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Old 31st January 2010, 04:10 PM
Tony Marlow Tony Marlow is offline
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Default Film testing, filter factors Prescysol

Hello Les,
I understand the importance of film testing which is done without using filters but invariably filters are often used and exposure allowance must be made. I have cameras with TTL metering and a separate spot meter. With say an B+W yellow/orange filter the filter factor is 4 ie plus 2 stops but when measuring the with a meter the difference is only one stop. Using the wrong factor makes an exposure error of one stop which negates the work done in film testing. Do you use the manufactures filter factors to adjust exposure or use the value metered through the actual filter.
Another point on film testing; with Prescysol Peter Hogan says there is little effect on development by changing the time so there is little point in testing for development times when establishing your own film speed. Peter says that the only thing you can do is to increase the strength of the dilution which increases the contrast. So when checking your own film speed with Prescysol do you stick with standard dilution and times for all the exposures or how do you vary the development to determine your N+, N- etc?
Tony
 
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Old 31st January 2010, 04:54 PM
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Les McLean Les McLean is offline
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Quote:
Originally Posted by Tony Marlow View Post
Hello Les,
I understand the importance of film testing which is done without using filters but invariably filters are often used and exposure allowance must be made. I have cameras with TTL metering and a separate spot meter. With say an B+W yellow/orange filter the filter factor is 4 ie plus 2 stops but when measuring the with a meter the difference is only one stop. Using the wrong factor makes an exposure error of one stop which negates the work done in film testing. Do you use the manufactures filter factors to adjust exposure or use the value metered through the actual filter.
Another point on film testing; with Prescysol Peter Hogan says there is little effect on development by changing the time so there is little point in testing for development times when establishing your own film speed. Peter says that the only thing you can do is to increase the strength of the dilution which increases the contrast. So when checking your own film speed with Prescysol do you stick with standard dilution and times for all the exposures or how do you vary the development to determine your N+, N- etc?
Tony
Tony, I carry out a series of tests to determine the filter factor that suits me given that I prefer a somewhat "meaty" negative. I select a subject where the filter being tested will have an effect and start by making what I deem to be the correct exposure without using a filter. This is to establish the exposure that will give me the detail and density I require, in effect it is a "reference" exposure. I then make exposures using the filter and start at one stop less and go up to 2 stops beyond than exposure suggested by the manufacturer. The negative that is nearest the "reference" exposure in density and detail is the factor that I apply thereafter. The major difference between the two negatives will probably be a change in contrast on the filtered exposure.

Your question on Prescysol is interesting for having spent a photographic lifetime manipulating development to adjust negative contrast I did have difficulty in accepting Peter's suggestions relating to contrast control. Initially, I used the suggested dilutions but was unhappy with the density of the negatives so I doubled the strength of part B. I use EF and Peter's suggested dilution is 1 part A 1 Part B to 100 parts water, I use 1 part A to 2 parts B to 100 parts water. I also use the partial stand time of 10.5 minutes and this gives me the density that I prefer in my negatives. Having said that, even though Prescysol used as per Peter's suggestion produces "thinner" negatives there is still a lot of information and detail there.

With regard to controlling Normal, Plus and Minus development, I have to say that since I started to use Precsysol and EF I have never felt the need to manipulate my negatives in the manner that I had done up to that point in my photographic life. I tested Prescysol for Black and White Photography many years ago and frankly, did not believe Peter's claims when he sent me that product for the test. I compared Precsysol with PMK and Rodinal using FP4 exposed on a subject that had 7 stops of contrast (a beach scene on a bright sunny day). I exposed three rolls of film in identical conditions and devleloped them in the three developers listed above. Rodinal was very poor because of the contrast, which I expected, PMK was better but still difficult to print, Precsysol printed straight with detail throughout. I made all three prints on grade 2 paper so that the only difference was the negative developer. I have used Precsysol since that day and aplogised to Peter face to face for doubting his claims.
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Old 31st January 2010, 06:15 PM
Tony Marlow Tony Marlow is offline
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Thanks Les that was most helpful. You have removed a niggle I have had for a long time about film speed testing with Prescysol. It seems that Prescysol removes one variable in the procedures and that simplifies the film speed testing. We will just have to make sure Peter keeps going for a long time with his secret formula!
Many thanks,
Tony
 
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