Efke 25 Reciprocity Test Results

Discussion in 'Black and White' started by andrew_o'neill, Jun 20, 2004.

  1. Okay. I tested the reciprocity characteristics of Efke 25 4x5 sheet film and I have to say that I was suprised at the results. Before I started the test I quickly searched the internet for any reciprocity characteristics listed for this film. This is what I found: 1/2 no exposure compensation required 1 sec give 1 stop (2x) 10 sec give 2 stops (4x) 100 sec give 3 stops (8x) No development compensation was listed with this data so I thought maybe Efke 25 doesn't need it (just like my beloved HP5+). My own testing indicated that it indeed doesn't. But, the above exposure compensation data was way off compared to mine. Mine is as follows: 1/2 sec no compensation required 1 sec give 1/6 stop 10 sec give 1/3 stop (1.2x) 100 sec give 2/3 stop (1.5x) How can my findings be so different I thought to myself? I decided to expose a sheet outside of the back stairs. I adjusted the metre's reading and placed the shadow under the 2nd step on zone III. That was 16 seconds. My data says that I should give an additional 1/3 for reciprocity. I noted that the wall fell on about zone IX and eventually made the exposure. I guess I should explain how I did my testing. I have a zone wall (inspired by Hutchings' zone board in his pyro book) in my darkroom. I made 1/4, 1, 10, and 100 second exposures of my zone wall. The aperture was only adjusted going from the 1/4 sec exposure to the 1 second exposure. For the 10 and 100 second exposures appropriate ND filters were placed in front of the lens. The 4 sheets of film were developed in pyrocat-HD, 5ml+5ml+500ml in BTZS for my normal time. The negative looks good and the shadow density under the second stair's step is zone IIIish. The zone IX density was very close too, indicating that development compensation is not necessary for this film. I only tested out to 100 seconds. Things could be different beyond that. I was under the impression that Efke 25 was an old school film requiring very hefty reciprocity compensation. Maybe it's an old school film but with new school reciprocity characteristics. It would be nice for others to pipe in with their reciprocity (gettin' tired of typing this word...) compensation data... I'll try and attach my test curves and a poorly scanned negative of the back steps of my house.
  2. Sorry, my curves aren't very neat! The curve on the left is the 1/4 second exposure followed by 1, 10 and 100 second curve. You can see that they are very close together and contrast appears to be constant. Here is a scan of the negative.
  3. Andrew, have to apologize for my 1st thoughts when I have seen your 1st table (without reading text above it...). Then I realized that you are not out of your mind, but that I'm impatient reader.

    Well, I'm using efke 25 film for a long time, in all formats (KB, R and PL - the last one just for a few weeks) and have never used such a long exposure compensation. As I can recall, the longest was some 20 or more years ago (in those time this emulsion was KB-14, 14 din) when I needed about 10 minutes instead of measured 3-4 minutes.
    In last 10 years, 1/4 or 1/2 EV compensation was quite enough for my night shots, now using KB and R 25 (and R-20 for short period of time, 20 ASA... Fotokemika switched lately to ISO numbers).
    As I'm relatively new in large format, for last year and half I have used only PL-100 and have bought large batch of efke PL 25 in 9x12cm just a month ago. Now, I'm on vacation with new camera, new film and new developer, so for last week, I'm in game (or joy:)) of testing those new stuff. Well, as I switched from Rodinal to Xtol right here in small and completely inadequate equipped apartment, I'm not in right position to bet on my test's, but giving tolerance of 10% (to temperature, time, dilutions) exposure compensation values are close to yours.

    And yes - it seams that Fotokemika have, in one moment, slightly changed it's best emulsion - in good way, I think. So, those huge differences in exposure compensation you have found on internet (and those have shocked me) might be for "old" efke.
    Of course, I can not be sure that Fotokemika changed old ADOX formula, but I see that this emulsion is different than those one I started with as kid.

  4. Thank you for this information! I have been doing quite a bit of night shooting with this film. Glad to see the curves are so tight. For my purposes they really don't make an appreciable difference.
  5. Andrew,

    Your data fits my seat-of-the-pants tests with some recently-purchased Efke ISO 25 roll film (120). I got good results with a 1/3 stop increase for an exposure that metered at 20 seconds. Developed in Rodinal 1+49.

    "Good results" means that the negative captured details in the range of light in the scene (about a 4-stop range, IIRC.)
  6. Continuing my love-hate (leaning towards hate) relationship with Efke 25 I am still trying to figure out a way to make a decent pinhole photography film out of it. I like to get exposure times of several seconds in daylight (more would be great but without waving a ND filter in front of the pinhole during the exposure, it's difficult to achieve). Mostly when I have shot longer exposures with Efke 25 I have gotten unusably thin negatives. (Same for Efke IR which needs to be rated at around ISO 1 for long exposures behind an 89b).
    This last time I tried rating it at 5-10 ISO with exposure times in the 4 sec range, then developed it in HC-110 1:47 for 15 minutes at 70F, agitation at 30 second intervals for the first 5 minutes and then two more inversions during the last 10 minutes, and I do seem to have appropriately dense and moderately contrasty negatives.
    I really hate Efke curl though. I don't know why I just don't start using Rollei or some other film.

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