Film Speed Question

[eric_reid]

Ok, I've looked through the archives and have seen a lot of info on

this but I'm still confused. I've had my M6TTL for about a year now

and I have had excellent exposure results using a wide variety of B&W

and color neg stock (not always great pics, but excellent exposure

results!). For B&W, I am planning on returning to Tri-X as my

primary stock (found the Delta 400 terrific in terms of grain and

tonal range, but just not punchy enough for my style when using 400

spead B&W), continuing with Delta 100, and with Delta 3200 when

applicable.

 

Here's the question: I have pushed and pulled the 400 and 3200 speed

films with success but ALWAYS matching the exposed push/pull amount

with the lab developing instruction (i.e., if I push one stop, I

instruct the lab to do the same). I've read a number of posts from

people on this forum who seem to know what they are talking about

that they routinely seem to pull their high speed B&W neg yet process

normal. The two examples I see most are (i) shooting 3200 at 1600

and then processing at 3200, and (ii) shooting 400 at 320 and then

processing at 400. I don't get this. How can the exposure be

correct? I know these films have good exposure latitude, but I don't

understand being a full stop off (3200 to 1600). What is

particularly confusing is that I thought, if anything, you want to be

overexposed, not under and wouldn't the above technique bring you

consistently under? Note, I'm using a good, pro lab and they will

understand and follow any instructions I give them. Thanks in

advance for your answers.

[al_kaplan1]

The speed rating works great for taking pictures of grey scales and color patches after you take your reading off an 18% grey card. We take photos in the real world, our metering habits differ, our subject matter differs, even our darkroom thermometers may be off a bit, and no two people agitate the same.

 

We could tell ourselves that we should open up (or close down) 1/2 stop from our reading for any of the above reasons. It is a lot easier to just change the ISO on the meter. Five photographers might use 5 differant ISO settings when metering the same scene and all use the same exposure. Or one might like a bit more "punch" in his negatives, over develop slightly, and choose a higher ISO. Use what works for you.

[roger_michel]

eric -- i hate to be th eone to open your eyes to the seamy side of emulsion marketing, but many films have a true speed that varies from their posted ISO. most people find that tri-x has a true film speed much closer to 300 than 400. when i say true speed, i mean the iso at which, applying standardized exposure measurements, the density characteristics of the negative will conform to spec. in point of fact, exposed at 400, tri-x lacks the shadow density claimed in kodak materials. likewise tmax 3200 is probably closer to a true 1200 speed film, again in terms of its ability to develop density according to industry standards. needless to say, the films can be pushed beyond their true speed. however, doing so will always come at a contrast cost -- specifically a loss of relative shadow detail.

[Aoresteen]

Eric,

 

Forget what the instructions say. Run your own tests and stick to them.

 

Read Fred Pikard's book "Zone VI Workshop". You need to do two tests.

 

1. Film speed test. For your meter, water, camera etc.

 

2. Development time test to find the correct time for that film speed to place a Zone VIII (ok, real white) tone.

 

The tests don't take long to do. I check my test with every new batch of film I buy. That's why I buy 50 roll pro-packs of HP5 (less testing!)

[todd peach seattle, washi]

<i>

shooting 400 at 320 and then processing at 400. I

don't get this. How can the exposure be correct? I know these films have good exposure latitude, but I don't understand being a full stop off

(3200 to 1600). What is particularly confusing is that I thought, if anything, you want to be overexposed, not under and wouldn't the above

technique bring you consistently under?

</i>

<p>

You're doing the math backwards (easy enough to do): Rating 3200 film at 1600 and processing normally results in a stop <i>more</i> exposure.<p>

[roger_michel]

that's fred picker. sadly he died relatively recently. his zone vi video series is quite good.

[eric_reid]

Todd,

 

I think you're right on my math, but help me out with this - if I set my camera's ASA dial at 1600 for 3200 film, my camera's meter will "think" there is slower film than there is and it will show meter readings resulting in overexposed film (as you mentioned) - but then what happens when you go to develop it as if it were 3200?

[roger_michel]

eric -- when you say "got ot develop it as if it were 3200" i take you to mean "develop the film, exposed at 1600, at the times indicated for the film when rated at 3200." in that case, you will possibly (although not necessarily and not to a great extent) cause some blocking of hi-lites. rated at a lower ISO, and developed at a time optimized for that ISO, you will get more shadow detail with the same hi-lite detail. you havre to understand, you can't push film at no cost. while it is possible to get the mids and hilites with adequate detail (altho the mids go to at a point), as you push the shadow detail disappears. true speed is the iso at which, applying some development regimen, shadow and hilite density match standard specs. above that (i.e. pushed), and shadow detail will not be up to spec.

[william_m._carson]

You've got a lot to learn about TRI-X! If you process it with D-76 1:1, for 7½ minutes [agitatiuon 3 or 4 sec. at 30 sec. intervals]at precisely 68°F on all solutions including wash. Try it; you'll like it!

[todd peach seattle, washi]

Eric -

 

I'm no expert on 'pulling' film, I'm just aware that folks do it, and thought I'd jump in and point out the 'sign error' in your thinking, thus dragging you back to 'overexposure might be OK'. I don't even own a Leica, just a lurker/wannabe.

[carl smith]

This is called rating, and is a good practice to get involved in to maximize the quality of your images, particularly with certain films. As mentioned, the main reason is because the films are packaged at one speed, but their color saturation (for color films) and other performance characteristics are improved at slower speeds of 1/3 stop slower or more.

 

Also, you have your terminology backwards. If you shoot 3200spd film at 1600, or 400spd at 200, you are overexposing by a whole stop, not underexposing.