Push / Pull ISO levels?

Joined: 27 Aug 2005 Posts: 389 Location: Sydney, Australia

I shoot a lot of digital black and white but am interested in film (which I have no experience with) so please excuse me if this is a stupid question.

I read keithwms' response to a question as to what film to use:

keithwms wrote:

You might also try delta 400 and even delta 3200. The latter is best when pulled to 1600. For your grainy look you could push delta 400 to 800 or pull delta 3200 to 1600.

What exactly is meant by this? I am guessing that for "pushing", you would expose 400 as if it was really 800, thus underexposing by 1 stop due to too fast a shutter speed - to compensate, as everything would be too dark, you would not allow the development time to be as long and vice versa for pulling?

What is the difference in the grain achieved by pushing 400 to 800 or just using a higher ISO film?

Posted: Wed Sep 06, 2006 8:07 am

Although I'm not that experienced with pushing and pulling films I thought that I would chime in here to fill in what I can.

You're pretty much right about the pushing and pulling definition so I'll leave that be. Although there is one bit where I think you're confused, if you push a film (basically underexposing it) you would then have to develop it for a longer period of time not a shorter period.

The reason why people push/pull film comes down to a few things as far as I can tell:

1) Say you have a 400 iso film in your camera but you need and extra stop for whatever reason, you can push the film to 800/1600 to get the extra stops if you so needed, this is essentially the same as just raising the iso on your digital slr but it would have to be for the whole roll rather than being able to change it for each shot like you can with digital.

2) People seem less objectionable to grain from film and some people purposefully push the film to get a grainier print, this is just for the aesthetics of the shot rather than technical aspects.

3) Pulling film is generally used for the opposite of the above as it generally reduces the appearance of grain in the film.

To answer the question about differences in grain that really comes down to the film itself, if you look around on the net I think you'll find that people generally end up liking the 'look' that they get with certain films. It might also come down to the fact that certain iso films don't exist, I'm not sure I have ever seen a 800 iso film for instance, most people would push or pull a 400 or 1600 iso film to get to 800 iso if they really wanted to.

Posted: Wed Sep 06, 2006 10:18 am

I think Mr. Gringo successfully decoded my quote there ;) what can be confusing is the difference between push/pulling and simply "rating" a film at some ISO different from what's on the box. Rating a film higher or lower than it's standard speed doesn't necessarily imply anything about processing. But push/pulling implies an adjustment in processing.

I'll just add one other stray comment. Regarding grain, some films do quite well when pushed a stop or two, e.g. delta 400. But.... if you shoot 35mm format, grain is much more of an issue: when you enlarge your image, you enlarge the grain with it, of course. Since medium and large format film don't need to be enlarged as much to obtain standard print sizes, you can shoot those at 3200 or 6400 and still not be overwhelmed by grain. That's a good thing because most medium format lenses are really slow compared to what you get in 35mm- typically f/3.5 or slower.

:) keithwms

Posted: Wed Sep 06, 2006 10:41 am

One more thing to add, as this if often overlooked:

Push-processing will not only increase grain, but also contrast. This is more obvious with slide film, but also present in negative material

Pull-processing, on the other hand, will not decrease contrast...

Pushing Velvia 50 to 100 ISO will stilll show low grain, but even more contrast, quite suitable for very drab lighting.

Pushing bw film is easy, just raise the development temperature slightly. Most books emphasize to prolong development time, but this mostly increases contrast. To really gain ISO steps, a higher temperature is the road to go.

I one pushed Tri-X to 3200 ISo for evaluation and added a final step of a bath in oxygenperoxide fumes, which is supposed to reduce grain. But even then, the single grain hardly fitted in the 35 mm frame...

regards
René

Joined: 27 Aug 2005 Posts: 389 Location: Sydney, Australia

Thanks guys - the one thing I am slightly confused about as El Gringo pointed out - development time. With numbers just as examples, please let me know which step is incorrect.

1. Insert 400 rated film and shoot as if it was 800
2. This will result in less than ideal amount of light hitting the film
3. As such the negative will be lighter than usual as the light is what darkens the crystals
4. When enlarging, this will allow more light to pass through the negative and onto the paper
5. The light hitting the paper is what darkens it (similar to film)
6. As such the paper will become darker than with proper exposure (development time kept equal) because of extra light
7. Hence, to counteract this you would let less light through by decreasing time

Where is my mistake?

