EFKE R25 Spectral Sensitivity & Red Filter

[doclagios]

OK, if you look at the technical data for EFKE R25 film at:

http://www.jandcphotography.com/efkedata.htm

My question is, what effect will a #25 red filter have with this film? A red filter will pass it's own wavelength, which this film is not very sensitive to and it will block the lower blue wavelengths. If you look at the spectral sensitivity chart for this film, this leaves just about the green wavelengths with some red and whatever blue isn't filtered out.

How would this look in landscapes in the sierras, for instance on a sunny day? Black skies, light evergreen trees, lots of contrast? Apparently only light within 500 - 600 nm will be hitting the film.

Would a #12 yellow filter be a better choice so as not to give pitch black skies?

What about close-ups of rocks and trees? I have read that shadows consists mostly of blue light, so a red filter would make the shadows thinner in the negative - no matter what the exposure, correct? After all if the red filter is removing the blue wavelengths, it doesn't matter how long one leaves the shutter open, the light from the shadows will not hit the film.

EFKE PL 100 is much more red-sensitive so light from 500 - almost 700nm will be hitting the film with a Red #25 filter on so more light will be striking the film overall - green and well into the red.

Is this correct or do I have this all wrong?

I am going out tomorrow photographing in the sierras concentrating on granite rock and I was wondering what EFKE 25 with a #25 red filter would produce if the full frame is just a well illuminated piece of granite rock. Will it enhance texture strongly or will the negative be too contrasty?

Thanks.

 

[127]

I don't have the data sheets in front of me, but #25 is a sharp cut red filter, so it should only be letting 600-700 through. Used with Efke 25 you're looking at some VERY long exposures, as you'd only be using the 600-630 band where the film isn't very sensitive in the first place.

A Yellow filter will (usually) let 500-700 through, so then you'd be basically looking at the greens. Given that Efke 25 is Orthochromatic you'd get the same effect as a green filter. An Orange would be 550-700.

I've been working on software to simulate some of this - if you'd asked in a few days I could give you some plots showing exactly the resulting spectrum.



On a related note, Ilford's spectral data is a little unclear - The data sheets show "sensitivity", but say that it's in response to 2850K light. Do the ilford sheets show sensitivity (in which case you mulitply by light to get response) or response to 2850K (in which case you'd divide by light to get the spectral sensitivity)?

Ian

 

[Doug Bennett]

I know this: I've found Efke 25 not to be a great film for landscapes with rock. Because it is orthopanchromatic, the attenuated red response made rocky landscapes kind of flat to my eye. In general, I just never got the hang of this film. YMMV.

I've never tried Efke 25 with a red filter. My instinct is that you'll be disappointed: you're filtering for a frequency band to which the film is less sensitive. I dunno. Try it and let us know. If it were me, I'd shoot some other type of film as well.

 

[c6h6o3]

Try a #15 deep yellow filter. It renders beautiful skies with Efke orthopanchromatic emulsions. If you have any foliage in the image, local contrast there will be enhanced.

 

[doughowk]

Just started using EFKE 25 & have tried both yellow & orange filters. The orange gives a high-contrast, almost surreal appearance (see image in my gallery), whereas yellow appears more natural - at least for driftwood, no rocks in Florida.

 

[noseoil]

Watch out for shadow values when using a strong yellow filter. It will push them down to the point where you may begin to drop into zone 1. Yellow is still the first choice with Efke 25 for skies and clouds. Without the yellow filter, skies can end up very bland and without substance.

 

[galyons]

In my initial testing of efke 25, I shot through #29,(Dark Red), #25,(Red) #22, (Red Orange). Given the spectral response, none produced desirable results, (unless one is looking for a black bear at midnight effect! ). I found #23, (yellow), produced similar results as a #25 on pan film.
I mostly use #21, (light yellow), adds some density to the sky, contrast on clouds, builds contrast between foliage and rock.

I love this film, but the spectral response requires some close attention.

Cheers,
Geary

 

[mikewhi]

(there was a url link here which no longer exists)

Here is a scan of a negative which is EFKE 25 taken of a rock face with NO filter. There seems to be plenty of detail and texture in the rock. Possibly shooting without any filter would be a better idea.

-Mike

 

[Tom Hoskinson]

Iagree, mike. I recently posted a scan of a medium format Efke 25 negative taken with no filter that shows a lot of detail and texture in the rock.

