View Full Version : Filter Factors for Efke 25

Andrew O'Neill
5-Jul-2004, 23:23
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!

5-Jul-2004, 23:43
I got some water boiling Andrew.. It'll take you 30mins to drive out here...

wm mitchell
6-Jul-2004, 08:24
Hi Andrew, "After I worked out the reciprocity characteristics for efke 25...."

Have you published your findings anywhere?

Thanks in advance, BILL Wm. Mitchell

Andrew O'Neill
6-Jul-2004, 09:10
Hi Bill,

Yes, I published my finding here:


Michael Kadillak
6-Jul-2004, 09:22
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...........

Kevin Crisp
6-Jul-2004, 09:29
Michael: If your Zone VI meter reads accurately through a red filter you may have the only one.

Andrew O'Neill
6-Jul-2004, 09:44
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.

Michael Kadillak
6-Jul-2004, 10:06
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.


Ole Tjugen
6-Jul-2004, 13:51
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.

Dave Schneider
6-Jul-2004, 16:56
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?

Andrew O'Neill
6-Jul-2004, 17:21
Perhaps the quality, or rather type of lighting plays a part in this. For me it was all about a zone III placement in a scene recording as zone III regardless of filter being used. Shadows predominately have more blue light so you would thing that the use of a red filter such as the #25 would block lots of this blue light requiring more exposure. Hence the filter factor of 8x....but my testing indicated that that was too much compensation. 4x was adequate. My approach was first sensitometric, making in camera exposures of a sheet of film in my darkroom using a light balanced for day light. I used Gordon Hutchings' Zone Board idea as the target. After that I try it out behind my house. I shot the same scene under overcast and clear blue sky using my data and the negatives look and print very nicely. Seems like a lot of work but I've learnt a lot in a very very short time.