Developers and true film speed

[olivier_reichenbach]

When I read that such and such developer "does not give true film speed", does that mean

that if I shoot at the nominal value of my film (let's say Tri X at 400) and then develop

"normally", it'll give me an underexposed negative, as if the film had an actual speed of

only, say, 200?

 

Thank you for helping me clear my way through the jargon of processing,

[kaiyen]

Essentially, yes. You'll have insufficient shadow detail if you shoot Tri-X at, say, 400 when using Rodinal (I think everyone would agree that Rodinal would not yield an EI of 400 for TXT). The "speed" of that film in such and such developer is the EI that you rate the film at which you obtain sufficient shadow detail.

 

allan

[olivier_reichenbach]

Thank you, Allan. Now, would you say that Perceptol - and now, obviously, Rodinal

- would fit in that category, and if I want to use them I should downrate my films, say, one

stop? And what other developers would behave the same?

[al_divenuti]

Microdol-X and Perceptol when used undiluted or 1:1 will cost you about a stop.

 

In truth, relatively few developers are found to give the speed on the box (i.e. an EI that matches its ISO rating). I've always found that Tri-X works best at 250 or 320 in most developers.

 

However, there are some developers that will allow you to rate your film at box speed or maybe higher at normal contrast (i.e. no push). I'll divide these into groups:

 

 

"Standard" Phenidone-Hydroquinone Developers: These developers should produce normal or fine grain even at an EI of 400 for Tri-X.

 

Ilford DD-X, Kodak XTOL, Kodak TMax, Edwal FG7

 

"Speed-Enhancing" Developers: These developers typically are designed to work at above box speed EIs at a reasonable penalty in grain. Again, this is developing to normal contrast:

 

Acufine, Diafine, Ilford Microphen

 

Diafine and Acufine, incidentally, we're basically created for Kodak Tri-X and most report that they perform superbly in low-light conditions and can deliver an EI of 1000 or even 1250 with just a marginal grain penalty. Microphen seems to work well with most films and probably can give you an honest EI of 625 with Tri-X without a push. Sadly, Microphen may no longer be available...at least in the short-term.

 

I'm sure that there are others from Tetanal, Clayton, and others that could be included in both lists.

[kaiyen]

Olivier,

I'd probably start off overexposing by 2/3 of a stop or so with something like Perceptol or Rodinal. Then meter a shadow, expose, develop, and see how it looks. Do you have as much shadow detail there as you had hoped? If not, then overexpose a bit more. If you have more than you want (tone is lighter than you had visualized), then bring it back towards box speed.

 

Al's post lists many of the characteristics of those other developers quite well. One of the reasons why D76 is so commonly used at the start is because it gives a good combination of speed, grain, and sharpness. Not perfect in any of those areas, but pretty good.

 

allan

[roger_hicks1]

Dear Olivier,

 

There's a vast difference between true ISO speeds and the speeds you are happiest with, and a lot of people confuse the two. ISO speeds are very strictly defined, with certain assumptions about flare, subject distance, etc. The basic definition covers shadow density (0.10 above fb+f) and contrast (gamma approximately 0.615).

 

Most 'middle-of-the-road' developers such as Kodak D-76 give the true ISO speed of most films UNDER ISO TEST CONDITIONS. The best speed increasing developers such as Ilford Microphen or DDX or Paterson FX50 give +2/3 stop or a fraction better. All fine grain developers give more or less speed loss: at least 1/3 stop.

 

If you meter the shadows (an assumption inherent in ISO speed definitions) you can usually get away with the ISO speed. If you use any other metering system (ttl, incident, grey card) you may or may not find the ISO speed suitable. For subjects with a low brightness range the ISO speed will normally be more than adequate. For a long brightness range it will without question be too low.

 

This is not a subject that can be covered in a few words and at the risk of self-aggrandisement (check www.rogerandfrances.com and our book PERFECT EXPOSURE) I'd suggest that you research the subject reasonably deeply before accepting anyone's advice, including mine.

 

Cheers,

 

Roger

[spanky]

I've been thinking this same question myself. I like Rodinal but I could never understand when people would write about the speed loss.

I'm still unclear, but I'll be taking another class this spring and hopefully I can talk my instructor into helping me perform some of the film tests I read about in my photo technique books.

Cheers,

Marc

[sassan_hazeghi]

Well, if the "true" film speed is what produces ~0.1 density for a Zone I exposure, I have yet to find an ISO 400 film that comes close to its rated speed with D76 1:1, or Xtol 1:1. I have a relatively slow lens (f/4.5) and would really like to find a true ISO 400 film with either of the above developers (have tried Delta 400, HP5+, 400Tmax, 400TXP, and Neopan 400 and they all seem to be in the ISO 200-250 range according to the density test.)