(there was a url link here which no longer exists)

 

[127]

OK - I'm home now, with data sheets, and I've run a couple of simulations!

Here's the response of efke 25, multiplied by a #25 filter.

Thats not good. The simulation doesn't take into account the lighting, or the subject (I don't have data for those), but if you measure the area of these curves, we've reduced the sensitivity by a factor of 12.

By comparason here's the same filter on hp5:

Here the sensitivity is resuced by about 6 - hp5's red resonse isn't that great, but it's still needs only half compensation that the efke.

As sugguested by others I tried a #15 yellow:

Now senisitivity is only reduced by a factor of 2.4 - pretty manable.

Of course of theres a lot of light in JUST the right bit of the spectrum, then these factors will change dramatically.

The Filter data I used for these is pretty accurate (and easy to obtain), but film data is much more rough - I had to measure the curves from the Efke and Illford data sheets. If anyone has numeric data, they can share that would be really usefull to me.

Ian

 

[mikewhi]

Hi Mr. "127" (btw, whatever happened to 000-126? We all know about 007)

I'm not that tecnhical that I could plot this, so I need help intrepreting the graphs. Are you saying that for the first scan with EFKE 25 that the only light passed thru the filter is the small area under the red curve that crosses over the 3rd and 4th section of the graph? All other light is either blocked by the filter or is not rendered by the film?

-Mike

 

[127]

Hi Mr. "127" (btw, whatever happened to 000-126? We all know about 007)

Well 126 died a horrible death sealed in a little plastic cartidge...

I'm not that tecnhical that I could plot this, so I need help intrepreting the graphs. Are you saying that for the first scan with EFKE 25 that the only light passed thru the filter is the small area under the red curve that crosses over the 3rd and 4th section of the graph? All other light is either blocked by the filter or is not rendered by the film?

Basically yes.

The white curves are the response of the film vs frequency. The vertical lines mark 400,500,600nm - the approximate divisions between uv,blue, green and red. Efke 25 doesn't respond to much above 600 (ie in the 4th section), as it's basically insensitive to red.

A 25 filter is the top red line, so if "white" (thats a whole other ball game!) light where to hit the filter, only the stuff under the curve would reach the film.

Combine those two lines and you get the lower red curve. That is the effective light which reaches the film and then actually has some effect on it. The area under the final curve is what matters, but for this combination it's not very big.

I compared the area under the original film curve, with the final curves area to estimate an exposure compensation.

However to do this properly you need to take into account the original light, which isn't exactly "white". Ideally you'd have a spectrum for the light, multiply that by the spectrum of the subject, multiply that by the filter, then by the film to give a final spectrum. Compare that with and without the filter, and you have a totally accurate exposure compensation.

Ian

 

[doclagios]

WEell, all I can add is that I took the same scene with a red filter on the EFKE 25 and then put in a holder with TMAX 100 and shot the same scene with the same red filter on. I will process them in a few weeks when I get back from my trip and see if anything usable comes out. If so, I'll scan the negatives and post them in the technical galelry for general interest, if any.

Thanks for your help!

-Mike

P.S. I guess the EFKE will come out very thin as I only gave 3-stops extra exposure for the filter. Hope the TMAX negatives are good because the scene was lovely, high altitude, sotrm clouds interesting hills in the foreground, sage brush, etc.

 

[noseoil]

Please post your results when the film is done so we can see. I don't use a red filter with Efke 25 and am curious about a side by side test showing the difference. Contrast may be a problem, but post it anyway if something shows up.

 

[fparnold]

Just out of curiousity, AA has a picture in one of his books of a deep conifer forest scene, with nice tonal separation on the trees and open shadows, shot using a 44A filter, which he says gives an 'orthochromatic' response. Would Efke-25 unfiltered mimic that look? It would make it an interesting woods, foliage, and jungle film in that case.

(I know, I know, order a couple of rolls and go find a pine tree to get a real answer)

 

[127]

Any Mac users out there intrested in playing with some software for plotting graphs like the ones I posted a few days ago? I've been playing with the software, and it's in a state where its now in a relativly usable form. It's still a bit rough in places (and could do with more data being loaded into it!), but it's starting to be fun to play with.

If you're interested, then PM me and I'll send you out a beta copy.

Ian

 

[mikewhi]

I have processed the EFKE 25 negatives taken with a Red #25 filter. I gave 3 stops more exposure for the filter factor.

