How Does Developer Affect Film Speed?

[marcmarc]

Hi Everyone,

I've been doing my own b&w film developing and printing for four years now. One thing I never could completely understand is when a developer is described as "speed increasing " or that it will work at the expense of film speed. Now then here in a nutshell is what I have learned either by experience or in the classroom or by reading forums such as apug:

1) Most film iso's are arrived at by the manufacturer under controlled tests and are often more optimistic (i.e. higher) then their ideal iso in the real world. This is why it seems many photographers rate their film at half the iso or more. I often do as well. One of my teachers used to say "No amount of darkroom work will put detail in a print if the detail isn't on the negative". So goes the old rule of thumb - expose for the shadows, develop for the highlights.

2) During development, the thin, shadow areas get developed first. After about half way through the development time, these areas are developed as much as they can be. Any detail not present in the shadows simply means not enough exposure was given to the film. Meanwhile, the highlights keep building up and will continue to do until the developer is dumped and stop bath introduced.


So here's where I get confused. Why would a particular developer be said to give a film it's box speed while another is said to increase speed and yet another will rob a film of speed. I thought film speed was strictly related to exposure. It seems to me that this must refer to highlight detail since the longer development is carried out, the denser the highlights get until detail is lost. I have a copy of The Darkroom Cookbook and if I recall correctly, high acutance developers decrease speed. Rodinal is my most used developer (followed in order by HC-110 and Clayton F-76) and back when I was a beginner I would always expose my film at the box speeds. Sure I got some muddy shadow areas but that improved when I started over exposing a stop. Am I correct in thinking that another developer will yield similar detail at box speed then Rodinal?

I really appreciate any info anyone can give. Please keep in mind that I'm not too familiar with the more technical aspects of film and development. I've heard of shoulders and curves to describe film and development, but really don't know what they mean nor do I use the Zone System.

Thanks,

Marc

 

[Denis R]

film has different push properties, underexposure latitude

kentmere 400 use at 400 kodak t-max 400 can be used at 400 and 800 without increasing developing time, but when pushed to 1600 or 3200 the time increases

best way to understand is to PRINT the data sheets and READ them COMPARE
developer has different properties for grain, contrast, shadow detail, push

 

[David A. Goldfarb]

Generally, film speed is defined by shadow detail. The usual "speed point" on the film curve is determined by the exposure at which a Zone I density of Dlog 0.1 over the density of the film base plus fog (a somewhat arbitrary value, which you may decide is inadequate for your objectives) appears on the film. Extending and decreasing development time will have a much greater effect on highlight values than shadow values, so the idea of "pushing" by extending development times does not really amount to changing the actual film speed significantly (even if this is the advice given on manufacturers' data sheets), but you can change the film speed by choice of developer and by various other methods like pre-flashing (which arguably doesn't change film speed, but seems to), exposure of the film to ammonium vapors, minimal agitation techniques, and such.

What a speed developer like Acufine or Microphen does is like developing to lower contrast, so you can extend development time to increase shadow detail without losing control of the highlight detail, as you might with a conventional developer like D-76. These developers can usually get an honest one to two stop increase in film speed with normal contrast.

Read Ansel Adams' book, _The Negative_. It explains all those things you say you don't quite understand. Even if you decide not to use the Zone System, it's a good way of learning how film works.

 

[Jeff Searust]

get a copy of the Film Developer Cookbook. Much better info than can be had Anywhere else.
http://www.elsevier.com/wps/find/bookdescription.cws_home/676062/description#description

 

[Ian Grant]

Back to the OP's point about High Acutance developers they usually give increased film speed, not a decrease.

In real terms Rodinal gives much the same film speed as D76/ID-11 or Xtol to get similar tonality.

Ian

 

[ic-racer]

Using, say 0.1 log d as the speed point, the biggest difference I have seen is about 1/3 of a stop between say 100:1 Rodinal and T-max developer.

 

[Ian Grant]

You don't say what the film is, but that's about right for Tmax films where Tmax dev was brought out to bring out better effective film speed.

Ian

 

[ic-racer]

You don't say what the film is, but that's about right for Tmax films where Tmax dev was brought out to bring out better effective film speed.

Ian

That was T-max film. I searched through a bunch of test files and, to make an example, picked datasets for two of my tests for T-max 400 that had similar gamma and looked the farthest apart.