Posted: Thu Sep 07, 2006 5:44 am

spaz wrote:

Thanks guys - the one thing I am slightly confused about as El Gringo pointed out - development time. With numbers just as examples, please let me know which step is incorrect.

1. Insert 400 rated film and shoot as if it was 800
2. This will result in less than ideal amount of light hitting the film
3. As such the negative will be lighter than usual as the light is what darkens the crystals
4. When enlarging, this will allow more light to pass through the negative and onto the paper
5. The light hitting the paper is what darkens it (similar to film)
6. As such the paper will become darker than with proper exposure (development time kept equal) because of extra light
7. Hence, to counteract this you would let less light through by decreasing time

Where is my mistake?

Hi spaz
your points 1 to 7 are correct. But you omitted one important fact: Pushing means, to increase the ISO rating of the film + developing it accordingly. Thus the density of an 400 ISO film exposed and push-processed to 800 ISO would be the same, as that of an 400 ISO film exposed at 400 ISO and developed nominally. (These are differnet thing: exposure time (the time light interacts with the film or printing paper and development time, which is the time for the photo chemicals to interact with the film or print emulsion.)

Also printing an underexposed film (because it wasn't push-processed) would reveal, that you lost the shadow details (blank white on the negative) and in total would compress the tonal and dynamic range, leading to a flat print.

So decreasing exposure time during the printing stage is only a last ressort and poor substitute (because of the quality loss) to push-processing the film.

regards
René

Joined: 27 Aug 2005 Posts: 389 Location: Sydney, Australia

Thanks René - glad I'm not completely off the track. Hopefully soon I'll get an opportunity to work in a darkroom (when the money starts rolling again) to get a better grasp.

Thanks to everyone else as well, it's good to see so many correlations between the way BW film is developed and the way I do digital conversions.

Joined: 05 Oct 2004 Posts: 565 Location: Toronto

Scala 200 is a black and white slide film that works very well when pushed. There's virtually no grain, however it becomes very contrasty. It's a lot of fun to experiment with.

Posted: Thu Sep 07, 2006 6:47 pm

Nate wrote:

Scala 200 is a black and white slide film that works very well when pushed. There's virtually no grain, however it becomes very contrasty. It's a lot of fun to experiment with.

Yes, nice stuff. The only thing is, I have to ship it to California to have it developed ;)

R3 is also very pushable, right up to 6400, and can be processed in a more conventional way in a lab near you. And it's an affordable print film. I think there is a way to do reversal processing for slides as well.

Joined: 09 Sep 2006 Posts: 114 Location: Boston, MA

this info may have been posted above, but i thought id chime in with my experience.

When shooting any type of negative film be it B/W or color always shoot 1 stop slower execpt for iso 50 and 125. Film manufacturers have specific tests to determine film speed which do not adapt to real world shooting. these tests are done in a lab and are strictly controlled. I learned this in Photo school from professionals and people that work for ilford and kodak. So you shoot ISO 400 at 200 and 1600 at 800 ect ect. B/W has a significantly larger lattitude than color neg so your pushing and pulling is done more with your processing time than with your exposure.

If I were to expose ilford HP5 (ISO 400) at ISO 200 and develope in D76 for the standard time of 12 mins at 20 degrees C I would yeild a density on the film which was very close to the contrast range in my scene. its also worth noting that b/W film has a 5-7 stop dynamic range so if you know the zone system it will greatly aid your pushing an pulling. the scale is from 1-10, 1 being pure black with no detail and 10 being pure white with no detail. 5 is middle grey. in B/W always always always expose for the shadows. this will gain you detail in your shadows while still leaving you detail in the highlights which can be burned in in the darkroom. Im getting off track but im going to keep going. If I am shooting a scene and my exposure for the shadows is say f8 @ 15sec and my exposure for the highlights is f8@ 2000sec than I know that my dynamic range or contrast is 8 stops and if I expose for the mid tones which would fall somewhere around at f8 @ 125 sec i will lose detail in my shadows and put my HL values somewhere around lightgrey. so expose for your shadows which would be f8 @ 15 sec. this will place my shadows in the grey area and still leave me detail in my HL.
that said I will now process my film for the highlights. processing for 1 to 2 mins more than the standard time to build density in the shadows and the highlights. its important to note that in processing the highlights are effected very little, it is the shadows that can be lost to pure black. So always expose for the shadows and process for the highlights. I use ilford FP4 (125) and process 8 mins for a very high contrast shot and 12 mins for a low contrast shot. 10 for a scene with contrast within the range of my film. In the darkroom i use contrast filters to build my shadows up without lossing the detail and burning to bring my highlights in.

