Much of what I do also requires knowing the reciprocity factor for the film used. But Catlabs ain't going to give us that info. Omer has made that very clear, on this, and other forums.Originally Posted by Jim Fitzgerald
Much of what I do also requires knowing the reciprocity factor for the film used. But Catlabs ain't going to give us that info. Omer has made that very clear, on this, and other forums.
Isn't it best practice to come up with one's own reciprocity chart?
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
Wouldn't it be ideal to use the manufacturer's data as a starting point?
Naw, it's often off by a lot! Honestly, using reciprocity characteristics for a similar film is often just as good of a starting point as manufacturer's suggestions. If the film is all cut from the same stock, then get some roll film and do a few simple tests. Metering method and tools + development + lens characteristics + who knows.....will all have an effect on the results.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
I also have some films to compare and contrast. Pun
I will not write a review
I will say this, the CatLab outer boxes have no origin printed on the boxes
https://www.catlabs.info/product/clxf80ii
Tin Can
I have found Ilford reciprocity data to be very reliable and accurate for my needs.
Ilford used to show a single generic reciprocity curve in all of their data sheets. Starting around 2017 they issued new information, with an exponential formula and a separate parameter value determined for each film. The resulting curves were very different from those previously published, even though the films had not changed. For example, recommended corrected time for a metered exposure of 30 seconds for FP4 Plus went from just over 150 seconds to just over 70 seconds.
Howard Bond, a careful and methodical worker, had an article in the old Photo Techniques magazine reporting on results of his reciprocity tests of selected Kodak and Ilford films; his reported corrections were different from those provided by the manufacturers.
It's nice when the manufacturer can provide a starting point. But if one's photographic purposes require tight control, there is no alternative to running one's own tests even if only to verify that the manufacturer-provided data are reliable.
Oren I concur with your points above...that FP4 reciprocity is not nearly as "severe" as earlier charts suggest. Thing is though...with respect to any additional suggested changes to developer times (although Ilford is pretty relaxed about this), is to be very careful about this as reciprocity can also be a great tool for the contrast expansions often needed in otherwise "poor" (like three-stop EV range) lighting conditions. Loads of times in my experience...confronting minimal EV changes as the light was fading - I've reassured myself that "reciprocity (failure) will take care of this."
Good point, there are two sides to the reciprocity coin. FWIW, I use a standard development time regardless of SBR or reciprocity. But if one does tailor development to individual exposures, careful consideration of how to optimize for different long-exposure shooting scenarios is certainly a good idea.
I can reveal that around 2014 (I think) I began correspondence with Ilford regarding their generic curve and basically pestered them into testing and generating proper factors, which were eventually published. Having followed along as the work was done, I can say the revised factors are solid. I wish Kodak would have done the same.
At the time, Howard Bond's data was better than anything in Kodak's or Ilford's documentation, though I was not crazy about certain parts of his methodology (for example that he was using a Zone System framework. I still basically use Bond's adjustments for Kodak films.
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