Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Reciprocity Test with ND1000 Filter

  1. #1

    Join Date
    Apr 2020
    Location
    Washington, DC
    Posts
    85

    Reciprocity Test with ND1000 Filter

    Hi all --

    I could use some help with reciprocity: next week I'll travel to the ocean for a few weeks to go on vacation. While there, I thought I'll take some pictures of seascapes with my 4x5 camera on FP-4 with long exposures, keeping Hiroshi Sugimoto's "Seascape" images in mind.

    Before I hit the road I did some reciprocity tests. All images were taken with my 4x5 on Ilford FP4 on a sunny day. I scanned the "Sunny 16" negative (no filter) first and kept the scanner's exposure setting while scanning the other negatives. The screenshots are from the un-corrected FITS files in Photoshop.

    Left, top: "Sunny 16" image.
    Left, bottom: same but with a red filter and compensating for +2 stops. Worked. Looks a bit dark, but that could easily be corrected in Photoshop by tweaking the levels a bit.

    Middle row: ND1000 filter (10 stops) with -1EV and +1EV bracketing, taking Ilford's reciprocity correction into account. Worked out.

    Right row: ND1000 filter + Red filter with -1EV and +1EV bracketing, taking Ilford's reciprocity correction into account. The images are too dark, even if I correct for 12 stops and reciprocity, and have a very high contrast, much more than you would expect from the red filter alone. According to Ilford's reciprocity table, this should have been a 60-sec exposure (ND1000+Red = 12 stops). The bottom right is 80 sec, maybe 2-min would have been better? The contrast is extremely high, much more than you'd see from one of the filters alone (ND1000 or Red). Is this the combined effect of a ND1000 plus a Red filter?

    What's your typical exposure time for ND1000 filters?

    Thanks,
    Stefan

    Ilford FP-4 Reciprocity Test by Stefan Immler, on Flickr
    Last edited by giganova; 16-Jun-2020 at 11:21.

  2. #2

    Join Date
    Aug 2005
    Location
    Illinois
    Posts
    42

    Re: Reciprocity Test with ND1000 Filter

    Ok... So I'm no pro, but you have a 10 stop ND filter plus 2 stops of red filter = 12 stops.
    With no reciprocity taken into account this gives a 60 second exposure.
    According to the recip tables for FP4 Plus this would give a corrected exposure of ~174 seconds (using the formula given).
    So you're a bit more than 1 stop underexposed for your 80 second example.

  3. #3

    Join Date
    Sep 1998
    Location
    Oregon now (formerly Austria)
    Posts
    2,652

    Re: Reciprocity Test with ND1000 Filter

    A couple of things may be throwing wrenches into the works here and giving you results you don't expect.

    First, reciprocity-failure-correction tables in the data sheets packed with the film are just averages. For more accurate factors for Ilford films use the factors in this document: https://www.ilfordphoto.com/wp/wp-co...mpensation.pdf .

    You can see that you'll need a calculator that does powers, but every smart phone has one these days. If I were you, I'd make a table that I could refer to for the film(s) you use based on the Ilford data and use that instead of calculating every time.

    Second, how we meter is really important and one of the big variables in calculating reciprocity-failure corrections. If your initial meter reading is "wrong" (not really wrong for you, but somehow not synced with the norm used for the correction factor) then all the compensations will be wrong too. If you consistently end up with underexposed long exposures, then rate your film a bit slower and go from there. Note that the error introduced by metering "wrong" grows with the length of the total exposure.

    Keep in mind that all of this correction is very dependent on things that vary greatly from photographer to photographer or with the scene, such as personal E.I., metering technique, changing light, processing, etc. To be really accurate, you need to run tests, like you're doing, and make changes until things come out right most of the time. Changing your E.I. for metering long exposures, mentioned above, is one of them. You can also change the factor used to calculate the correction, using a higher one if needed. And, when in doubt, you err on the side of overexposure. Adding 10 minutes to a 20-minute exposure only gives you about an extra 1/3-stop exposure when the reciprocity failure is figured in...

    Another thing to consider is that when you use a lot of compensation for reciprocity failure, the contrast on the negative increases. That's because reciprocity failure happens more for the shadow values than the highlights. The more correction, the more contrast. How much more contrast builds up with extended exposure depends on the film, though. Some old-fashioned and modern conventional films require development changes (reductions) with larger corrections. My rule of thumb used to be one N-number less for every doubling of the corrected exposure time from the time indicated on the meter, e.g., if the meter reads 15 seconds, and my total exposure has to be 30 seconds according to the reciprocity-failure-correction table, I'll then reduce development by one N-number, e.g., N would become N-1. This worked for many films in the past, but most films I use nowadays seem to need less development changes than that. Still, you could use that as a starting point.

    Now to your filter: I don't know which red filter you are using, but the standard #25 filter has a correction factor of 8, or 3 stops. You only used two (maybe you have a #23? or something else?). It looks to me, though, as if you simply didn't compensate enough for the red filter.

    At any rate, red filters introduce more contrast with some films due to the differing spectral response of the film's emulsion. You may need to experiment with and without the filter and come up with a "fudge factor" for the filter as well (which you would apply before figuring reciprocity-failure correction).

