I'm not sure that long exposures are its forte especially (unless the point is "slowest film possible in order to make the exposure long"---but you could do that with a neutral density filter too), although as far as I remember it has good-looking reciprocity data. I think it would be a good film for your "kill the background" idea or for light painting, though.
Adox/EFKE 25 -the 25 in the name was the Tungsten speed, it had a Daylight speed of 40-50 EI which is the same as I used Tmax 100 at (50EI), in fact I exposed both the same and developed for the same time sometimes together.
So I never thought it was the slowest conventional film that to me was AP25 & later APX25, and also PanF
Ian is that also true of the 50 ?
(i.e. that the rated speed is tungsten and the "real" ei is closer to 100)
Efke 25 was unique - very long scale, relatively high contrast, very fine grain, orthopan sensitivity.
No other fine grained film had these characteristics. ACROS is about the closest. Pan F, but comparison,
is ordinary pan and has quite a short straight-line to the curve. And so-called micro-films are really soot
and chalk when it comes to the toe and shoulder, and often have poor edge effect. So I don't see any
direct substitute on the horizon yet. I still have quite a few rolls of Efke 25 120 in the freezer. I liked it
under strong lighting in the mountains. But you gotta be carefully loading it - it edge fogs easily.
Ian - I routinely expose Efke 25, Agfapan 25, and Pan F at the same speed (ASA 25) for PMK development. I expose TMX100 at 100. What on earth kind of developer are you using?
Jessops 50 = EFKE 25 (old 14)
Jessops 100 = EFKE 50 (old 17)
Jessops 200 = EFKE 100 (old 21)
This is the data for Jessops R50 (EFKE 25):
So as you can see EFKE recommended 100 ASA (EI) in FR24 developer with KB/R14 (now called KB/R25), however FR E24 was a speed enhancing developer like ID68/Microphen, and the lower speed 40 ASA (EI) was in FR 5 a fine grain metol based developer which gave a slight drop in film speed compared to ID-11/D76. So taking that into consideration it's no coincidence that Jessops were selling EFKE 25 packaged as a 50 EI emulsion.
I did my own speed tests back in the 1970's with KB14 and although I've switched to Pyrocat HD I still expose at the same EI, I mainly use PL25 in my Agfa Ansco 10x8.
Drew, I mainly used TMax100 before I switched to Pyrocat HD, and with some films I've found a staining developer gives me a slightly higher effective speed compared to Xtol, so I'm shooting Delta 100 & 400, also HP5 at box speed. Tmax films have been revised since I stopped using them (due to lack of availability).
If this isn't too much off topic, I would like to ask something about developing.
You speak of "speed enhancing developer" and "drop in film speed". This is a concept that I’m starting to grasp, but not yet fully understand the WHY of it (and that bugs me).
I can understand that any developer works differently and gives different results. So – to get (almost) even results i(n density and contrast )with the same type of film – one must adapt developing times accordingly the use of the type of developer.
But how does a developer enhance or drop a film speed? Is this a way of saying that – instead of increasing developing times – we overexpose the film to compensate the enhancing effect? I suspect there is more to it than that.
Somehow I have a feeling it has to do with the effective ISO (EI) of the film, the type of developer used and also the adagio: “Expose for the shadows, develop for the highlights”. I think it has probably to do with the chemical proces of converting silver during developing: higher speed in the first seconds (called: toe?), then a steady development for some time and then a suddenly drop in speed at the end.
But I can’t put my finger on it yet and that’s bothering me. I want to understand the concepts and thus test & improve my developing qualities (i.e. eliminating more variables like chance) into a standard process.
Like I really grasp the WHY of the concept of “Expose for the shadows, develop for the highlights” since a few months, so now I can explain it and use it in my upcomming tests with Ilford PF4+ in 4 different developers.
I’m a self-educated developer since 2001, but never learned the technical backgrounds (curves, chemistry).
So could you please tell me what you mean with speed enhancing or drop in speed?
(And yes: I should probably dig out and reread my copy of Ansel Adams book “the Negative”, but that is still in storage for now…)
Bert, in very simple terms.
A normal developer like D76/ID-11 should give you a good overall balance of fine grain, film speed (box ISO) and good sharpness with an excellent tonal range.
A super fine grain developer like Perceptol or Microdol X does this at the expense of film speed, usually just Metol based they need increased exposure to achieve the same tonal range, but garon is significantly smaller.
A speed enhancing developer like ID-68/Microphen gives a higher effective EI at the expense of slightly coarser grain and slightly different tonality.
So choice of film, say Pan F, FP4/Delta 100, or HP5/Delta 400 and then choicer of developer Perceptol. ID-11 or Microphen gives a wide range of possible combinations and of course there are others.
It's why people say find a film/developer combination and stick to it learn all the variables.