On to pushing and pulling.
So if you use the above method and you shoot say delta 800 @ 1600 you still need to expose for the shadows and process for the highlights...using the processing times for delta 1600 and adding time to your processing if needed. you will yeild and exposure that is correct and less grainy although less contrasty due to the reduced processing time. remember that the film is overated so iso 800 is actually 400 so shooting at 1600 is 2 stops faster. take this into careful concideration.

pulling
pulling of ISO 3200 to say 800 will yeild you a very grainy image that is high in contrast and may be lacking mid tone values...everything is either in shadow or HL. you will have to test and find the correct shadow exposure and processing time to achieve the density you like. It is a very interesting process and can yield very impressive results..just know that it takes testing and patients to get right.

Stay away form kodak HC110 if you are going to pull process...it is a non silver developer and yeilds very high contrast..plus the times are too short and it is easy to "burn" the film. I use D76 which has never given me poor results.

Hope this help.. i know it is probably confusing. i am not a literary genius.

Joined: 09 Sep 2006 Posts: 114 Location: Boston, MA

To correct a few errors in posts above..

Increasing the temp of the developer and increasing developing time are one in the same. An increase in temp needs a reduction in time. All this is doing is allowing the developer to more aggressively dissolve the sliver halide salts on the film. if I normally use 12 mins at 20 degrees c (68 F) and I heat the developer to say 72 F i need to reduce my time to achieve the same processing. raising the temp also runs you the risk of creating reticulation in your film and possibly burning your film ( too much development too fast) if you raise the temp of your developer than you must raise them temp of your fixer...changing the temp of the film before the image is fixed will result in reticulation.

Developer works by disolving the sliver halide salts on the film that have not been exposed to light. which means that highlight values, which have the greatest exposure are not acted upon as much as shadow values which have the lowest exposure. when you look at your negatives which part is the lightest or clear? the shadows. So by developing longer you are acting mostly on the shadows and very little on the HL. You can infact expose a grey object and a HL value and process for such a time that the grey falls into black shadow without losing all your HL information.

Yes pulling results in more contrast unless you take into account your development times.

pushing does result in less contrast due to a significant reduction in development time unless you compensate with more time.

your goal should be to produce a medium density negative...with no clear or pure black film....contrast control is done in the darkroom. it is easier to work with a neg full of grey values and build contrast with filters and time and pull back the HL with burning tham to work with a very thin or very dense neg. plus a good medium density negative can be printed most anyway you want. a thin neg and a dense neg..or even what some call a perfect neg has very limited printing options.

The exceptions to all this are if you are shooting in very controlled lighting in which you can build your film density using lighting control, GOBOs and multiple exposures across the same piece of film. This is what studio photographers due for advertising with a chromes and a 4x5. its very controlled and yields a negative when processed correctly that will print without filters or burning and dodging.

Joined: 30 Nov 2006 Posts: 73 Location: Sheffield, England

So am I correct in saying that if an ISO 400 film is pushed to 800, you would develop it as if it were a 800 film?

Posted: Wed Jan 03, 2007 5:48 pm

cjdales wrote:

So am I correct in saying that if an ISO 400 film is pushed to 800, you would develop it as if it were a 800 film?

This can be so - or not... Film rated at ISO 800 might sport the same development parameters as film rated at ISO 400. But ISO 400 film exposed at ISO 800 should be longer developed (or at higher temp.). A longer dev. time than the standard time mentioned in the developer's papers will always result in increased contrast (except: se below).

But this is highly dependent on the developer/film combination you use. For example a two-step developer like Emofin would not necessarily require a prolonged dev. time, because it "optimizes" contrast anyway during the dev. process.

regards
René

Posted: Wed Jan 03, 2007 6:40 pm

throughthelens1125 wrote:

To correct a few errors in posts above..

Increasing the temp of the developer and increasing developing time are one in the same. An increase in temp needs a reduction in time. All this is doing is allowing the developer to more aggressively dissolve the sliver halide salts on the film.