I have not tested all combinations, but my impression is that if your baseline is T-max developer, then you are probably unlikely to get an additional 1/3 of a stop of speed with any Acufine, Rollei High Speed, or Microphen type of developer.

 

[MattKing]

The ISO specification for film's light sensitivity isn't optimistic - it is just the result of measuring that sensitivity under a particular set of conditions. If you change those conditions (e.g. change metering, equipment, or the developer) you may get a different number, but it won't be the ISO for the film, it will be an EI number particular to those changed conditions.

The ISO specified conditions aren't necessarily unreasonable - I expect they were chosen because they are both close to average real world conditions, and easily repeatable.

Matt

 

[Alan Johnson]

Here's Richard Knoppow from rec.photo.darkroom on the subject:
http://groups.google.com/group/rec.photo.darkroom/msg/a6b907c010446708

 

[Ian Grant]

Here's Richard Knoppow from rec.photo.darkroom on the subject:
http://groups.google.com/group/rec.photo.darkroom/msg/a6b907c010446708

There's a major flaw, or rather assumption in Knoppow's writing here.

He's taking ISO to mean the ASA/BS standard method of testing, but in fact the ISO stanard also includes DIN the German Standard.

The dual system is still there in the 100/21° etc.

So a fim could be tested by one or the other and a conversion made. Ilford, Fuji & Kodak used the ASA/BS method of determining film speed while Agfa used the DIN system.

One major advantage of the DIN standard is the test is more practical, and the speed arrived at gives a fuller tonal range for normal use.

In many ways the ISO/ASA testing method is flawed, as Ilford now say:

It should be noted that the exposure index (EI) range recommended for 100 DELTA Professional is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard

This is more likethe DIN testing system, Colour film speeds are determined in a similar way.

In practical terms my own Zone system tests of Tmax 100 and APX100 and Rodinal gave an Tmax 100 an EI of 50 and APX100 EI 100 - box speed.

But the major difference was that Agfa's box speed was based on the DIN tests, Tmax100 by the ASA method. In the datasheet for Tmax 100 it said for full tonality rate at 50 EI.

Ian

 

[ntenny]

From the perspective of the OP's question, the answer I'm taking away from these explanations is that it's *not* in fact true that the shadows routinely develop to completion.

If they did, I guess the original analysis would be right, wouldn't it?---a "true increase" in film speed, as measured by shadow detail, would be impossible, because the shadow detail would be fully revealed by the development to completion that takes place under normal conditions. From what others have said, speed-increasing developers really do find and develop more activated grains in the shadow regions.

Have I got it right so far?

If so...then why doesn't a longer development time do exactly the same thing? Why *isn't* it possible for extended development in a different developer to pull out those same activated grains?

-NT

 

[dancqu]

Maximum Speed Without Undo Density

If they did, I guess the original analysis would be right,
wouldn't it?---a "true increase" in film speed, as measured
by shadow detail, would be impossible, because the shadow
detail would be fully revealed by the development to
completion ... From what others have said, speed
increasing developers really do find and develop
more activated grains in the shadow regions.

Have I got it right so far?

If so...then why doesn't a longer development time do
exactly the same thing? Why *isn't* it possible for
extended development in a different developer to
pull out those same activated grains? -NT

Last first, longer development in and of itself
may result in too high a contrast. Also Fb+fog
may exceed tolerable levels. Overall I believe
any developer which will maximize film speed
works in a compensating manor. That is it is
slow via one means or another
in building density.

Two bath and very dilute developers are two
means by which thin areas of the emulsion
are favored for development; developer
becomes depleted in those areas
which are most exposed.

It is my believe that almost any developer
used as I've mentioned can act as a speed
enhancer. I've been using D-23 at a 1:7
dilution; full+ speed and good density
control. Dan

 

[c6h6o3]

Push development is a myth. 1/3 a stop or so is useless. Just use a faster film.

 

[Ian Grant]

Push development is a myth. 1/3 a stop or so is useless. Just use a faster film.

Try telling that to people who regularly push process Tri-X, HP-5, Delta and Tmax 400 and the faster films.

If you think it's a myth fine, they'll just keep shooting when you've retired because the lights too poor

Ian

 

[tkamiya]

I was wondering about something similar.

