Pushing ISO up
What does it mean that a developing agent like Diafine pushes the ISO of a film in this case Tri-X ISO 400 to ISO 1600?
Does that mean that I should set my camera settings of speed and aperture base on ISO 1600 instead of ISO 400?
I would appreciate if someone could explain this concept to me, thanks in advance.
Short answer is yes, you can under expose Tri-X by as much as two stops and still get reasonably easy to print negatives from Tri-X. Honestly, I think that the recommended exposure index of 1600 for Tri-X in Diafine is a bit optimistic. It works fairly well when the lighting is flat and there isn't much contrast between the highlight and shadow areas of the scene. It works fairly well if you don't care too much about shadow details and the lighting presents soft to moderate shadows. If shooting conditions present a lot of contrast and hard shadows, you're much better off if you can rate the film at 1000 or 1250. There will be some loss of shadow detail, but if it's the difference between getting the shot or getting nothing, well what the heck.
Originally Posted by jaimeb82
Thanks, that make things more clear, but still don't get something. Today is heavy overcast day here in NYC, so I take my meeter and ISO 400 gives me about 5.6@500/sec. Right after that in same weather light conditions I decide to meeter my exposure base on ISO800 and meeter tells me that at 5.6 I need speed 1000. How could those two different values translate into the same good picture? Am I supposed to chage ISO only when light becomes less available only? But doesn't the Diafine will push my film anyway?
If you underexpose your 400 ISO film by one stop (thus artificially making it a 800) you can close your lens by one extra stop or set the camera to one faster speed (in your example 1000/s instead of 500/s. Your developping agent will have to compensate this (actually you will have to leave your film longer in the bath or, the agent is just more reactive). Your pictures will most probably show bigger grain when "pushing" your ISO this way. Which is fine for portrait or lanscape. I got very good results when shooting lanscapes in the mist.
Another option would be to use fast film (1600 ISO, for instance). But with a 400 and a fst lens you don't have to "push" during processing...
Indeed a short yes, however my best results Diafine and Tri-X (400) were shot at iso 1250.
Diafine can't controll the density in another way and it is in a wide range temperature independent (21-28 degrees C)
So you have to decide in advance what kind of film with the iso speed you're going to use.
Here the Diafine data sheet and my Diafine recommendation table:
Tri-X (400) and Neopan 1600 are doing the best on high iso rate.
Fuji Acros 100 (iso 160) and Rollei ATP1.1 (iso 32, Advanced Technical Pan, not in the list) will give you the finest grain with this easy in use developer.
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The short answer is that they won't. However, by using a developer like Diafine that tends to provide a higher speed with Tri-X, you can at least come close or get decent negs with the higher speed. If you use diafine and shoot at 400, your negs might get a little dense, actually.
Originally Posted by jaimeb82
A film is rated according to the film manufacturer. That's the ISO - meaning the EI (Exposure Index) where you get enough shadow detail according to their tests.
If you give half the exposure by changing from 1/500th s to 1/1,000th s you will under-expose the film. You give it less light.
This means a loss of shadow detail, because shadow detail is almost solely dependent on how you expose the film.
You can compensate for this by developing longer, and you can bring your mid-tones and highlights up to look normal by doing this (exposure AND development determines mid-tones and highlights), but you can never compensate for lost shadow detail.
So, by underexposing to obtain a higher shutter speed, you sacrifice something else - shadow detail.
Instead of underexposing and compensating - try using a wider aperture and get a correct exposure. Or use a film like Ilford Delta 3200, (which is not rated by the manufacturer, but is about ISO 1000).
But if you don't have enough light to expose your film at EI 400, you have no choice. Like Frank says, it's better to get an underexposed frame rather than nothing, if the frame is important to you.
It is better practice to use the film as it was designed to be used. When people do testing of their film, most end up exposing the film at somewhere between EI 200 and 400. It varies from film to film, and some people choose to use an EI of 800, if they don't think that the extra shadow detail is worth much to them. It's a personal choice, and the film will exhibit a different look depending on your choice of exposure and processing. Testing and hard work in processing and eventually printing the negs often. Only after you print your negs often will the whole process come full circle.
"Often moments come looking for us". - Robert Frank
"Make good art!" - Neil Gaiman
"...the heart and mind are the true lens of the camera". - Yousuf Karsh
You need to set the ISO higher and shoot the whole roll that way, otherwise, the images where you metered at 400 may come out too dense when you develop the roll in Diafine. So you decide, when you load the camera, if you are shooting at 800 or 400 or 1200 and shoot the whole roll at that setting, then develop it in Diafine.
Originally Posted by jaimeb82
There are some other things you can do with Diafine to deal with the contrast issues which don't necessarily match the information printed in the materials, and to which Diafine purists will object and tell you that it makes no sense, but they work well. But that is a topic for a different thread...
Ok, so I have to be consistent and decide how much to push up for the whole roll. Let's say I go with RobertV suggestion of pushing tri-x (400) up to ISO 1250 and I don't change that for the whole roll, then? my developing time will increase a little bit to compensate the underexposed film? I didn't take into account the development time, humm I think I must start putting all this into practice, thanks for explaining
It's a two bath developer so you can not control the C.I. with your developing time.
Indeed shoot the whole role Tri-X (400) at iso 1250 and develop 3+3 minutes within the suggested temperature range 21-28 degrees C. You DO NOT have to compensate for the temperature.
Due to the very high pH of bath B there is no acid stop bath recommended. So use a water wash between B and the fixer.
Diafine is a very simple "fool proof" developer. You only have to prevent that no B is comming into A by accident.
Please take notice of my best recommended films with Diafine.
A Quart Diafine (950ml) is ok for about 30 films and this 2-bath developer will be OK for 1 1/2 till 2 years. Particles you can filter out and the colorizing (A) is normal by solving the anti halo layer of the films. Diafine has a long life, easy in handling and it's a cheap developer.