To push one stop or fix in DI

Brian Pritchard · February 4, 2010

Besides the decrease in grain perception (esp. in S16), this is another good reason to rate stocks 2/3s slower... Most underexposures are between 2/3 and 1 stop under so, if you forget to compensate for an 85 for example, you are still in 'normal' range.

I have to agree with Mr. Pritchard and anyone who has ever pushed has heard the lab express to them that they will not yield a full 1 stop on a 1 stop push. I also think there is a bit of semantics going on in that pushing does not increase speed (on the low end) because as David M. stated.. it occurs after the fact and we can not bring to life something that is not there in the first place. At the same time, pushing can bring to life things that are under between the mid and lows.

On the Fotokem Test I saw no increase in Contrast or Grain in a 1 stop push (which is really 2/3s) in either 35mm or S16mm.

I think we have nearly exhausted this subject.

However I do not accept that because you have already exposed the film push processing will not yield an increase in speed. As the Kodak website explains if you push by 1 stop you get an actual increase in speed of 1/3 stop. The film records all the information that is available. Some grains will not receive sufficient exposure to be able to be developed at a particular film speed, if you then push process these grains will be developed and you will gain information.

Film does not just stop recording at a particular light level, it is a case of whether the grain has received sufficient exposure so it can be developed. Extra development will develop grains that would not be developed with less development.

What we are talking about is the difference between push processing and intensifying. If you intensify a B/W negative that has already been processed you cannot bring up any more information, you just make the negative heavier. If you give a B/W negative extra development you will bring up extra information. This is why manufacturers give different exposure ratings for different developers for B/W still stocks. Colour negative is no different. Working on a processed colour negative digitally is the equivalent of intensifying it and cannot produce additional information that is not already there. Push processing can.

Brian

David Rakoczy · February 4, 2010

However I do not accept that because you have already exposed the film push processing will not yield an increase in speed. -Brian

... not if you have no info in the blacks because you did not have sufficient speed to register anything to begin with.

I believe people are talking about different parts of the curve in this discussion.

Don't make me regret agreeing with you. ^_^

David Rakoczy · February 4, 2010

Working on a processed colour negative digitally is the equivalent of intensifying it and cannot produce additional information that is not already there. Push processing can.-Brian

This is factually incorrect... Pushing can (not) bring out information where no information exists... it can not just 'make it up'.

This topic may be exhausted for you, however, the more you write the more there is to discuss ;)

David Rakoczy · February 4, 2010

Film does not just stop recording at a particular light level,-Brian

Case in point :rolleyes:

For all practical purposes, Film sure as heck (can and does) reach a point where it does not have sufficient light to garner (anything)... unless you want to wade into the theoretical (and certainly not practical) world of pushing 5, 10, 50 or more stops... where do you stop?

That is why I said I believe people are talking about differring points of the curve.

Brian Pritchard · February 4, 2010

This is factually incorrect... Pushing can (not) bring out information where no information exists... it can not just 'make it up'.

This topic may be exhausted for you, however, the more you write the more there is to discuss ;)

The whole point I have been trying to make is that the information is there. The more you develop (with-in reason) the more the information you will pull out.

Brian

K Borowski · February 5, 2010

Right, I can agree, Brian, that there is SOME speed gain, but the bulk of the effect is that there is a perceived speed increase through built up contrast than an actual speed gain.

Even if you gain a third of a stop's speed with a one stop push, I would say that you only gain detail in the LINEAR (not highight, not shadow) portion of the curve.

You may gain a third of a stop of mid-tone detail but all shadow detail is completely lost. You have to keep this in mind when pushing that if you are underexposed a stop in the shadows, that even with a one stop push, you are going to essentially lose that information due to two stops' underexposure.

And it is a case of diminishing returns. You'll gain *something* in a one stop push, but almost nothing (except more contrast and base fog) if you push more than one F/stop.

Of course it all depends on the stock. I remember that B&W stocks were more compatible with pushing, and there are different speed layers embedded in each different stock, so it is not as if a 500T stock is only sensitive to that speed. There are slower and faster grains as well in there, so there is a range of exposure information built in, unlike old stocks where there was very little latitude.

Dominic Case · February 7, 2010

If you push process a 50 ASA film 1 stop, then it is, as far as exposure concerned, equivalent to using a 100 ASA film,

Well, I thought I'd missed this list for a while - so I log in, and find this going on! How can I stay out???

So no, Brian, I won't support this argument. I might agree that if you push 50EI film one stop then as far as mid-range density is concerned, it's equivalent to using 100EI film. But the effect is very much less at lower light levels, so it's not the exact equivalent (even just in terems of exposure) of a faster stock.

The Kodak explanation you cited puts it about as accurately as one could wish for.

I'm not sure that I am 100% with David either, though I agree that in simple terms, no amount of developing can reveal an image detail that hasn't been captured in exposure.

Elsewhere you (Brian) said:

Film does not just stop recording at a particular light level, it is a case of whether the grain has received sufficient exposure so it can be developed.

Exactly so. And there is a wide range of grain sizes in any emulsion so that even in very low light levels there will be some grains that are big enough to capture the required number of photons to make them developable.

This "sufficient exposure" is really the crux of this argument. Is it a fixed amount,or does it vary with developing time.

What a developing agent does, is react with ALL silver halide grains. It happens to react with exposed ones quite quickly, and unexposed ones very slowly. Longer development time (forcing) means that exposed silver grains are more developed, so forming more developer by-products that in turn couple with the colourless couplers to form more (bigger, more intense) dye clouds. It also means that more "unexposed" grains will be developed, leading to some dye clouds in the unexposed areas and a higher d-min or fog level.

Meanwhile, though, the question in hand is whether more development will also dig out those grains that got sub-threshhold exposure for normal development, and give them a life that will distinguish them from still less-exposed ones.

In other words, does the threshhold of exposure (enough to produce the first hint of density above d-min) vary with development. I think the answer is yes, but not as much as you'd think. That is really what the Kodak quote is saying.

However, is the original question about whether the cinematographer with the Bolex (remember him, a few post ago??) should force process or look for correction in DI.

If he was counting on seeing deep deep shadow detail, then he should push process. If he was simply wanting to avoid an "under-exposed look" with flattish shadows and poor contrast then he will be able to recover from that perfectly in the DI grade. And incidentally, he will avoid the increased graininess that the push process would result in.

Brian Pritchard · February 7, 2010

Dominic, I thought you had gone walk-about into the outback; I must admit I was beginning to feel overwhelmed. Of course I agree with what you say, a very clear and succinct reply. Perhaps I do know a little about push processing after all!

Brian