Which CI & Calculating Flash Power for Transmission Tablet Contact Exposure
I am back from Wyoming, it was a wonderful treat for my eyes and for my soul. I am nursing 72 exposed sheets of 320TXP, a mixture of N-1, N, and N+1. Based on my earlier, flawed and flare-affected testing, described in this thread, and based on various recommendations here, I have treated N-1 as EI 160, N as EI 200, and N+1 as EI 320 (or 250 on a couple of sheets by mistake). Now, all I need to do is to figure out the corresponding development times, for XTol 1+1, to be able to print them on my diffuser (Ilford 500H) enlarger, with my usual papers, MGWT/MGIV FB.
As far as I can see from reading your detailed suggestions, bar Bill's post 41 which I have not yet fully followed, it would be good if I retested for the development times by contacting my 31-step Stouffer and so eliminating flare and other issues. I have just finished a marathon of reading other related threads, also on sensitometers, exposures when contacting and so on, and I am not sure if I would get reliably repeatable exposures by using my enlarger (equiped with Ilford 500H) due to lamp warm-up and start-up times with short exposures. Also, this light is a green/blue mix, not a white light, though this might not matter for this test.
My feeling is that I could use a Speedlight SB-800 in manual mode, checked with a flash meter (Sekonic L-508). I followed Stephen's 8 Feb 2009 calculations for the required contact exposures, on this thread, and elsewhere, but I don't know how to adapt those calculations to a flash exposure. My meter tells me a needed f/stop, and I do not know how this converts to the fcs or other measures of exposure at the surface of the contact printer. I don't mind doing some pre-testing to fine tune the exposure, but it would be nice to start in the right ballpark, and it would be a bonus to understand the math. I can vary the flash output and distance, and I know its various GNs.
My second quest is to figure out which CIs are the ones I should be striving for my N-1, N, and N+1. WBM clearly suggests some, but since they are based on the WBM technique for calculating them, I am confused if I should follow those. In fact, I am not even sure how to find out CIs from my new tests—other than by begging Bill again—since I have previously relied on Ralph's spreadsheet.
I suspect I will have to figure this over the course of trial and error, but I would love to give my new 72 sheets the best I can with the knowledge I have so far. Bear in mind, that until now, my previous few decades of photography, including 4x5 since 2000, were never based on testing but on manufacturer's recommendations, +/- about 30% for N+/-1, add-and-subtract some experience-based-factor for HP5+. However, I lack that experience with 320TXP. Overall, I like the idea of being more in control of the process, so if this stage succeeds, I will also test, for the first time, HP5+, to find out how it compares to my past experience.