B/W Film Testing Question

[LFLarry]

Hi, I recently found a working densitometer at a yard sale and I couldn't resist getting it.

I am familiar with the basics of testing film (EI established at Zone 1/.10 density units above film base + fog) and Normal development being established at Zone VIII with a density of 1.25 to 1.3 for my cold light head enlarger.

I am going to give HP5 a try for the first time and I thought this would be a good time to put the new densitometer to use.

In "theory" HP5 could be rated anywhere between EI 250 up to 3200. I was thinking there have been many times when I wish I would have had a couple extra stops because of wind, etc.

My question: If I rate my HP5 at EI 800, how would this impact my density measurements for development at Zone VIII? I know that I will have to develop longer when rating at EI 800, so should I try and attain the same 1.25 to 1.3 density but expect an increase in general contrast?

Thanks in advance.

Larry

[koraks]

Larry, with push processing, if you aim for 1.25-1.3 at zone VII your zones VIII and higher will likely come out a little higher than they would at a lower EI and your shadows will come out lower, with zones I and II likely not being above b+f. So in short: higher contrast. In addition, due to the toe of the film, the h/d curve will likely be less linear than if you expose at an EI closer to (or below) box speed.

[Peter De Smidt]

Remember that those are net density figures, i.e. minus fog. Read the clear part of a developed negative, and subtract that value your readings. Regarding Zone 1 being .10 above film base plus fog, I'd change that to Zone 1 being at least 0.10 above film base plus fog for traditional silver printing, and where there are important dark areas in the scene. When you push film, you're effective minimizing shadow detail from zone III and down and making up for it, kinda, by increasing tonal separation in the rest of the range. That can work really well with the right scene. So, I would do Fred Picker's Zone VI Workshop style testing, using 1/3 stops instead of 1/2 increments. Nail down your normal exposure and development. You can then compare what happens when you up the EI, as well as determine what to do about it.

[LFLarry]

Hi, thanks for your comment. I think I am clear on my understanding of push processing, meaning that I am over developing the film to try and make up for underexposure because I rated the film above the true EI rating of the film.

I also expected to see a different film characteristic curve when pushing too, as you indicated in your comments.

I don't know this yet, but I suspect the film base + fog may increase when push processing too. I will confirm once I start the testing process.

From a film testing theory perspective, do I still want to try and attain .10 density units above above the film base + fog for Zone 1 when pushing to EI 800 or does the theory change on this? So, for example, if my true EI for HP5 was EI 200, then pushing to EI 800 would be + 2 stops. Then the same question applies to my Zone VIII reading. Do I still strive for a 1.25 to 1.3 density above film base + fog or is that even possible when pushing like this? I ask all of this because I want to know how to properly ensure that I am developing for N when pushing the film.

I am trying to understand the theory so that when I do my testing and start taking the readings, I can make sense of what I am seeing with my density readings.

I am using a 21 step transmission wedge from Stouffers for my testing, so I plan to make a curve for the film/dev combo when using at the proper EI and N development and also a new curve for the push processing and N development. I expect the curve to much less linear, but it will be fun to see what happens in my environment.

Thanks

Larry


Larry, with push processing, if you aim for 1.25-1.3 at zone VII your zones VIII and higher will likely come out a little higher than they would at a lower EI and your shadows will come out lower, with zones I and II likely not being above b+f. So in short: higher contrast. In addition, due to the toe of the film, the h/d curve will likely be less linear than if you expose at an EI closer to (or below) box speed.

[Bruce Watson]

In "theory" HP5 could be rated anywhere between EI 250 up to 3200. I was thinking there have been many times when I wish I would have had a couple extra stops because of wind, etc.

Yeah, but it doesn't really work like that. A "one stop push" is actually a "one stop under exposure". And if you don't give the shadows enough exposure for the film to form a latent image... there's nothing on the film for the developer to develop. So you loose (in this case) a stop of shadow detail. Clear film is clear film, and all that.

The reason you develop longer after a "push" is to compensate for loosing that shadow detail. If you don't, your metered six stop wide image becomes a five stop wide image (because you lost a stop of your shadows due to the underexposure). So you increase development and end up with more stops of tonality (but nothing you do will bring back shadow detail that the film didn't record). IOW, all the extra development is doing is adding density at the highlight end of the range. If you go too far the image on film becomes difficult to print/scan because the higher the density in the highlights, the more Callier Effect you get from it, due to the extra metallic silver making up that higher density. And that extra metallic silver results in more and bigger grain clumps, seen as grainier highlights in the final print.

I'm just sayin' that pushing is a myth. But it can be a useful myth if you don't care about loosing that shadow detail, or adding some graininess to the highlights.

[LFLarry]

Hi Bruce, I am tracking with your thoughts. Makes more sense to me now...

