wschwetz
Does anyone have any advice on the development of an APX 100 (with an exposure of 160 ISO) in Promicrol for a mixed-light enlarger (G=0.7)? Digitaltruth, which usually specifies times for condenser enlargers, lists the data on the bottle, but there’s no mention of contrast. By what percentage should the development time be extended to achieve a higher contrast?
zensusa
Hi Winfried,
I develop at 24 degrees in a rotary processor, but you can convert the figures.
My data relates to Retro 100 / roll film (equivalent to Agfa APX 100) with a 2-minute pre-warm, developed for split grade . So mixed light.
Promicrol 1:14 for 6 minutes 45 seconds at 24 degrees on rotation.
If you’re developing at 20 degrees with a 30-second tilt without pre-warming (which isn’t actually necessary with APX!), you should develop for about 10 minutes 30 seconds (possibly even 15 to 30 seconds less).
Good luck
Lothar
wschwetz
Thanks for your reply. Digitaltruth specifies 11 minutes for an exposure at 160–200 ASA; this is also stated on the bottle, without specifying the exposure time or the resulting contrast. Wouldn’t the exposure time need to be a bit longer to achieve a higher contrast?
zensusa
Hello Wilfried,
Your question **‘Shouldn’t the time for the higher contrast be a bit longer?’** cannot be answered as such, as the specific conditions (details regarding the Promicrol bottle or Digitaltruth) are not known.
The fact is that the rotation time I specified, 6.45 minutes, is a time I have tested myself using my own equipment, i.e. a time I have used in practical application. In other words, subjects with a normal contrast range (f5) result in a filter value/gradient of 2 to 3 when using roll film for enlargements up to a maximum of 30x40cm on Forte Polywarmton or the equivalent ADOX. The initial value of the developed negatives lies between 0.65 G and 0.7 G.
I have converted this rotation time for you using the well-known Ilford time table and the formula for ‘development movement’ – in this case, my rotation time divided by a factor of 1.3 times 1.4 (conversion factor for 30-second agitation). This gives a result of around 10.30 minutes for APX exposed at 160 ASA.
I’d simply start by developing using this value or the 11 minutes from Promicrol; that will give you a practical starting point. Incidentally, my experience with Promicrol shows that in quite a few cases the times are too long.
Incidentally, there are countless sources of error and deviation, even if you use the same ‘values’ that other photographers use successfully. I’d like to show you a typical example here using my own equipment.
I develop in a Jobo CPA2. This processor has a built-in thermostat. Generally, I develop at 24 degrees. But now for the surprise. My calibrated, highly accurate main digital thermometer, a GTH 175/PT from Greisinger (which I always use as a guide), shows exactly 24 degrees, yet the Jobo thermostat only needs to be set to around 21.5 degrees. As a safety measure, in case the digital thermometer should fail during longer processes, a standard analogue angle thermometer for black-and-white processes is also suspended in the water bath. This thermometer displays a third temperature, namely 23 degrees. The conditions are identical for all devices. As you can see, the temperature/thermometer aspect alone involves variations that can have a significant impact on the result. If you now also consider differences in the stirring rhythm (some stirrers are busy bees, others are sleepyheads :-), inaccuracies in the measuring devices, and so on, you’ll see that the specified values, even if the initial data is precisely defined, can only be approximate. In most cases, however, this is still a good starting point.
Until then,
Lothar
wschwetz
Thanks, I’ll try the recommended 11 minutes for now. Does it make a difference whether the films were made in rather grey weather or in sunshine?
zensusa
Yes, Wilfried, it does make a difference whether you’re taking photos in sunshine or in grey weather. However, the extent to which it affects contrast, gradient, etc. also depends on the subject. This is a complex topic, though, and as you don’t seem to know very much yet about black-and-white film development, contrast control, and so on, I’d recommend you take a look at the ‘courses’ in Schwarz-Weiss magazine. They’re available as PDF files. You can find them here:
http://www.schwarzweiss-magazin.de/
I think you’ll find everything there – free of charge – that you might still need to know to develop your films perfectly.
Best regards
Lothar
Wolfgg
Why do so many people struggle with this? From a technical point of view, the path to a top-quality negative really boils down to just two things: how do I *develop* my film so that the characteristic curve matches the contrast of my subject, and how do I *adjust the exposure* so that the subject falls within the right part of that characteristic curve?
If I were a camera shop owner, I’d hang this sentence up on the wall in big letters, and only those who can recite it from memory would get any film :rolleyes:.
Regards, Wolfgang
wschwetz
I had a look around the website and read what it says about contrast. Unfortunately, I didn’t understand most of it, despite trying things out. What I did learn – somewhat surprisingly to me – is that ISO sensitivity decreases as subject contrast increases; for example, you can shoot at 400 ISO in poor weather and at 200 ISO in sunshine. And film manufacturers (and developers, for that matter) provide no information on this (unfortunately not even for ADOX films). There’s nothing about this in the books I’m familiar with either. I’ve also learnt that there are no data collections on this subject, and everyone is constantly reinventing the wheel, laboriously trying to obtain the necessary data through test series – without changing the test conditions. (Is that actually necessary? In the age of digital, it’s not exactly an incentive to take up analogue photography. Personally, I don’t want to go digital because I don’t want to be sitting in front of a computer as well when pursuing my hobby). If you’ve now exposed a roll of film under different conditions (sunny yesterday, cloudy today), the adjustment no longer works; what’s the solution then? Practical rules of thumb would generally be helpful.