    Hope this helps a little,

    Doremus

  4. #4

    Join Date
    Apr 2020
    Location
    Washington, DC
    Posts
    85

    Re: Reciprocity Test with ND1000 Filter

    Great input, thanks! I am using a B+W 090 Red filter and correct for 2 f/stops. But you are right, maybe 3 stops would be more appropriate.

  5. #5

    Join Date
    Apr 2020
    Location
    Washington, DC
    Posts
    85

    Re: Reciprocity Test with ND1000 Filter

    Quote Originally Posted by Robert Tilden View Post
    Ok... So I'm no pro, but you have a 10 stop ND filter plus 2 stops of red filter = 12 stops.
    Yes, 12 stops.

    With no reciprocity taken into account this gives a 60 second exposure.
    According to the recip tables for FP4 Plus this would give a corrected exposure of ~174 seconds (using the formula given).
    So you're a bit more than 1 stop underexposed for your 80 second example.
    Ah, yes, of course! I had a mistake in my Excel spreadsheet where I corrected for reciprocity. I also get 174 s = 3 min.

  6. #6

    Join Date
    Jan 2019
    Posts
    320

    Re: Reciprocity Test with ND1000 Filter

    This is where Acros would shine, wouldn't it, but alas, we don't have it in sheet film (not Acros II, anyway).

    Doremus has provided great advice already. Just really note the contrast issue he mentioned. In my experience this really pushes the film when high contrast is already present in the scene. In other words, with really long exposures you either (or combine): 1) choose scenes that don't push the dynamic range of the film 2) implement development corrections, N-1, N-2, etc. 3) use grad filters to limit the contrast.

    Also note the choice of film. FP4/HP5 have lousy reciprocities once you get into a few seconds, see https://mkaz.com/film-reciprocity-tables/ :

    Indicated: 5s 10s 15s 20s 25s 30s 1m 2m 4m
    Adjusted: 13s 31s 55s 1m 23s 1m 57s 2m 35s 7m 8s 17m 21s

    Tmax is actually much better than FP4 (check it out on that site). In situations like this if the contrast is not too large (say 5-6 stops) I actually prefer shooting in color with Provia, where you don't need reciprocity corrections all the way to 4 min exposures (!), which means I can process all the sheets without adjusting development. Of course you start with a smaller dynamic range than that of B&W. And yes, it costs more. I'm not saying it's always a better way but just throwing it out. In other cases I tend to go for Tmax.

  7. #7

    Join Date
    Dec 2006
    Location
    Hamilton, Canada
    Posts
    1,726

    Re: Reciprocity Test with ND1000 Filter

    I wonder if the reliance on red light affect reciprocity as well, (separate from commonly understood filter factors) which is likely set up for white (and therefor blue) light. Silver halides are most sensitive to blue light and while this has been largely overcome since pre ortho emulsions, could very low light levels since show a bias here?

  8. #8
    Foamer
    Join Date
    Oct 2010
    Location
    South Dakota
    Posts
    2,144

    Re: Reciprocity Test with ND1000 Filter

    I successfully use +3 stops for red filters, +2 for orange.


    Kent in SD
    Qui sedes ad dexteram Patris,
    miserere nobis.

  9. #9

    Join Date
    Dec 2006
    Location
    Hamilton, Canada
    Posts
    1,726

    Re: Reciprocity Test with ND1000 Filter

    Quote Originally Posted by Two23 View Post
    I successfully use +3 stops for red filters, +2 for orange.


    Kent in SD
    In a reciprocity situation?

  10. #10

    Join Date
    Sep 1998
    Location
    Oregon now (formerly Austria)
    Posts
    2,652

    Re: Reciprocity Test with ND1000 Filter

    Quote Originally Posted by cowanw View Post
    In a reciprocity situation?
    Filter factors don't change with long exposures; you just have to figure them in before making the adjustments for reciprocity failure.

    @OP,
    B+W lists the number 90 red filter as having a factor of 5, which is 2 1/3 stops... However, they also list its Wratten number as 25. A Wratten #25 filter has a factor of 8, i.e., 3 stops. You'll have to test to see which works best for you (I use 8 as the factor with mine).

    It seems like you've found an error in your Excel formula that may help, but do make another spreadsheet with the factor Ilford gives in the document I linked to above if you haven't already; the results may be slightly different.

    Best,

    Doremus

Similar Threads

  1. Exposure correction for bellows, filter, reciprocity
    By Laszlo in forum Darkroom: Film, Processing & Printing
    Replies: 3
    Last Post: 31-Mar-2007, 17:34
  2. hp 5 reciprocity
    By scott palmer in forum Darkroom: Film, Processing & Printing
    Replies: 12
    Last Post: 14-Dec-2004, 09:07
  3. Efke 25 4x5, Reciprocity Compensation Test
    By Andrew O'Neill in forum Darkroom: Film, Processing & Printing
    Replies: 7
    Last Post: 22-Jun-2004, 10:53
  4. Hitech ND Grad filter test images
    By bmgmusic in forum Lenses & Lens Accessories
    Replies: 1
    Last Post: 30-Dec-2000, 18:44

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
  •