Results 1 to 4 of 4

Thread: Exposure correction for bellows, filter, reciprocity

  1. #1
    Laszlo's Avatar
    Join Date
    May 2005
    Location
    Southwestern US
    Posts
    41

    Exposure correction for bellows, filter, reciprocity

    I have developed a Palm software, called LF Exp, that I am using in the field to adjust the exposure for the bellows draw, filter factor and reciprocity failure.

    The central idea is that the light meter info is converted using the given film's EI, and the shot's chosen aperture. As I am using several filters, each film-filter pair is factored in as well. Next, the bellows draw for the shot is entered in the calculation. Finally, if the shutter speed exceeds one second, reciprocity correction is applied.

    The exposure data can be stored in the Memo pad to be printed later.

    I have developed this software mainly to fit my needs, but I am happy to share it with the LF community as a donationware. Please see more (including the disclaimers) here.

    I hope the moderators will be OK with this announcement.

  2. #2

    Join Date
    May 2006
    Location
    Los Angeles
    Posts
    806

    Re: Exposure correction for bellows, filter, reciprocity

    Do you have the reciprocity failure characteristics for EACH film? Keep in mind also - that the actual focal length of, let's say, a 150mm lens is RARELY that... normally up to 5% off... though I suppose it wouldn't make enough of a difference for any but the most exacting applications...

  3. #3
    Laszlo's Avatar
    Join Date
    May 2005
    Location
    Southwestern US
    Posts
    41

    Re: Exposure correction for bellows, filter, reciprocity

    I use 3 BW films (TMX, Pola 55 and Maco infraref) and 2 color films (Provia and Velvia) and have obtained the manufacturer info on them -- usually a pdf document which includes reciprocity and filter factors.

  4. #4
    Laszlo's Avatar
    Join Date
    May 2005
    Location
    Southwestern US
    Posts
    41

    Re: Exposure correction for bellows, filter, reciprocity

    ... and also, re: the 150mm focal length. The precise focal length is not really important. I decided to set the software at 1/3 stop precision, so each adjustment step is on 1/3 stops. Theoretically it is possible that such errors accumulate to become significant but in practice this has not (yet) been a problem.

    For a 150mm lens the first bellows extension of interest (which leads to a 1/3 stop drop off of light) is 168mm, the next one is 188 and then 212 etc. A few mm here and there of focal length or standard displacement are not really important, nor are they easily measured in the field on a wood camera. If such precision were important, bracketing or a digital back on a monorail would be needed.

Similar Threads

  1. Bellows Extension calculation
    By Jonathan Brewer in forum Style & Technique
    Replies: 15
    Last Post: 20-Jun-2010, 14:21
  2. Exposure with filter question
    By linuxpng in forum Style & Technique
    Replies: 9
    Last Post: 7-Jan-2007, 01:57
  3. fp4+ reciprocity failure (and a short question about pre exposure)
    By false_Aesthetic in forum Darkroom: Film, Processing & Printing
    Replies: 16
    Last Post: 4-Sep-2006, 17:11
  4. exposure of dark evergreen trees?
    By Bill Glickman in forum Style & Technique
    Replies: 23
    Last Post: 8-Sep-2001, 05:33
  5. exposure allowance for center filter
    By Chet Wright in forum Lenses & Lens Accessories
    Replies: 1
    Last Post: 1-Feb-1999, 14:53

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
  •