Big toe ... Efke 25 test

I recently ran a film test with Efke 25 sheet film exposed at EI 25 outdoors in open shade and developed in (US) HC110 dilution B for 4, 6, and 10 minutes. I plotted the curves and got the results indicated in the attached thumbnail.

It appears to me the film does have a daylight speed of about ISO 25 but I've never seen such a long-toed film curve. Excuse the geekness, but while I haven't actually shot a pictorial example yet, I'd expect this film to have little shadow contrast but striking contrast in the upper midtones and highlights. I'm thinking this film is akin to the old Kodak Plus-X and might be great for studio portraits. Is that a valid assessment?

Has anyone else plotted test curves for this film? (I've seen the curve on the J&C site using a different developer.) Any difference in the curve shape with different developers?

FWIW, it looks like I'd get my normal CI of around .62 at 4 3/4 minutes @68F in trays with constant agitation using HC110-B.

Joe

The main Norwegian dealer of BW film and chemicals has done some tests too, and is doing more. Here's his curve for EFKE KB25 in Paterson FX-39: http://www.fotoimport.no/images/pk/FX-39-KB25.gif

Joe,

Could you please post a less condensed version of your curves image?

Thanks,
Lee

This is usually the type of curve obtained from emulsions using older technology, and yes Joe, you are right. There will be problems in some regions of the negative due to that curve. The straight line is not long enough.

If you compare this with any of the Ilford, Kodak, Fuji or Agfa films we like and consider acceptable modern films, they have sharper toes and longer straight line curves.

This is not meant to say it is a bad film, but it may be more difficult to work with under some conditions or with some developers.

PE

Does anyone have a curve for some modern films to post for comparison? Say Kodak Plus-X or Ilford FP4+? Or T-Max 100? I don't really understand what information the curves convey or how one determines from the curve what the contrast will be like, but since I've shot with the various films, perhaps I can relate it to my direct experience with them.

I really don't see the long toe that you speak of in your curves...maybe I am missing something. In fact when I compare the curve that you posted against Kodak TriX or Plus X they both have much more pronounced toes.

I have attached curves for Tri X and Plus X for comparison.

The curves for Ilford FP4+ and HP5+ also indicate a much more pronounced toe as well. (I couldn't copy their curves from their site)

It appears to me that the response of Efke would be much more linear throughout the curve then some other films.

SkipA said:

Does anyone have a curve for some modern films to post for comparison? Say Kodak Plus-X or Ilford FP4+? Or T-Max 100? I don't really understand what information the curves convey or how one determines from the curve what the contrast will be like, but since I've shot with the various films, perhaps I can relate it to my direct experience with them.

Click to expand...

Go here:

http://www.kodak.com/global/en/prof...f4018/f4018.jhtml?id=0.1.18.14.23.20.16&lc=en

and look for curves.

It has more than you ever would want about film curves and other film characteristics.

Enjoy.

PE

Here's an online characteristic curve for Kodak TMAX 100 developed in D-76 in a small tank:

http://www.kodak.com/global/en/professional/support/techPubs/f4016/f009_0438ac.gif

Notice that the curve is flat and then begins to curve upward at a certain point. That area represents the exposure threshold of the film and this threshold occurs in what is called the "toe" of the curve. With TMAX the toe abruptly gives way to a straight-line section which continues as exposure increases. Where the curve is an arc, contrast is low as any given change in exposure does not produce as much of a change in density as where the curve is a steeper straight line. In the straight line section, a given change in exposure produces a constant change in density and so contrast is constant. Since the average slope is also steeper there, the contrast is also greater there.

If you compare the TMAX curve to the Efke curve you'll see the TMAX curve toe gives way abruptly to a straight line section while the Efke curve has an extended toe (the curve is an upward arc) for a much greater proportion of the entire line. This means TMAX has more constant contrast throughout the entire range from shadows (the threshold area towards the left of the curve where it begins to rise from the flat straight line) through the midtones and highlights. The average slope of the TMAX curve in the middle portion is also steeper indicating greater contrast in that area.

Efke OTOH, has a long toe which is relatively flat but constantly changing until about the middle of the exposure range I tested. This means shadow contrast is very low (the curve is relatively flat) but it is constantly changing and increasing as more exposure is given until the midrange where it takes on a constant slope and contrast. As a result there is little separation of the shadows and low-midtones with the Efke film and a distinct increase in contrast in the upper exposure zones. TMAX has a more constant contrast throughout its entire range based on the curve shape.