I use Tmax-400 film and XTOL developer. According to Kodak's literature for this developer, for Tmax400 film, ISO 400 and ISO 800 has exactly the same development time.

Also, for many other films such as Plus-X125, Tri-X400, etc, ISO125/250, and 400/800 are listed together with the same development time.

Why is this? If we change the ISO rating of the camera by 1EV and not change the development time, wouldn't it result in under/over exposure and remain uncorrected in pull/push development?

 

[Nicholas Lindan]

According to Kodak's literature for this developer, for Tmax400 film, ISO 400 and ISO 800 has exactly the same development time.

The increased development time increases the contrast. If film is underexposed then much of the image is in the toe and at low contrast. Increasing the development time increases the contrast so that underexposed images will print at normal contrast.

Kodak has found that better image quality is to be had by simply using a higher contrast grade of paper when underexposing ("pushing" film speed), as opposed to overdeveloping to gain negative contrast.

At great underexposure it does take extra developing time for the shadow detail (such as it is) to emerge.

 

[nworth]

Using, say 0.1 log d as the speed point, the biggest difference I have seen is about 1/3 of a stop between say 100:1 Rodinal and T-max developer.

Your plot illustrates things very well. The film technically has the same speed in both developers, but for practical purposes it may appear to be a bit slower in Rodinal (produces generally less density for a given exposure). Developers can affect speed in a lot of ways by changing the curve shape. Higher contrast developers may sometimes be touted as speed increasing - that's the way push processing works - not because there is an actual increase in speed but because overall density is increased. The ISO speed testing routine specifies certain developers to give a degree of consistency. Some developers actually do affect speed, but usually by only a stop or so. For instance, some high sulfite developers like D-76 show an actual increase in film speed over more standard (in 1950) formulations. Others, like Microdol and especially some PPD developers produce a marked decrease in film speed. This is why photographers a film developer combination before using it for critical applications.

 

[hrst]

Push development is a myth. 1/3 a stop or so is useless. Just use a faster film.

It may boost the darkest shadow details only by 1/3 stop, but that's not the point --- pushing works by boosting lower midtones and midtones and bringing them to the desired level. So, push development is a compromise where you sacrifice shadow details. This speed is still real, true speed in the sense that you can shoot with that faster EI and get results that you are pleased with.

Losing shadow details seems to be quite a wise compromise, since this approach is used in highest-speed films also; the ISO speed for films like TMAX3200P, Delta 3200 is something like 1000 and, strictly speaking, when you process them to the box speed, you are push processing. This sacrifices shadow detail, but it may look much better than with truly 3200 ISO speed film that would have gigantic grain.

 

[Nathan Potter]

Per the OPs' item 1, the rated film speed is based only on an ANSI standard for ASA determination (ANSI PH2.5 - 1972). The ASA speed is equal to a delta log D of 0.8 divided by the luminance dose on the film in lux-seconds sufficient to produce a film density of 0.1 above base plus fog (as mentioned by Goldfarb above). The ANSI specification also states the the 0.8 neg density range corresponds to an luminance range of log 1.3 lux seconds where the point on the sensitometric curve (speed point) of 0.1 above base + fog is at the shadow end of the 1.3 luminance range. (All hard to explain in words!).

But this is simply a standard so that all manufacturers can rate film speed consistently. It turns out that many photographers find that derating the film speed is useful for moving the shadow areas in a scene up into the more linear portion of the sensitometric curve rather than increasing development time.

Nathan Potter, Austin TX.

 

[c6h6o3]

It may boost the darkest shadow details only by 1/3 stop, but that's not the point --- pushing works by boosting lower midtones and midtones and bringing them to the desired level.

It's precisely the point if you're not willing to sacrifice shadow detail, which I'm not. I realize that in increasing development you boost lower midtones; John's Sexton's work is a good example of this. Sometimes his grasses and green foliage are shifted up the scale to Zones V-VI.

But I define effective speed as that point where Zone III comes up off the toe into the straight line portion of the characteristic curve. No amount of increased development will move that in any appreciable way. Only increased exposure will do that.

Actually, I spoke too soon in calling push development a myth. There is one situation in which I do get truly increased film speed, and that is in semi-stand development in pyrocat HD. I don't know why, but with any other process I rate my TMY at 200. With semi-stand, 400. I'm quite pleased with the results along the whole scale.

To each his own.