In my case, I’m ‘lucky’ enough to have had one whole roll exposed under heavy cloud cover and another in sunshine, both at 160 ASA. In the sunshine, I probably should have used 100 instead? But now it is what it is. What do I do now? Since Promicrol is a film that increases sensitivity, shouldn’t I be able to compensate for this with the sunshine film by conducting longer development?
Wilfried
CapitanoPiccolomini
Don’t despair, Wilfried. If you can put the recipe for a sponge cake into practice, then you’ll enjoy developing negatives too.
Most of the black-and-white enthusiasts who post on forums are like Shaolin monks who’ve already reached the umpteenth chamber of their temple.
So start as simply as possible: standard film (e.g. HP5), standard developer (Rodinal, HC 110) and get advice on exposure and development times for this combination.
Klaus (who started out as a street-fighting kung fu expert and still is one)
Wolfgg
Wilfried: Why not just use a few centimetres of film for a test? Choose a subject with a similar contrast to the shots on the film – for example, simply the view from your window – and take five photos of it (i.e. five identical shots). Then go to your darkroom and, in the dark, cut the exposed section of the film into three pieces. Develop the first section for the time stated on the bottle, the second for 30% longer, and the third for 70% longer. Then make a test enlargement of all three streaks on standard grade paper (or on variable contrast paper without a filter) and see which enlargement you like best. That will give you a very good indication of which development time suits your equipment best.
Regards, Wolfgang
wschwetz
Wolfgang,
I followed your advice, but I don’t find the results particularly enlightening. I took the photos in bright sunshine, so there was high subject contrast. The result: at 11 minutes (as on the bottle) there was a contrast of 1.3 and at 17 minutes of 1.2. I also photographed the same subject in overcast weather and it yielded a contrast of 0.7 in each case, regardless of the development time. The difference between 1.3 and 1.2 could also be a testing anomaly (temperature difference or something?).
What have I learnt from this? No idea. At most: in overcast weather, you always get a low-contrast negative, and in sunny weather, a high-contrast one?
Wilfried
Wolfgg
Hello Wilfried,
It seems there’s still a fundamental misunderstanding here. In sunlight, there can be no contrast in the 1–2 range; it’s much higher than that. Could you please explain what you mean by ‘contrast’ and how you measured it?
Best regards, Wolfgang
wschwetz
Hello Wolfgang,
Perhaps there’s another way of putting it. My Splitgrade measured it that way, meaning the print should have been adjusted by 0–1 stops. For negatives taken in overcast conditions, the gradient would have been around 4 stops.
Wilfried
Wolfgg
Wilfried, am I right in thinking that you’ve only just started developing your own photos and are already using Heiland’s Splitgrade? That would be a bit like a learner driver practising in a car that steers and accelerates itself. To learn how to develop properly, you must initially do without such error-compensating aids and simply enlarge firmly at gradient 2 (gradient-conversion paper without a filter). Your figures do not represent the contrast, but rather the gradient of the paper that the Split Grade module has measured as optimal. The shot taken in sunlight therefore resulted in a soft to extra-soft gradient, meaning: the negative is too hard, over-developed. The shot taken in overcast weather resulted in a hard gradient, i.e. the negative is under-developed.
So: initially, do not use split exposure (referred to as ‘split filtering’ in the English literature), but only *one* exposure without a filter, and then assess the enlargements. And initially, concentrate only on scenes with sunlight. And now the question is: which negative produces the best image?
Regards, Wolfgang
Wolfgg
Mirko: the forum is still on summer time, so the timestamps are an hour ahead.
Best regards, Wolfgang
Edit: Everything’s sorted now.
Wolfgg
Wilfried is probably practising hard now until everything works without the active involvement of the split-grade module. At the start, it’s really important not to be fooled by the automatic functions; otherwise, you can all too easily end up with second-rate negatives, and unless someone with a bit of expertise happens to see your negatives and spots the mistake, you might remain at that level for years. Of course, he didn’t buy the split-grade equipment for nothing; it will prove to be a time- and material-saving aid later on.
Ideally, negatives should always be developed so that you can achieve the exact result with the ‘Special’ gradient (=2). Why? There are only two gradients that deliver a wide tonal range and rich, deep blacks: ‘Special’ and ‘Normal’ (=3). And because it often turns out that an image developed on Special lacks a bit of bite and looks better when made slightly harder, it makes sense to calibrate to Special and then have Normal ready as a harder option.
If you want special effects, the extreme gradients can of course also be useful. But you should only think about that once you have mastered the craft for the standard image.
Regards, Wolfgang
Marcellus
The magazine *Foto Hobby Labor* 5/84 contains a detailed report on Promicrol.
It includes a table that relates subject contrast to exposure and development times.
For low subject contrast, the exposure time should be reduced by two stops and the development time increased by 30%.
For high subject contrast, the exposure time should be increased by one stop and the development time reduced by 30%.
The initial exposure value then refers not to the nominal sensitivity, but to a freely chosen one.
