Set film lower than rating?

Discussion in 'Black and White' started by brandon_andreadakis, Jun 26, 2009.

  1. My photo teacher told me to always set my camera for an ISO lower than the films rating in order to give better negatives, is this true? For example she told me to always shoot ISO 400 film at ISO 200.
     
  2. Some films are very good at this. Tri-X at 200 is a good one, and Foma 200 at 100. Other, not as much. It's usually not really necessary. Look at dev time charts because you might need to adjust the time to avoid overexposure.
     
  3. In negative film, I can't see that it does much but make a harder-to-print negative. Maybe that's just me. There was a day of high variability in films, cameras, and processing that the manufacturers rated films lower than they later did, and it might be some sort of ancestral memory at work here....
    For color slides, on the other hand, many people like the darker, more saturated colors that come with slight under exposure, so many people shot ISO 25 Kodachrome at ISO (actually ASA) 32 in the days back when.
     
  4. Depending upon the lighting you can gain additional shadow detail. If lighting is flat you might not want to downrate it. For example, I usually expose Plus-X at box speed, but under flat lighting or overcast days I rate it at 200.
     
  5. Over exposed negatives look good as you hang them up to dry, but a correctly exposed negative prints best. So no, use the box speed IMO.
     
  6. there was a Modern Photography article about taking photos at or before sunrise or omn misty days and rating asa 25 at 32.
    it incerased saturation when there was flat lighting few shadows and lower visual contrast
    with negative B&W film there was a 2x safety factor. in the 1950's.
    most B&W films were rated at half speed.
    tri-x at 200 not 400.
    many advanced amateurs and pros rated the film at 400.
    when kodak rated the film at 400, there was no change in the film.
    just the rating.
    slide film can only be FUDGED a little when the lighting is flat.
    the newer color negative films are quite flexible.
    back then there were only kodacolor films in roll film sizes, no 35mm!
    and one of the instructions ( then) was to use "direct sunlight"
     
  7. Yeah, and wasn't ASA 12 considered fast for a color film? :)
    It's true, current color negative films have remarkable exposure latitude. Somebody on the forum posted a test a while back where he overexposed Ektar by 0, 1, 2, 3, 4 stops... it took a while before you started seeing real problems.
     
  8. When fast color negative films began to improve, many users discovered that exposing at a lower E.I. gave finer grain and better color saturation. I'm sure that the lab really made a difference here. I usually rate Portra 160 VC at E.I. 125 for weddings (E.I. if church has dark walls). YMMV, though as some labs that receive down-rated film will deliver washed out prints or scans.
     
  9. Not always. It depends on the light and thus the subject brightness range. On a bright day I typically downrate film by 1 1/3 stops (e.g. HP5 at 160 ASA or FP4 at 50 ASA) and then cut development by 45 percent. It will give you a negative with a longer scale of tones.
     
  10. If you search for 'finding your personal film speed' you will find lots of articles about doing tests at varying exposures and developing for various times until you find a combination that suits your methods.
    I didn't bother with doing the tests myself as I noiced that nine times out of ten, the results were to halve the ISO and reduce the development by 20-25%
    I tried that with HP5+ and liked the results so continued doing it.
     
  11. The additional exposure from rating a film as slower increases shadow detail. And the corresponding decrease in development keeps the highlights in control.
    B&W film is versatile. There's more than one way to get good results.
     
  12. I've shot Fuji 800 speed color film at ASA 200 and developed it normally with no problems whatsoever!
     
  13. Depends on the developer/film combination, if you're talking about B&W. For instance, my testing indicates that most films need to be shot at lower than box ISO when developed in HC-110, but not in Xtol.
     
  14. This is probably a variety of the old adage to overexpose and underdevelop (cut time). Idea is to build up a negative that is a little more dense than standard, to be able to print some details. It's a scheme that works best with a similar or counteracting adjustment in the wet chemistry side.
    Overall, modern materials have, in my imagination, a better range than the older films. A lot of this advice was espoused at a time when films weren't made as sophisticated as they are today. I think you will see a historical grounding in this advice from around 1940s and 1950s. The materials that we are using today are more refined. Some aspects that took a little wizardry to get might fall more within "regular" use of contemporary materials. I say all this, just having read through older books; I was not a photographer back in the 50s or anything.
    For example, Ansel Adams espoused this approach a lot; yet, he was working primarily with sheet films in the 1930s. Even he noted changes in responsiveness in films as his career continued. If you look at the books he put out, I think, in the 50s, and then read some of his later editions, there are some subtle changes in his processing recommendations. He noted a change in the thickness of film bases, for example. He felt those film structure changes were significant enough to note some changes in exposure and processing advice. Overall, though, it's still an okay approach; overexpose and under-develop.
    I don't know it for a fact, and could be wrong, but I am of the opinion that it's a lot easier to get good results out of contemporary materials than it used to be. You can probably do with standard exposure schemes and ordinary materials what would have taken some doing 50 years ago.
    It's good advice, for an approach, but I wouldn't say it was absolutely required or anything.
     
