Page 1 of 3 123 LastLast
Results 1 to 10 of 24

Thread: finding film speed?

  1. #1

    Join Date
    Oct 2003
    Posts
    389

    finding film speed?

    To stop the smart asses among us I know the film speed is printed on the box.

    Can someone please explain how to find the actual film speed. I thought I had a handle on it but as I read more I am definately not getting it. How can a developer increase a film's exposure speed? How can BPF 200 go from Ei200 to EI320(as I read in a post on photo.n#$)in rollo pyro? As I am finding out quickly with an increase in format the increase in cost is pretty much proportional.

    This is what I understand. Posted film speed is a starting point and, like exposure, dictates the amount of lite needed to record the average light intensity. slower speed equals denser neg, higher speed equals thinner neg.

    Anyone shoot BPF 200, and what speed do you use?

  2. #2
    Resident Heretic
    Join Date
    Sep 2003
    Location
    USA, North Carolina
    Posts
    2,944

    finding film speed?

    Two suggested readings:

    Adams' The Negative

    Anchell and Troop's The Film Development Cookbook.

    The first one defines how to perform a film speed test. The second one tells you how various developers effect film speed, among other things.

    The thing to understand is that film speed isn't a constant. It depends on lots of factors, including the developer you use and your processing method. That's why you have to "calibrate" your process, which is what finding your personal exposure index (EI) is all about.

    Bruce Watson

  3. #3
    Whatever David A. Goldfarb's Avatar
    Join Date
    Mar 2000
    Location
    Honolulu, Hawai'i
    Posts
    4,570

    finding film speed?

    The zone system approach is to test what exposure gives you a density value of 0.1 at Zone I and use that as your starting personal film speed.

    Then (after establishing development times) you might evaluate the kind of shadow detail you are getting in your prints, and you might make further adjustments. If the film's characteristic curve has a long toe, for instance, you might decide that a little more exposure gives you better shadow detail without sacrificing highlight detail, so you might lower your EI from the tested speed with that film as a general practice.

    If you don't have access to a densitometer, then you might just look at your negatives on a light table and see whether they have the detail that you want in the shadows. If not, try lowering the EI, and check your prints to see that the highlights aren't getting washed out. If your shadows are okay, but you want thinner negs with finer grain, try raising the EI and see if the shadows hold.

  4. #4

    Join Date
    Sep 2003
    Posts
    537

    finding film speed?

    Mark, you have just received two excellent brief summaries. If you require the lengthy step-by-step details, email me and Iíll send you complete instructions on testing from my old Kodak manuals. Not too difficult, but too lengthy to fit in a simple forum post.

  5. #5
    Tim Curry's Avatar
    Join Date
    Sep 2003
    Location
    Tucson
    Posts
    144

    finding film speed?

    Get a copy of Fred Picker's "Zone VI Workshop." He gives simple, easy to understand directions for film testing with a minimum for fuss and confusing terminology. Here is the short answer to your question.

    Basically, run a series of test exposures with a white wall as your subject. Place your shots on zone 1 as you would meter the wall (not zone 5). Vary the exposure with each shot (asa), but keep track of the film speed as you do. For example: Film is rated at 100 from the factory, but you may run from asa 25 up to asa 200. Develop all film for recommended time with your developer of choice.

    Next, print all film. Use the unexposed film edge to print a maximum black for the minimum time necessary as your guide. Ignore the exposed portion of the film until you have a maximum black. This would represent film base plus fog, or true black. The film which shows the first hint of lightening above this film base plus fog is what you want with this print exposure. This would correspond to zone 1, which was your shot placement with the given asa rating for the film.

    Repeat the test now using this asa rating to develop for zone 8. Place a white wall with some texture on zone 8 and develop until you have a true zone 8 value.

    Different developers act with different characteristics. Pyrocat HD tends to give "normal" speeds. PMK pyro usually reduces film speed by one stop. ABC pyro tends to reduce film speed by 2 stops.

  6. #6

    Join Date
    Jan 2004
    Posts
    7

    finding film speed?

    To clarify, the Zone 1 density value shouldn't just be 0.1, but "0.1 above film base plus fog".

    So first, you would need to use a densitometer to find out the film base plus fog on an unexposed negative. Assuming film base plus fog on the unexposed negative was .1, the proper EI (personal film speed) would be the one used to produce a Zone 1 exposure that resulted in a densitometer reading of 0.2

    In addition to the books recommended above, I would recommend Picker's Zone VI workshop book, which I still consider to be the most concise explanation of the Zone System and its testing procedures.

  7. #7

    Join Date
    Jan 2001
    Posts
    3,956

    finding film speed?

    I rate BPF200 at EI=100 developed in Xtol. Just expose for the shadows and develop for the highlights, like they've said for 125 years. If your negatives don't have enough shadow detail, then increase exposure by 1/2 stop until they do have. If negative areas that should be totally clear are light gray, decrease exposure by 1/2 stop until the negative is virtually clear. Then adjust the development to print on #2 or #3 paper without blown-out light areas. Piece of cake. Have fun.
    Wilhelm (Sarasota)

  8. #8

    Join Date
    Feb 2001
    Location
    Los Angeles
    Posts
    1,773

    finding film speed?

    Mark: I also think Picker's book is the place to start. Different meters and processing techniques give you different numbers, you have to find your speed by testing.

  9. #9

    Join Date
    Oct 2003
    Posts
    389

    finding film speed?

    Thanks for the info but how does a developer increase or decrease film speed?

    Maybe I am just panicking over the idea of a new learning curve for making Pd and kallitype ready negs.

  10. #10

    finding film speed?

    Mark, You just threw in another variable, Pd and Kallitype negs. These negs will need a longer scale to fit the process so you will need to extend development to get there. When you do this you will need to give less exposure because when you extend dev. you will gain some density in the thin areas of the neg. which only makes for long exposure times. One way of giving less exposure is to use a higher film speed on your meter. Good luck, it makes more sense once you use it for awhile.

Similar Threads

  1. finding a tripod
    By Richard Schlesinger in forum Gear
    Replies: 24
    Last Post: 17-Feb-2006, 11:27
  2. Running Film Speed Tests on Color Neg Film
    By brian steinberger in forum Darkroom: Film, Processing & Printing
    Replies: 7
    Last Post: 2-Oct-2005, 13:03
  3. Camera restoration - finding parts
    By Scott Holt in forum Cameras & Camera Accessories
    Replies: 5
    Last Post: 15-Apr-2005, 17:26
  4. Need help finding a 4x5 enlarger
    By brian steinberger in forum Darkroom: Equipment
    Replies: 24
    Last Post: 21-Jan-2005, 04:12
  5. PMK and FP4+ Film Speed
    By Jerry Flynn in forum Darkroom: Film, Processing & Printing
    Replies: 11
    Last Post: 14-Sep-2004, 13:06

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •