man, i totally wish it did. great idea.
no the C330's are the RB67's of the TLR world, chunky, featured, and awesome. no darkslide though. however when i'm next in the darkroom i'll try that out, with a better meter on the reversing exposure that way too.
Paper Negative Reversal Process
It does work on FB, but there was some staining that I couldn't solve. When you look at what the paper is going through it isn't surprising, at least to me. Don't let that stop you from trying, that was just my experience.
Originally Posted by SMBooth
The Process Analyzed
I went to the darkroom this afternoon and put some time into getting a better idea of what's going on with the reversal process, and how to try and optimize the results. For this round of tests I essentially tried to replicate the conditions that have worked in the past for me in my bathroom, and intend to further experiment in a controllable fashion rather than just guessing and checking.
This is what I came up with today. Developer was Ilford Multigrade at 1:3 dilution. Paper was some old Kodak Multigrade RC II. I set up the enlarger without filters, using a 50mm f2.8 projection lens (for speed and the size of the projected circle). The picture above shows all the stuff I exposed, first a test for max black, then the smaller strips on which I tried a nine stop exposure range. The larger strips were a dialed-in five stop exposure range in 1/3 stop increments.
For this test I began quantifying my exposure in lux-seconds to have a universal unit of comparison for the different exposure intensities between the much slower and smaller intensities which create the negative image, and the short intense exposure which induces the tone reversal.
A close-up of my results, and the development information for the big strips. As you can see, the process is sensitive to changes in pre-flash development and flash duration/intensity. My feeling is that a slightly lower developer concentration might provide better overall contrast range compared to the results I achieved today. Also, I'm curious about what, if any, effect a shorter and brighter (but same lux-second) reversing flash would have.
I can post my complete exposure data if anyone is interested, but it will likely be quite different for other paper/developer combinations. My estimations of about 0.2s flashes for the self-portraits I posted earlier in the thread seemed to produce the best results today (I calibrated the enlarger to match the measured brightness of the light at counter-top distance). Maximum black on the test strip, both negative and reversed, was achieved at ~32 ls exposure, minimum reversed density (2 stops less than max negative black) at ~ 10ls, and max reversed density (starting 1.67 stops than min rev density) at 3.2 ls and less. The reversing exposure was 64 ls for the nominal 0.2s exposure at a measured 7 EV, twice the amount of light to produce max black.
Thoughts? Comments? Criticisms?
edit: looking carefully, as I hadn't yet today--I struggled to get these tests finished with a migraine coming on, which I've only now come clear of--test strips 4 and 7 have a reasonably large difference in development and exposure times, producing very comparable and good results. As with my earlier feeling, this procedure does have a fairly wide sweet spot.
Last edited by andy_k; 12-06-2012 at 06:50 AM. Click to view previous post history.
Alright, another go 'round, looking to see the effect of changing developer concentration in conjunction with variations in exposure.
The exposure range for these strips was from 2.5 ls to 12.5 ls (the 10 ls zone still the lightest after reversal) in 1/6th stop increments. Reversing exposure the same, other than where indicated. The first six strips were developed at 1:4 dilution, with the seventh at 1:5.
it appears to me that developer concentration has a similar effect to shifting exposure/development when push or pull processing on film; there is an inherent compromise between tonal range and tonal contrast.
it seems that at these very high developer energies/concentrations that the relatively small variations in exposure have a smaller overall effect, and need to be within a narrower range, than developer concentration.
Any input? I'd love to know what Photo Engineer might say about any of this, or anyone with more technical knowledge than i have.
Hey again gents (and ladies?),
Quick feedback from my experience using powerful flash heads to stimulate the reversal process: it makes a huge difference. Without really having numbers to relate to the above information, or surviving visual (scannable) results to give you, I noticed a massive increase in overal tonal range and contrast using studio strobes to hit the negative image with.
The reason I don't have anything to show you to prove it is a result of my recycling of fairly old fixer in my portable paper-picture kit. Having long since dissolved even the aluminium off of the bottle seal, and smelling strongly of ammonia, the fixer somehow bleached the developed positive images from very nice looking black and white to a creme and rusty brown. No idea what was going on there, but sadly the great reversal results were lost.
Anyone else try out my approach yet? Particularly with a larger format camera?
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I haven't tried it but I've been reading with interest these past weeks and hope you keep relating your experience! Neat idea to try to get this process under control.
It appears that a functional EI of 25 produces really great latent images that are very suitable for reversal, provided that your scene is illuminated with only 2 - 4 stops of luminance range. Reversing with a very powerful strobe is unquestionably the superior method, compared to bright halogen light.
I suggest giving it a try if you're interested, see what happens.
yeah, not sure if you saw my earlier posts but this is exactly it. the second exposure that i'm doing is not a fogging exposure in a chemical reversing process, but a solarizing exposure that i'm trying to control. the higher EI rating for the paper is just something that i'm estimating based on my test results as a more suitable latent image for my solarized direct reversal process (it's all done in one development, the paper never leaves the soup).
Originally Posted by johnielvis
i'm now quite done catching up on badly overdue darkroom projects, but as time permits me in the coming months i'll be attempting some ultra large format macro reversal images. i'll update here in the thread as progress is made.
I'm looking forward to reading them... I find this fascinating and hope to play with it myself eventually.