  15. Yeah, and wasn't ASA 12 considered fast for a color film? :)
    Not so much "fast," as acceptible. I started with Kodachome (ASA10, quickly moved on to the (F) ASA 12 version and was not so sure about Kodachrome II (ASA 25). There were faster slide films from Ansco (later, GAF), and Agfa, even Ektachrome, etc. At least by the late 50s some of these were at (gasp!) ASA 32.
     
  16. Yeah, when Super Anscochrome debuted (ISO 100) I'm surprised Ansco didn't put racing flags on the box. This film was heavily advertised until High Speed Ektachrome de-throned it as speed champ.
    Back to the original subject: I've heard it said, "expose for shadows, develop for highlights." I think exposing at a lower ISO rating does that. Again, you should take the type of lighting into consideration. In the B&W safety factor days previous to 1960, the recently improved Plus-X had a box speed of ISO 80, but many users recommended an E.I. of 160 to 320 for best results. Just like today, the box speed is a starting point and the user should determine what works best.
     
  17. Here's the deal with that. Since most negative films have tremendous over exposure latitude, using a lower exposure index does not do much harm. In cases where the lighting is harsh, doing so can be helpful in retaining shadow detail. In short, over exposing the film helps to make up for meter induced errors without sacrificing too much image quality. Now is this necessary? In most cases, no. Films from Kodak, Fuji, and Ilford perform exceptionally well at the rated box speed. Rating films from these companies at box speed will produce optimal results in standard developers when photographing front lit subjects. Back lit subjects require an extra stop or two of light, no matter the film. If you want to emphasize the part of the subject that is in shadow, extra exposure is also called for. FOMA films have optimistic box speeds in my opinion, and a quick look at the data sheets for thses films confirms my anecdotal observations. Your photo instructor is not giving you the whole story. Kodak's data sheets for B&W films are loaded with information that spans brand loyalty. Read them.
     
  18. I was told that on some films, like tri-x, the actual rating of the film is 320, not 400. So many of us shoot it there, but it doesn't make a lot of difference.
     
  19. I've found shooting Velvia 50 (original emulsion) at lower ISO to yield almost cartoonish saturations, but jeez they look great on a lightbox or a cheap projector with a bed-sheet screen....have fun with it. br
     
  20. Ten different photographers will tell you ten different things. Different people are convinced that certain different things are right because it works for them. Unfortunately, we don't know if their light meter is out, if their development temperature is off, if their agitation method is strange, etc. There are no concrete rules, but until you know exactly what you are doing, and how to properly test these things yourself, the best place to start is at box speed. Shoot ISO400 film at 400.
     
  21. I've found shooting Velvia 50 (original emulsion) at lower ISO to yield almost cartoonish saturations, but jeez they look great on a lightbox or a cheap projector with a bed-sheet screen....have fun with it. br​
    What do you mean? I understand cartoonish looking photos with HDR, but I don't follow the above statement.
     
  22. What your teacher has told you is a blanket safety precaution for you students. In other words, a safety net. It is not an absolute. You guys are in the learning stage and will make plenty of mistakes. By downrating film, your ISO 400 at an EI of 200, (there is only one ISO for a given film; the EI is Exposure Index and is the speed you use personally) you are using the latitude (flexibility) of the film to cover some exposure mistakes.
    It's probably a good idea to do this for now, but realize that not every lighting situation or contrast situation will call for this.
    As stated above, you can read about personalizing your film speed to suit your needs.
     
  23. For me it's all in how you are printing. If I scan I find things are not as fussy. Vuescan digs deep into the shadows and often I can expose at box speed. Wet printing is another animal. I recently shot PanF 50 @ 50 because of almost bright overcast conditions. (D76 is certainly not a speed developer) Scanning the neg worked out fine but the enlarger did not like the shadows at all. They went black quick. ISO 25 (maybe less) would have worked out a lot better. I say open the shadows with generous exposure and take it from there.
     

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