[jay_de_fehr]

Sassan,

 

have you checked your shutter for accuracy? How about your thermometer? How much flare are you getting? What CI are you developing your test negs to? What kind of lighting are you using for your test exposures? Are you using deionized water in your developers? How do you agitate your test films? There are lots of variables that might affect your results.

 

Jay

[roger_hicks1]

Dear Sassan,

 

What sort of sensitometer (not densitometer) are you using? And what sort of contrast are you developing to? ISO speeds are valid only at the stated G-bar/C.I. This is why I went into the whole question of film speeds in some detail in my book Perfect Exposure (David & Charles/Amphoto, recently reprinted).

 

If you are not directly measuring the light levels and using a sensitometer, in-camera tests are VERY prone to variation as a result of lens/body flare. With in-camera tests, assuming you are shooting real subjects or even grey cards, there is also the question of how you are metering: anything except spot metering of the darkest shadow in which you want detail is substantially worthless for in-camera EI determination.

 

I apologize for stating the obvious and by implication impugning your methodology, but I would be astonished if any of these films (except the original Delta 400, now long replaced) were not VERY close to their nominal ISO speeds, provided, as I said, they are tested under ISO conditions.

 

This after all is why ISO speeds exist. They are not perfect; they are only a starting point. But I get more than adequate shadow detail from HP5+ at 400 or even 500 with the film developed in DDX. Except, bizarrely, with one lens; the 35/5.6 Apo-Grandagon, where I need a stop extra. Why? Dunno. Funny shutter? Vignetting? It doesn't matter, after all.

 

I am not saying that any of these results -- yours, mine or ISO -- is better. All I am saying is that ISO tests are standardized, internationally agreed and replicable by any reputable sensitometrist. Your tests and mine aren't: we're using speeds that suit us, arrived at to suit our equipment and methods.

 

Incidentally I am intrigued by the f/4.5 aperture as there aren't many top-flight lenses with this focal length, though of course there are classics such as the Biogon and the Apo Lanthar and as far as I recall some Xenars and Tessars were f/4.5.

 

Cheers,

 

Roger

[olivier_reichenbach]

Thank you all for your replies.

[stwrtertbsratbs5]

I just shot film curves for Ilford HP5 (ISO 400) and found that exposing at ISO 200 produced a very nice zone 1 exposure for my camera/meter combination (I'm taking a zone course at the New England School of Photography). The instructor recommended that we set our meters at ISO 200 for 400 speed film as a starting point, and it seemed to work for most of the students. Some folks did need to adjust, but most were fine at 1/2 the rated ISO.

 

Robert

[sassan_hazeghi]

I did not mean to detract from Olivier's original question but regarding the ISO 400 films being overrated, my experience has been with several different cameras and lenses (Nikon F3 & F100 and Mamiya 7-II; both of the Mamiya 7 lenses are f/4.5!) but limited to the two developers I mentioned (Xtol 1:1 and D76 1:1). The densitometer I am using could be off, though once calibrated, it seems to read the density of a Staufer's step wedge accurately.

 

Also, I aim to develop close to the standard(?) .6 CI but I have been using ``.06 to .1'' Zone I density as the primary indicator for the film-speed. After all I can control the CI by changing the development time but not the density of the shadows. Incidentally, the observation (again using Zone I density as the main criteria) also applies to a few ISO 100 films I have used (notably Neopan 100 Acros which seems a perfectly good-but-slow ISO 50 film.)

[roger_hicks1]

Dear Sassan,

 

Thanks for the post, and for the reminder that the Mamiya lenses are f/4.5; I should have thought of that. Duh!

 

Your methodology is no doubt ideal for establishing a personal EI but as long as you are doing in-camera testing and using Zones you are not actually determining ISO speeds, as I am sure you are aware -- that was why I asked about a sensitometer and not a densitometer.

 

On comparison testing (the only sort I am equipped to do) I would agree that Acros is indeed the slowest of the nominally ISO 100 films: on a comparison basis I reckoned ISO 64, with the best results (visually) at EI 50, whereas I am assured by those who have the equipment and expertise to do true ISO testing that it is ISO 80 at best in many normal developers.

 

It is very common to rate films at slower than their nominal ISO and I would not wish to discourage anyone from doing it for one moment if that is what gives them the best results. But I do wish to make two points very strongly indeed.

 

The first is that it is important to distinguish between EI and ISO, because ISO speeds are internationally agreed and replicable and personal EIs aren't. If you think I am overly excited about this one, you should hear the views of a friend who is on the ISO standards committee.

 

The second is that while many people find that they get the best results from lower EIs, others are happy (and produce excellent results) with the nominal ISO and a few find they can use still higher speeds especially with true speed increasing developers. But the novice is all too often inclined to accept as gospel the statement that "films aren't as fast as their nominal ISO speeds" without understanding what that statement might mean -- or that in ISO terms the speed is almost always stated correctly.