I will start my testing next week and see how all this goes. It will be fun to test all this and then see how it really applies for real image making.

Thanks for your help.

Larry



Yeah, but it doesn't really work like that. A "one stop push" is actually a "one stop under exposure". And if you don't give the shadows enough exposure for the film to form a latent image... there's nothing on the film for the developer to develop. So you loose (in this case) a stop of shadow detail. Clear film is clear film, and all that.

The reason you develop longer after a "push" is to compensate for loosing that shadow detail. If you don't, your metered six stop wide image becomes a five stop wide image (because you lost a stop of your shadows due to the underexposure). So you increase development and end up with more stops of tonality (but nothing you do will bring back shadow detail that the film didn't record). IOW, all the extra development is doing is adding density at the highlight end of the range. If you go too far the image on film becomes difficult to print/scan because the higher the density in the highlights, the more Callier Effect you get from it, due to the extra metallic silver making up that higher density. And that extra metallic silver results in more and bigger grain clumps, seen as grainier highlights in the final print.

I'm just sayin' that pushing is a myth. But it can be a useful myth if you don't care about loosing that shadow detail, or adding some graininess to the highlights.

[neil poulsen]

Remember that those are net density figures, i.e. minus fog. Read the clear part of a developed negative, and subtract that value your readings. Regarding Zone 1 being .10 above film base plus fog, I'd change that to Zone 1 being at least 0.10 above film base plus fog for traditional silver printing, and where there are important dark areas in the scene. When you push film, you're effective minimizing shadow detail from zone III and down and making up for it, kinda, by increasing tonal separation in the rest of the range. That can work really well with the right scene. So, I would do Fred Picker's Zone VI Workshop style testing, using 1/3 stops instead of 1/2 increments. Nail down your normal exposure and development. You can then compare what happens when you up the EI, as well as determine what to do about it.

Net densities are used to determine film speed, i.e. 0.1 density units above film base plus fog. Characteristic curves are based on actual densities without subtracting the density of a clear portion of the negative. Characteristic curves are used to predict print values, and the entire negative contributes towards those values.

Like many people who test film speeds, my speed for HP5 (for example) tends to come out at about half of that recommended by the manufacturer.

Push/pull is too often related to "changing" the speed of the film, which can imply a change in the film speed, so I avoid these terms. I prefer thinking of this as increasing and decreasing development time so as to align the negative contrast with the scene being photographed, while keeping film speed the same.

A good reference for all of this is the New Zone System Manual (White, Zakia, Lorenz.) 1976. I prefer this to either Picker or Adams.

[Doremus Scudder]

There's a real difference between using development time adjustments to tailor a negative's contrast for lower/higher than normal contrast scenes and so-called "pushing."

For the former, a full and correct exposure is given to render the shadow detail as desired and the development time is adjusted to get the highlights to end up with a suitable density for easy printing. Zone System users like to refer to this as expansion or contraction. Note that the exposure is based on a pre-determined optimal film speed or E.I. and that the film is not "rated" faster than that.

With pushing, we intentionally underexpose, and accept the fact that shadow detail will be irretrievably lost, in order to get any kind of shot in difficult lighting situations. We "rate" the film at a higher E.I. to make an automatic underexposure quickly when using in-camera meters. This gives a negative, that when developed "normally" would have no shadow detail and highlights that end up somewhere in the mid-tone range. So, to make the negative more printable, we extend development to stretch out what tonalities were recorded on the neg over the usable printing range (i.e., so that the most-dense values print white in the print, not gray).

If you're using a densitometer to find film speed á la Zone System, then you're not pushing. If you underexpose your film by rating it higher than it really is, then you can use your densitometer to find the right development time to put your high values where you want them (Zone VIII). But film speed is film speed; it changes only marginally with different developers and times.

Best,

Doremus

[ic-racer]

If I rate my HP5 at EI 800...

In most "Zone Systems" out there, you can't just arbitrarily pick an EI. If you increase development of film to match a low contrast scene, your EI may go up (as in the "Beyond Zone System") but in terms of actual film speed under ISO conditions, the ISO speed does not change (because by increasing development you no longer satisfy ISO criteria for measurement).

[Bill Burk]

If you intend to use 800, you might roughly double your Zone VIII density (so if normally 1.2, aim for 2.4)... And you're sure not going to be using that Zone VIII.

If you pretend it's 1600 you will be getting nothing in your shadows.

The toe just doesn't move that much with changes in development.

If you draw yourself some graphs you'll see what's going on. There's nothing to be gained from pushing film beyond about a stop.

Here's an example (TMAX 100) where I can get the speed up to 200 easily enough, but I don't know how anyone could even imagine getting 400 from this film:


http://beefalobill.com/images/tmxfamily.jpg