Filter Factors for Efke 25
Hi everyone. After I worked out the reciprocity characteristics for efke 25 I thought I'd check out its response to filters. All filters were Kodak Wratten gels that I use most often in the field. As I suspected the manufacturer's factors cannot be trusted AND development compensation is necessary (at least with the filters that I commonly use). The filter number is listed followed by exposure compensation and then development effect (expressed in zone system parlance). Here are my results:
#47: 6x (+2 2/3 stops) N-2/3
#58: 4x (+2 stops) N+1/3
# 8: 1.2x (+1/3 stop) N-1/3
#12: 1.5x (+2/3 stops) N-1/3
#15: 1.5x (+2/3 stops) N-1/2
#21: 3x (+1 2/3 stops) N-1/2
#25: 4x (+2 stops) N-2/3
I hope you understand what I meant by development effect. All development times for my testing were N times. So with the #47 filter, N development gave me a negative as if I had actually given N-2/3. So if I were out in the field using say, the # 25 and N development were indicated, then I would have to give N+2/3 to get contrast back to N. If N-1 were indicated, then I would have to actually give N-1/3. If I actually gave the indicated N-1 then I would end up with N-1 2/3. Hope this makes sense! I'm beat....I need a cup of tea!
Filter Factors for Efke 25
I got some water boiling Andrew.. It'll take you 30mins to drive out here...
Filter Factors for Efke 25
Hi Andrew, "After I worked out the reciprocity characteristics for efke 25...."
Have you published your findings anywhere?
Thanks in advance, BILL Wm. Mitchell
Filter Factors for Efke 25
Hi Bill,
Yes, I published my finding here:
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=008bb4
Filter Factors for Efke 25
Wow. Talk about a tremendous amount of work to arrive at these factors.
Pardon me for being perfectly honest about a keep it simple alternative. I take out the filter I want to use and simply put it in front of my Zone VI modified Pentax meter and read the values for the exposure and go with it. This system has never failed me.
There are enought other variables with LF photography to deal with without adding to the check list unnecessarily.
Just a thought...........
Filter Factors for Efke 25
Michael: If your Zone VI meter reads accurately through a red filter you may have the only one.
Filter Factors for Efke 25
Reading through the filters has never worked for me. Applying a factor is more accurate once thorough testing has been done. Yes, there are a lot of variables but isn't it nice to be in control of as many of them as possible rather than the other way around? It seem like a tremendous amount of work but I believe that it refines my craft even more.
Filter Factors for Efke 25
I cannot remember the last time I opted for the rather stark view provided by a red filter although I have them in B+W for 95, 77, 67 and 52mm sizes. To be honest with you, it has been so long that I cannot say with certainty that a red filter has or has not been a problem with exposure, although I will test it shortly just to be sure.
I can vouch for the fact that all of my other filters function just fine through the meter. While I most certainly applaud your dedication to your results which , I just wanted to point out that there are alternatives.
However you get to your personal point of expression is what it is all about.
Cheers!
Filter Factors for Efke 25
Thank you, Andrew! I had just started wondering about this, with regards to the reduced red-sensitivity of EFKE PL25 (and R50). I know from experience that the filter factors for panchromatic film don't work too well with these films, so I really appreciate your effort.
Filter Factors for Efke 25
Can I ask your test methods? It seems that the quality of the light and the nature of the scene would have a tremendous impact on any sort of testing. The change in contrast that necessitated a change in development time would be totally scene dependent, wouldn't it?