 

But only almost always, and for a given value of 'correct'. If you plot the curves for Paterson Acupan 200 in almost any developer they almost exactly overlay Ilford FP4 Plus: it IS an ISO 200 film but only in speed-increasing developers, just like FP4. And if you check Foma's spec sheets on this you will see that they admit as much, but only in the curves, not in the text...

 

It is quite legitimate under ISO rules to use any developer, provided you state what it is, but most manufacturers use middle-of-the-road devs (especially D-76) for obvious reasons. ISO speeds are commonly rounded to 1/3 stop and in most cases they are rounded up (surprise! surprise!) though FP4 is an exception as it often runs a little faster than 125.

 

The last point I would make is that ISO speeds are not really important EXCEPT as a starting point. Personally I don't care what the true ISO is: what I care about is what gives me the results I like most, and from film to film this may well vary to different degrees (and in either direction) as compared with the ISO speed. The huge advantage of ISO is that it gives an internationally agreed starting point for personal testing, without too much interference from the marketing men.

 

Cheers,

 

Roger

[roger_hicks1]

Dear Robert,

 

You will see from the post above why I suggest that you point out to your instructor that he is recommending an exposure index or EI, not an ISO speed.

 

Cheers,

 

Roger

[stwrtertbsratbs5]

The sloppy terminology is mine, not my instructors. He referred to EI, so I stand corrected.

 

Robert

[roger_hicks1]

Dear Robert,

 

My apologies for sounding schoolmasterish in my previous post, but I believe that this is a distinction well worth making, which is why I am glad your teacher made it. Many who fail to make it go on to make other errors too.

 

Cheers,

 

Roger

[martian bachelor]

Here's what Ilford says in many of their datasheets:

 

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

 

God and Ilford only knows what they mean by "practical evaluation of film speed".

 

I agree with the others that film speeds these days are generally over-stated by the manufacturers. I don't shoot the 400 speed films but rather the 100/125 speed films. By downrating them the better part of a stop you certainly won't burn `em up. And it shortens the development times some, which is a much bigger savings in time than some fraction of a second during exposure!<g>

 

'Tis better to over-expose than under...

[stephen_benskin]

Hi Roger,

 

Long time. I would like to second your well said statement and add I happen to have an article in the current issue of PHOTO Techniques that deals with this very topic. It's titled <i><u>Flare and Accurate Film Speeds</i></u>. My premise is the discontinuity between the ISO speeds and speeds from Zone System testing originate from a fundamental misconception within Zone System methodology. If you follow the traditional ZS method of film speed testing, you will produce speeds more in line with the pre 1960 standards. The basic premise is that the film speed point isn't necessarily the point of desired exposure, but only a point to define the film speed (explained in more detail in the article). If you think about it, Zone I is four stops under the meter reading or meter calibration point. ISO speed is determined at 3 1/3 stops under and also assumes a certain amount of flare.

<P>

I'm also currently working on an article that describes the contrast parameters of the ISO standard as a version of the fractional gradient method masquerading as a fix density method and not a capitulation to those who found the fractional gradient method too difficult. As you know, any fixed density method will tend to overrate film developed to higher CIs and underrate film developed to lower CIs. The interesting part that I discovered is that film speed based on the frational gadient method changes very little with development. Yes, the overall densities change. Higher CIs will produce a negative with an overall higher density, but since the fractional gradient method is based on gradient and not density, the film speeds don't change much. (This tends to negate the just noticable black concept of standardized printing time.) This is probably why the original fractional gradient method didn't specify a degree of development. It only stated that the film be developed to an average gradient in excess of 0.50. Anyway, the contrast parameters of the current ISO standard are really variables in an equation that defines the difference between the fixed density speed point and the fractional gradient speed point. I feel that if this weren't the case, there would never have been international agreement on a film speed standard. Very interesting stuff.

[daniel_jolicoeur]

Stephen, I just read an article a couple of weeks ago while browsing at Borders, Perhaps you wrote it? It was very well written, I can not remember the name of the magazine; maybe it was View camera techniques, but it was saying the same thing about the zone system error and flare. From what i understood in a quick read was that the zone system was inherently developed off by 2/3 of a stop. It made sense that most people would come out with just about that or a stop lower in there personal film speed. I didn't understand why flare would have anything to do with this, but i just accepted the fact that personal film speeds where off by 2/3 of a stop, so why not take everbody's advice and half the stated ISO rating; being 1/3 of a stop conservative. Am I making sense? I am almost positive you wrote this but my memory is failing?

Regards,

 

Dan

[daniel_jolicoeur]

My appologies it was your article in PHOTO Techniques, sorry for the miss quote. I noticed the name looked fimialar because i wrote it down on a reciept i had in my wallet. I was going to quote what you had written.

Nice Job, sorry for the confusion,

 

Dan