The developer does not dissolve anything. That would be the fixer, which removes the undeveloped silver halides. The developer reduces the silver halides to metallic silver.

Increasing dev. time should not be completely equivalent to raising the dev. temperature. Dev. time increase also leads to more fogging, than dev. temperature increase. Both ways lead to increased contrast and grain. But this is fairly dependend on the actual parameters, including the film of choice. So I would give in and accept, that dev. time increase and temperature increase could be equalled within reasonable limits.

From a certain level of push-processing on, graininess and contrast increase can be quite unacceptable, though there are ways to decrease graininess to some extend... But then it gets complicated and unhealthy due to the chemicals required.

throughthelens1125 wrote:

if I normally use 12 mins at 20 degrees c (68 F) and I heat the developer to say 72 F i need to reduce my time to achieve the same processing. raising the temp also runs you the risk of creating reticulation in your film and possibly burning your film ( too much development too fast) if you raise the temp of your developer than you must raise them temp of your fixer...changing the temp of the film before the image is fixed will result in reticulation.

fortunately modern emulsions are quite robust and less prone to the effects you describe. If one keeps the temperature o the baths within reasonable limits, the danger of reticulation is minmal, not to say nil. I have only seen this reticulation on one film during more than 25 years lab work - and that was an old fashioned Tri-X, when the fixer and rinse were very much colder than the developer.

throughthelens1125 wrote:

Developer works by disolving the sliver halide salts on the film that have not been exposed to light.

as I wrote above: The developer does not dissolve anything. The contrary is true, it works only on the exposed silver halides and reduces those to metallic silver. This is exactly the reason, why a fixing bath is necessary at all, because only the fixer finally removes the unexposed silver halides.

throughthelens1125 wrote:

which means that highlight values, which have the greatest exposure are not acted upon as much as shadow values which have the lowest exposure. when you look at your negatives which part is the lightest or clear? the shadows. So by developing longer you are acting mostly on the shadows and very little on the HL. You can infact expose a grey object and a HL value and process for such a time that the grey falls into black shadow without losing all your HL information.

Due to the way developer works, it will develop exposed areas (lights) more intense, than unexposed (shadows) areas. In areas, which did not receive enough light to exite the silver halide clusters at all (blacks without further detail) = completely blank areas on the negative), the developer will not do anything, except increase random noise (= raising the fog level). This would contradict the quoted paragraph completely.

throughthelens1125 wrote:

Yes pulling results in more contrast unless you take into account your development times.

Pulling usually "takes into account" development times, as it is usually based on reducing the dev. time, thus decreasing contrast, not increasing it.

throughthelens1125 wrote:

pushing does result in less contrast due to a significant reduction in development time unless you compensate with more time.

Pushing does not need to be "compensated" by increasing dev. time - it is actually achieved (as the standard procedure with all its short comings) through increasing the dev. time. Pushing automatically leads to increased contrast and grain too, except when you use step development or other special processes.

throughthelens1125 wrote:

your goal should be to produce a medium density negative...with no clear or pure black film....contrast control is done in the darkroom. it is easier to work with a neg full of grey values and build contrast with filters and time and pull back the HL with burning tham to work with a very thin or very dense neg. plus a good medium density negative can be printed most anyway you want. a thin neg and a dense neg..or even what some call a perfect neg has very limited printing options.

Oh yes, I completely agree. There are some people who hail thin negs, because our grandfathers needed this to keep the grain of old emulsions within limits. But today, were grain is not a problem, thi would be nonsense, because it brings loads of problems and loss of quality during the printing stage - as you wrote.

throughthelens1125 wrote:

The exceptions to all this are if you are shooting in very controlled lighting in which you can build your film density using lighting control, GOBOs and multiple exposures across the same piece of film. This is what studio photographers due for advertising with a chromes and a 4x5. its very controlled and yields a negative when processed correctly that will print without filters or burning and dodging.

Indeed every corecctly exposed slide should be like that, because it has a much smaller exposure latitude than neg. film and usually is the final result. Well, should have written this in past tense, as today in commercial photography digital is the usual means...

regards
René

Joined: 30 Nov 2006 Posts: 73 Location: Sheffield, England

So how do you know how much more time to give the film when it is pushed?