The negatives look better than good. Lots of contrast and detail in the lower zones and the cloudy skies are great.

I"m very pleased with the way the EFKE 25 negs came out with the red filter.

I am developing the TMAX 100 negs next in Pyrocat-HD to compare with the EFKE film.

Prints in a week or two.

-Mike

 

[mikewhi]

Whew. I've processed a lot of 5x7 negatives so far. They're washing now. I really like the EFKE 100 negatives, too.

I'm gonna pop open a bottle of wine and have a glass or two while they wash.

Anyone want to join me?

-Mike

 

[mikewhi]

I'm up to over 50 5x7's developed so far. All EFKE film and a few more to go. Then on to the TMAX 100 5x7 in Pyrocat HD. Then the 8x10 EFKE and TMAX 100 and some rolls of 120, too.

Wine is still holding out, more bottles in the pantry if needed!

-Mike

 

[noseoil]

Mike, if you run out of film, do you buy more and then run out of wine? This is sort of like chocolate sauce and ice cream.

"Opps, I ran out of ice cream and have too much chocolate sauce left in the bowl, so I added ice cream. Now, I've run out of sauce for the ice cream so I'll have to add more and, oops, I'm out of ice cream again so...."

Still want to see the Efke 25 and 25 red filter prints when you get them done. I'm wondering if the filter is the hot tip for cutting down contrast for better control with this flashy beast of a film.

 

[hansbeckert]

KB14 is orthopanchromatic: intermediate between ortho and pan. It's that simple. A red filter will work, but the exposure increase will need to be a bit more than for typical pan films.

 

[mikewhi]

KB14 is orthopanchromatic: intermediate between ortho and pan. It's that simple. A red filter will work, but the exposure increase will need to be a bit more than for typical pan films.

What is KB14? I don't recognize that as a brand..

Thanks.

-Mike

 

[hansbeckert]

EFKE 'F' 'K' (FotoKemika, Yugoslavia) licensed the old Adox (Germany) formulas after Adox went out of business and sold their coating equipment to duPont to coat litho film. In other words, Efke 25 is the same product as the old Adox KB14. KB is German for 'Kleinbild' or what in English is 'miniature' or 35mm film. '14' is the old DIN speed number. KB14 was ASA20, not 25. KB17 was ASA 40, and KB21 was ASA100. I used all of these films 35 years ago. The only one worth a damn was KB14. The 40 speed and 100 speed films were very grainy for their speeds, and KB14 was not as sharp as Panatomic-X, though slightly finer-grained than the Kodak film. I quit using KB14 after a few years and starting using Ilford FP4 much more when it came out in 1969. The old DIN numbers are now the degrees in the ISO speeds.

DIN=ASA/ISO
14=20 (Adox KB14)
15=25 (Kodachrome II)
16=32 (Panatomic-X after 1964)
17=40 (Panatomic-X before 1964)
18=50/64 (Agfachrome CT18)
19=64/80
20=100 (Adox KB21)
27=400

 

[mikewhi]

Mike, if you run out of film, do you buy more and then run out of wine? This is sort of like chocolate sauce and ice cream.

"Opps, I ran out of ice cream and have too much chocolate sauce left in the bowl, so I added ice cream. Now, I've run out of sauce for the ice cream so I'll have to add more and, oops, I'm out of ice cream again so...."

Still want to see the Efke 25 and 25 red filter prints when you get them done. I'm wondering if the filter is the hot tip for cutting down contrast for better control with this flashy beast of a film.

Hi!

1) I NEVER run out of wine.
2) There is no such thing as "too much chocolate sauce". Just slurp what's left in the bowl then go get a refill of BOTH ice cream and choco sauce. Yes, you can have it all.

Here are some digital pictures of some of the EFKE 25 negatives developed in Rodinal. They are blurry, sorry, but they do show the contrast of the negs. My densitometer reads a DR of exactly 1.35, which sounds good for Azo. I'm looking forward to printing them. Some lack of local contrast in the foreground of the shots in the hills, but maybe some bleach can help that out.

I'll develop the TMAX 100 negatives next and post some pics of them, too.

For both, I gave a +3 stop exposure for the Red #25 filter.

-Mike

 

[noseoil]

Mike, they seem to have plenty of detail to work with. Of course the proof is in the pudding, but it would seem that they will certainly print well enough and hold a full range of values. tim