Guide to BW films?

[phenix]

I have to recognize that in my previous comment(s) there was a voluntary inexactitude, issued from my desire to simplify things. Now, I think it is time to be corrected: crystals and grain are different things – the grain is a cloud of crystals, like the ice crystals in a snowflake. These clouds, and not the crystals themselves, are developing 3D or 2D in classic, respective T-grain emulsions. There’s also another detail to be mentioned here: the bigger the crystals, the smaller the clouds they form. And T-grain crystals are bigger than classic grain crystals, so the clouds they form tend to be finer than in classic emulsions (at the same ISO and similar exposure, of course).

Good luck guys, and thanks for your comments!

 

[AgX]

phenix,

as hinted before we seemingly have different conceptions on the structure of emulsions and the way they form the optical effective grain.

But I rather want to draw the attention on another topic you mentionend:

There is a variance between the different image structure different types of emulsion will show, dependend on the degree of stopping down the lens. (As this has an influence on the average angle of incidence of the rays hitting, and penetrating, the emulsion.)

This is very interesting.

However such an effect is reverse-proportional to the back focus of the lens-camera system.

 

[phenix]

phenix, as hinted before we seemingly have different conceptions on the structure of emulsions and the way they form the optical effective grain.

Agx, if you have a disagreement with the technical aspects I wrote about, I can tell you only that my knowledge on films, emulsions, grain, etc, comes from literature and serious forums. But I cannot go deeply, like PE uses to do in advocating technical aspects, as I am not an engineer (chemist, optician, etc…). Still, what I learned, was and still is very consistent with my photographic experiments, so it does make sense for me. But I either cannot contradict you.

Now, you also said something I didn’t understood:

However such an effect is reverse-proportional to the back focus of the lens-camera system.

In fact, all I understand is the "reverse-proportional" issue, but my film broke when it came to "back focus of the lens-camera system". Could you, please, explain it?

And BTW, with this last topic, a new thread could be open: a Guide to lenses. I would have too, some comments to add (similar with the above on film, but even more documented).

 

[Tom Stanworth]

No, no, no, I actually have all the answers. OK, maybe not. My 2 Cents however is:

1. Do pick a sensible combo or two when getting started. pick something pretty bullet proof that lots of people use, lots get great results with and try to get good reliable results. My personal view is to stick to traditional emulsions at the very beginning. I would personally recommend: Fp4+ & TriX/Neopan 400/Hp5+. If in smaller 35mm format, I would drop the HP5+ and use one of the former. I would use either D76/ID-11 (they are essentially the same) or Xtol (diluted 1+1 as a starting point). Any of these combined is super popular and a great place to start.

2. KEEP NOTES on exposure and development details. Once you have gotten to grips with a trad film and std dev, try some new technology films. I personally recommend Delta 100 and 400. The reason is that they behave closer to normal films than TMAX100/Acros etc, yet Delta 100 is miles finer in grain than FP4+ and has biting sharpness. Delta 400 is very fine grained; far finer than TriX and HP5+ with only Neopan coming close (of those I have mentioned. I do not have experience with the new TMY-2). Keep using your std developer so you are only changing one thing at a time. Continue to experiment and see what you think. A good ploy is to shoot a roll of your good ole standby for a scene you like and then put a roll of your new film thru. You have reliable outcome in the form of your old standby and can see how your new film does.

3. Once you have this sorted out, try some different developers. Examples would be a fine grain dev such as perceptol/Microdol and also an acutance dev such as FX-39 etc. Leave staining devs until last.

4. Whenever you get the chance to shoot a test roll and hone your exposure and dev times, do so. Thats what I am doing now before a trip to india, trying to get my exposure/dev times for several films totally screwed down with a new dilution of Xtol (1+2), which I am otherwise familiar with.

Personally I am using a number of films at present: Delta 100, Delta 400 and TriX, Neopan. The reason is this. I am confident using any of the three 400 speed films and I want to shoot real subjects to decide which I actually prefer under real (rather than test) conditions. I have a sneaky suspicion I will decide on one traditional emulsion (Neopan or TrIX) and keep the Delta 400 for when I want really fine grain, with delta 100 as my slow film (IMO it is an epic leap in resolution over FP4+ but is trickier to get right in exposure and devt). So, I will probably come to rest with three films in regular use with Ilford 3200 for exceptional circumstances. There is nothing wrong with using more than one or two films, but don't try to do it in one leap.

Another point would be filters. Do not trust the factors given by film manufacturers. If you intend to use yellow, orange filters etc, get things sorted without filters first (with each film) and then do a test to see what exposure factor you need to apply to get the same exposure with the filter on. I found that with B&W filters, the Med Yellow (8) was supposed to require 1 stop and 1/3 is my personal factor (1 stop is clearly over exposed and 2/3 is a touch over - 1/2 would be perfect actually as +1/3 is a teeny weeny bit out, but more accurate than +2/3)...and the Orange /red (23?) at 2 stop factor actually requires 1 & 1/3 stops.

