Efke 25/50 - to filter or not to filter?

All,

I've got some Efke KB25/50 to play with, but have been wondering whether or not using a filter is wise...

I got these films specifically because I liked the "old-fashioned" orthopanchromatic rendering. It looked like my first try, using a B+W 021 (light yellow) filter, with the suggested Rodinal / R09 time of 8 mins, was underexposed. I did compensate for the filter factor, however, I wonder if, because the film's spectral response is not the same as modern film, whether or not I have to also add extra exposure if using a filter to compensaste for the spectral response?

As an example, the Adox CHS25 ART (Efke 25) page here suggests has a good blue response into the UV. On P61 of the B+W catalogue available here, there appears to be a signifcant fall-off in transmission at 450nm if an 021 filter is used - with a medium yellow 022, the fall-off is even more pronounced.

Hope that makes sense. I know of course that there is nothing to prevent such a filter being used, and I found several threads discussinmg the subject, but my question is whether it is desirable if the "look" of the film is to be retained. Would using a simple UV filter to remove haze be a better idea? What does the film look like if a yellow / orange filter is used? Is a good alternative developer something like Paterson/Adox FX39?

Thanks for any help / pointers!

I would simply do a series of shots with and without the filters at different ISOs on my meter to nail it down (with the appropriate notes). My yellow filters take light away no matter what film is used, but each camera I own w/ an internal meter has it's own idea of just how much light that might be. Which is why I favor a test w/ each camera to see for sure.

momus said:

each camera I own w/ an internal meter has it's own idea of just how much light that might be.

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Is this valid also for SLR with TTL metering? I´ve always wondered that and tried to be generous with exposure when using filters, but never run a test.

It's not Orthochromatic just slightly less red sensitive than most films, I wouldn't worry too much, I've shot with EFKE 25 since the early 70's when it was first produced in Croatia.

Ian

From my experience the Efke films work well with all color filters except red. With yellow and orange you get normal effect. With red, you have to start compensating for the lower sensitivity. With green and blue you obviously don't need to worry much.

Ahhhhhhhh, I did know Efke KB25/50 were orthopanchromatic films rather than true orthopan - d'oh! Edited my original post.

Actually, Mauro35 / momus brought up the reason that I asked the orignal question where I should also have been clearer - the exposure was being read through the filter. Hence why I thought that the meter might have become confused as I am certain the shots are underexposed. I've never experienced the same issue with other films.

I'll do a test with an external meter to see what happens. Is it preferable to have even the light yellow filter to retain more of the "normal" look of the film, or does it just depend on what look is desired? I usually use a yellow filter as a matter of course for haze reducetion and a bit of contrast but have no problem, using none, or a UV.

James1 said:

Ahhhhhhhh, I did know Efke KB25/50 were orthopanchromatic films rather than true orthopan - d'oh! Edited my original post.

Actually, Mauro35 / momus brought up the reason that I asked the orignal question where I should also have been clearer - the exposure was being read through the filter. Hence why I thought that the meter might have become confused as I am certain the shots are underexposed. I've never experienced the same issue with other films.

I'll do a test with an external meter to see what happens. Is it preferable to have even the light yellow filter to retain more of the "normal" look of the film, or does it just depend on what look is desired? I usually use a yellow filter as a matter of course for haze reducetion and a bit of contrast but have no problem, using none, or a UV.

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It is all about the color wheel. If you use a yellow filter, yellow colors will be brighter, and purple colors will be darkened. Adjacent to purple is blue and violet, which will be darkened also but to a lesser degree.

If you use an orange filter, orange colors will become brighter, as will the colors adjacent to orange, which are yellow and red, but to a lesser degree. The complimentary color blue will be reduced the most, while green and dark blue will also be darkened, but to a lesser degree.

If you use a red filter, red tones will be lighter, and so will violet and dark orange, but to a lesser degree. Green is the opposite (complimentary) color, which is the one that will be darkened the most, while adjacent colors light blue (turquoise) and light green will also be darkened, but to a lesser degree.

It is all about the color wheel, the color of the filter, and its complimentary/opposite color.

With the Efke 25 and 50 films, the film is less sensitive to the dark red, so when you use that filter green colors will still be darkened, but the red colors will not be brighter to the degree you'd normally expect. It isn't the best combination. I'd stick to green, blue, yellow, and orange with these films.

The TTL meters (CdS) are normally oversensitive to red and near infrared. It is simpler using a hand held and adjusting the ISO on the hand held x2.

That way there are less variables.

For critical work shoot nominal and an extra stop.

@ Thomas - thanks for the concise explanation. I've seen much of that info in different places but not put together in a good understandable way.

@Xmas - aha! The meter on my camera is a CdS one, and I would not be surprised if that is the reason my photos were underexposed.

I tested efke 25 years ago and it has an interesting response to certain filters. I believe I posted the results somewhere here... if not, I can dig up my notes and repost it you like.

Andrew O'Neill said:

I tested efke 25 years ago and it has an interesting response to certain filters. I believe I posted the results somewhere here... if not, I can dig up my notes and repost it you like.

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I for one would like to see it.

Here is a link to filter data I posted 10 years ago at the LFF...

http://www.largeformatphotography.info/forum/showthread.php?10503-Filter-Factors-for-Efke-25&highlight=andrew+o%27neill+filter+factors+efke

Development compensation is also given.