumb to be "overexpose and underdevelop". Your exposure energy depends on the processing scheme you use, and your method of evaluating density. I never evaluate density by eye, in the dark, with the clock ticking, with the plate still developing. Instead, I do the processing by the numbers, watch for evidence that something went wrong, evaluate the result after drying, then adjust the numbers if necessary for that particular film and procesing scheme.
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Justin W
Energy density thread
I think I need to come up with a technique for gauging my optical density before bleaching. Just holding my film up after the developer wash and seeing "how dark it looks" sure leaves a lot of room for error.
Some time ago I thought up a cool invention for measuring the OD of my freshly-developed film. It involved an infared LED and receiver that would tell me how much light was being transmitted through the darkened film. Dave B. tells me this gadget already exists which is disappointing but saves me a lot of money on drawing the patent
The fact that one can overexpose and underdevelop leads me to think that it less important how hard you hit the film than it is how dark it goes afterword...
I unfortunately have no frame of reference as far as optical densities are concerned. In fact, this term was entirely foreign to me until I started learning holography.
And so we're left with questions: About what optical density range are we talking for my "medium gray"? Does that sound to you experienced guys like roughly OD1? Slightly less?
What is the OD of film developed opaque? (Just for a point of reference)
What is the optimal OD for a transmission hologram? Which generally looks like what after development?
Sorry about all the goofy questions but I'm just feeling lost lately...
Respect to all who are trying to help me
Some time ago I thought up a cool invention for measuring the OD of my freshly-developed film. It involved an infared LED and receiver that would tell me how much light was being transmitted through the darkened film. Dave B. tells me this gadget already exists which is disappointing but saves me a lot of money on drawing the patent
The fact that one can overexpose and underdevelop leads me to think that it less important how hard you hit the film than it is how dark it goes afterword...
I unfortunately have no frame of reference as far as optical densities are concerned. In fact, this term was entirely foreign to me until I started learning holography.
And so we're left with questions: About what optical density range are we talking for my "medium gray"? Does that sound to you experienced guys like roughly OD1? Slightly less?
What is the OD of film developed opaque? (Just for a point of reference)
What is the optimal OD for a transmission hologram? Which generally looks like what after development?
Sorry about all the goofy questions but I'm just feeling lost lately...
Respect to all who are trying to help me
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Joe Farina
Energy density thread
If you go to Photographer's Formulary, and use the search term "step wedge" you will find several nice, inexpensive ones. Whatever you get, just make sure they are "transmissive" step wedges (i.e., you look through them at a light source to see the density).
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Justin W
Energy density thread
Step wedges? Neat.
Are these some sort of device darkened to a predetermined OD with which one can visually compare their film?
I'll go check that out.
Are these some sort of device darkened to a predetermined OD with which one can visually compare their film?
I'll go check that out.
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Joe Farina
Energy density thread
Yes that's it, those transmissive wedges are stepped (and labeled) with varying levels of OD. I think that's exactly what you need.Justin W wrote:Are these some sort of device darkened to a predetermined OD with which one can visually compare their film?
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Justin W
Energy density thread
Yes, thank you Joe. Sounds like a handy thing to have in the darkroom. I appreciate you bringing their existence to my attention.