Other factors come into it later on e.g I like to be able to load 2 x 120 films onto a reel. This is easy with ilford films but can be a pain with TriX and Neopan due to the sticky strip they use to attach the film to the backing paper (it likes to stick to the rails, the film etc - ilford does not extend it so wide on the fils so it interferes with the rails less...and is less sticky). Will I decide on this alone? No. However, if after this next 'final decider photo trip' I find two films I can happily work with, it will be the deciding feature as it makes a difference to economy. A big difference in fact.

some 35mm cassettes are a pig to open and that might sway you when two films are otherwise equal in your mind.

Print, print and print some more. Then try to figure out the relationship between the negs and issues you come across.

A lot that you do will depend on your preferences in the print and also your enlarger. That makes a HUGE difference.

 

[AgX]

Now, you also said something I didn’t understood:

In fact, all I understand is the "reverse-proportional" issue, but my film broke when it came to "back focus of the lens-camera system". Could you, please, explain it?

The idea behind your statement is that when using a lens at full aperture light is hitting the film in most varying angles at the same point of film:

Rays on axis hitting the film perpendicular at frame center, and at the same time corresponding rays originating from the circumference of the back lens element hitting the same point at an angle.

For a point on the film in a corner of the frame there is a difference in angle too; rays from the center have a more shallow angle of incidence than rays originating from the circumference.

As the emulsion has a finite thickness this obviously has got an effect on image forming. Even a typical one for each type of emulsion.

You put further that stopping down would effect different emulsions in a different way.


My remark was intentended to show that any of those effects is dependent on a great variation in the angle of incidence of rays hitting the film.

The back focus is the distance between the back lens element and the film plane.
The greater that distance the more parallel (and more perpendicular) all rays will be. Stopping down a lens with a long back focus will have much less effect on the variation between the angles of incidence, than with eg. a symmetric wide angle lens, where the back element nearly hits the film plane.

 

[AgX]

phenix,

I just reread what has been written by me and you about that stopping down thing. The more I think about it at the moment the more I get confused.
So please take what I said about that very effect of stopping down with a grain of salt... I shall sleep over this issue and perhaps also do some ray-tracing.

As this topic is off the actual theme of this thread we rather could discuss it via PM anyway.

 

[phenix]

...For a point on the film in a corner of the frame there is a difference in angle too; rays from the center have a more shallow angle of incidence than rays originating from the circumference.
...
You put further that stopping down would effect different emulsions in a different way.
...
My remark was intentended to show that any of those effects is dependent on a great variation in the angle of incidence of rays hitting the film.
The back focus is the distance between the back lens element and the film plane.
The greater that distance the more parallel (and more perpendicular) all rays will be. Stopping down a lens with a long back focus will have much less effect on the variation between the angles of incidence, than with eg. a symmetric wide angle lens, where the back element nearly hits the film plane.

AgX, thanks for these explanations. They emphasize details I didn’t thought at, and were very sense and truthful. Thus, I think the back focus distance and the diameter of the rear element are the most influent factors in determining the angles the light beams are touching the emulsion (at closed down apertures, because at open wide, light beams are traveling in al senses). And these angles and the type and size of the grain are determining the half-shadow effect inside the emulsion layer(s), effect that decreases the acutance. Did I match your contribution and mine in a meaningful way, or am I wrong with something?

Now, I have another question: the half-shadow effect takes place when opening large the aperture, because of the light beams traveling in almost all directions. And I would add here that a wide-angle lens would increase this effect. But the same effect will take place too, when closing down the aperture, again especially with wide-angle lenses, because (this time) of the small back focus distance and usually the small rear element. Well, than it seams, that the aperture value has no influence on this effect, but only the focal length of the lens. The aperture would only change the image quality according to the MTF diagram of the lens, not by influencing the half-shadow effect inside the emulsion layer(s). Am I right with this, or did I made a logical shortcut somewhere?

Thanks again for your contribution.

 

[Marco B]

I think this discussion veered a bit to much of it's original topic. To get back to the main topic of a guide to BW films, I have now made scans of the good document that used to be available of the Silverprint website. They probably took it of since a lot of it is outdated, however, even the older film types that may have been succeeded by newer versions (like updates on TMax), still give important info as the main purpose of films usually does not change with a change / update of emulsion.

This is a 7 page document discussing a whole bunch of BW and color films and the purpose they were designed for, in a very brief but clear manner without going into unnecessary details. I have put it on my website, and you can download it here (unfortunately only in Word format, as I don't have a PDF converter, the file is almost 10MB due to the page scans, so be warned):

Guide to BW films from Silverprint

And for those wanting to continue the discussion about emulsion and grains, I found this document from Tim Vitale one of the best documents actually explaining and showing the structure of of BW and color film using scanning electron microscope images:

Film Grain, Resolution and Fundamental Film Particles by Tim Vitale

Marco