Will This Idea Work?

[dennis_oconnor5]

<p>Hello everyone. This is a question about calculating film speed using a home made step wedge.</p>

<p>I very carefully made an 8" x 10" 21 segment step wedge (1/3rd stop) in my darkroom using my enlarger without any filtration or negative in the carrier. I first made some test exposures to establish Dmin. This exposure I use as my starting point. Each segment was exposed using separate exposures for the time required (not multiple exposures). I printed the step wedge on a grade 2 matt finish paper.</p>

<p>When the print had dried I mounted it and photographed it. The exposure was calculated using a pentax spotmeter and kodak grey card. I then exposed the film at a range of ASA speeds. I processed the film, Fomapan 400, in Parodinal 1:50 for 11 mins at 20 deg C.</p>

<p>I printed the negatives on to grade 2 paper. My idea was to spotmeter the grey card in the stepwedge position and get a reading. I then took spotmeter readings from the segments of the step wedge to establish which segment number corresponded to the grey card reading, e.g. segment 10.</p>

<p>I then used the same procedure on each of the final prints to see which segment 10 gave me the same reading. Each print had the exposure details on the back. I found that the print that gave me closest reading (segment 9) was exposed a +2/3 stop (250 ASA). This corresponds to a loss of film speed with this developer that I have read in this forum.</p>

<p>What I would like to know is. Does this seem like a useful method and procedure or have I missed something?</p>

<p>Thanks for any advice.</p>

[dennis_oconnor5]

<p>Edit. Delete (segment 9). Read (segment 10).</p>

[dennis_oconnor5]

<p>I have been thinking about this idea (I know that can be dangerous). If I were to make only one print of the step wedge with a negative exposed at the manufacturers ASA speed. Spotmeter the grey card and establish which of the segments on the step wedge matches that value. On the print of the negative. Locate the segment that gives the same value. If the segment numbers are the same, then the film speed would be as stated by the manufacturer. But. If the matching segment were for example 2 numbers lower would that not indicate a speed lower by 2/3 of a stop.</p>

<p>Example. Step wedge segment number = 12. Print segment number = 10. This would equal a speed lower by 2/3 stop.</p>

<p>All donations gratefully received.</p>

[conrad_hoffman]

<p>Thinking has certainly gotten me in trouble over the years, but what you really care about in determining film speed is the shadow area. Nothing else matters because that will be adjusted in development and printing. It's for this reason people worry about "0.xx over base plus fog". I think .xx is usually .1 but it's been a while. I'd suggest doing the standard Zone System film speed test (or just forget the whole thing and use 50-100% of the ISO speed because that's the result almost everybody gets anyway). Once you have the film speed pinned down, use the step tablet to determine the development necessary to print on #2 paper (IMO, #3 is a better choice for 35mm negs).</p>

<p>CH</p>

 

[Bob K]

<p>I agree with Dennis and Conrad on the possible methods that you might use. I guess my question to you is why are you going to all this effort? I would sugguest a that you take a roll ,of whatever film that concerns you, use an incident meter and do a 5 stop exposure series. Process at recommended times and then print your results with standard times and temps. What works for you is what works. I am assuming that you have you printing workflow standardized to your needs.</p>

<p>Conrad is correct that the ISO range will be 50-100%. Hmm, big range, try the above with a specific camera, metering method. Hold the darkroom processes constant.</p>

<p>Conrad, no put down intended, but equipment and film must be calibrated together.</p>

<p>Bob</p>