As a result, I'd expect Efke to reproduce sort of murky shadows compared to TMAX given the same subject and lighting conditions. That could be useful though, such as in low key portraiture where any midtones and highlights would appear to sparkle relative to the extensive shadow areas.

Hope that makes some sense.

Joe

Donald Miller said:

I really don't see the long toe that you speak of in your curves......

Click to expand...

Donald,

The horizontal exposure scales are different between my homemade graph (zone exposure) and the fancy ones published by Kodak (log exposure in lux-seconds). Perhaps that is accounting for some of the difference in perception.

My Efke-25 film curve has an upward arc up through about a Zone V exposure. With TMAX, that arc gives way to the straight line at about Zone II exposure.

Joe

I downloaded the Kodak TMX in D76 curve, and then superimposed and scaled it as best I could to my graph of Efke 25 to compare curve shapes. I then traced one of the curve shapes for TMX and erased the other two that were originally on the Kodak graph. In the attached pic, the TMX curve is blue. I've put a T where the TMX curve begins a straight line and an E where the Efke-25 curve begins a straight section.

The TMX curve should actually be to the left of where it is because of its higher film speed. I made the 0.10 densities coincident between the two film curves at 10 minutes development times in order to better show the shape difference. The vertical scales were adjusted to coincide and I took a difference of 1 log unit exposure to be 3 1/3 stops when scaling the kodak curve to my graph. Sorry that the result is small and a bit fuzzy, but I think you can still pick out the curve shape differences.

Joe

It seems like you've got enough room at the top of the curve to rate it at an EI of 12 or even 6 for better shadow separation without shouldering.

David,

What I'm thinking is that this might be an interesting film for something like van dyke brownprinting or salted paper. With regular silverprinting, a negative density of about 1.45 above fb-f is usually where my highlight threshold to paper white is for an exposure of about Zone IX and 1/2. At EI 25 and a fairly short development time of 6 minutes, the Efke-25 film is giving a density of about 2.10 for that same exposure. For silver my guess is that I would have to lower both the EI and the development activity to fit on a normal paper.

Joe

For regular silver paper I use asa 12, for azo asa 6. I know this sounds slow, but its the only way I've been able to kick shadow values up onto the straight line portion. Other side of the coin is increased density, slow print times are the rule. tim

Remember that the final contrast of a print is the film contrast x paper contrast. Therefore, if the paper is 2.5 and the film is 0.6 the print is about 1.3 average. If the film in question is low then the print will be low. If the film has a very distorted shape, then the print will follow.

This involves differential equations to figure out the instantaneous slope of a given point on a print.

PE

Not only is the toe very, very long, but it is quite gentle. I think it looks something like the old Ektapan, which could be troublesome in uncontrolled situations. It's interesting to put a card across various sections of the curve and see the deviations from straight line from one zone to another. I'm not really sure what these mean, but over 3 to 4 zones, they are pretty consistent throughout the curve. That also shows that the curvature is pretty strong throughout the curve, not just at what we usually think of as the toe. Intellectually, I say "strong highlight contrast, poor shadow separation," but I'm not quite sure what it looks like. My experiments with the card seem to tell me that local contrast may be quite good over the entire exposure range. Any hints? Any actual experience? I agree that the paper would make a difference, and some experimenting with printing would be beneficial. Does the curve ar much with developer? Although it looks like an old-time curve, that doesn't mean it would be perfect for old-time processes. Many of those are quite linear (on log-log plots like we use). You would probably get old-time-looking prints. Experiment is, of course, the way to find out.

I use Efke 25 in Rodinol and HC110. I found I have to rate the film ASA 12 for both developers. For HC-110 I would increase exposure and use a weaker dilution, (I like 1:41). This should reduce the toe.

This is an example of Efke 25, rated at asa 12. 35mm shot with 28mm lens and heavy tripod. Developer was PMK pyro. Ilford postcard stock with dektol. Thought about a yellow filter for the sky, but figured it would block shadows too much. As you can see, shadows from the stand pipes are still pretty dark on the roof surface. Fortunately, they are small enough that in this shot it isn't a problem. The Efke 25 does a good job on the highlights, blending specular reflections on the metal surfaces into the softer metal shape. tim

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

Nice Tim. As you say, great highlight rendition. How long in the PMK?

Joe

Joe, sorry I didn't read this thread last year and respond. To answer your question, my "normal" time in PMK is 7:00 and uses the 1 minute initial agitation with 15 second cycles (one inversion) until completion.

Lately been using pyrocat-hd and minimal agitation with some success. Try 1:1:150 at 15 minutes for a "normal" scene, whatever that means. With pyrocat you can rate the film a bit higher than with PMK. tim