Trying to figure out exposure for Stouffer TP120-31

qualsound · Dec 16, 2013

Bill Burk said:
It's better science to eliminate variables from testing. Flare is a variable that can easily be eliminated from the experiment by placing the Stouffer scale in contact. But I didn't come here to harp on that.

Bill!
i tried to follow your advice and take a photgraph of the stouffer by putting it right before the film plane into the filmback. i used a 150mm lens focused at infinity...
into the filter holder of the kompendium i slid a transparent piece of paper (used for graphic illustrations, etc.) exposing the film during yesterdays cloudy sky 5 stops more than the lightmeter suggested. i developed for 5,5 minutes.

Please check the results,...i don't know what happened...it look like i got so much flare...or is it a light leak inside the filmback/camera???
because even the unexposed but developed part of the film has a density of 0.15
...considering that it could be that around 1/2 stop of fogging caused by a lightleak (or whatever??) damaged and will be damaging all of my filmtests...
please correct me if i am wrong: measuring step nr. 1 on the original stouffer tablet is 0.06 + 0.15 flare/lightleak/whatever equals 0.21!!! so around the actual 0.22 (step 31) of yesterday's contacted stouffer on the hp5.

i am pretty confused...

Bill Burk · Dec 16, 2013

0.15 B+F is not unusual. Could be light leak "due to handling". But it is something you could improve if that's the case.

The 5.5 minute test is overexposed, because you didn't "capture the toe" but notice how the curve continues all the way into your steps 20-30. Your other tests in the screenshot were camera tests and they are flat after step 20... The continuation of the curve in all steps of the test are what makes it clear to me that you made a contact exposure for the 5.5 minute test.

qualsound · Dec 16, 2013

Bill Burk said:
0.15 B+F is not unusual. Could be light leak "due to handling". But it is something you could improve if that's the case.

The 5.5 minute test is overexposed, because you didn't "capture the toe" but notice how the curve continues all the way into your steps 20-30. Your other tests in the screenshot were camera tests and they are flat after step 20... The continuation of the curve in all steps of the test are what makes it clear to me that you made a contact exposure for the 5.5 minute test.

Bill, the other tests shown in the spreadsheet are the ones, you charted on paper and were, like you said, 4 stops underexposed...i only replaced the 5.5 minute test with the densities i measured yesterday in the data sheet.
i did the test from yesterday like Michael (there was a url link here which no longer exists) because he got good results with that...at least what i can read out of his posts in this thread (there was a url link here which no longer exists)

Bill, what are you suggesting? to do the test (by contacting) the same as i did yesterday,...but use only a 3 stop overexposure on the lightmeter?

----------------------

regarding densities...Ralph suggests to take absolute density readings...so to null the densitometer when there is nothing in the light path...so i did it that way measuring all the densities on the stouffer

or

is it better to take relative readings...nulling the densitometer to an unexposed piece (=B+F?) of the tested film and then read all the densities relative to that first null measurement...is that a reading relative to base and fog (so b+f is subtracted from the measurements)...?

Bill Burk · Dec 16, 2013

qualsound said:
Bill, what are you suggesting? to do the test (by contacting) the same as i did yesterday,...but use only a 3 stop overexposure on the lightmeter?

Yes, you overexposed according to the lightmeter by 5 stops, and you are about 2 stops from reaching under 0.10 density in your results. So a 3 stop overexposure according to the lightmeter will get you the 2 stops you need to reach the toe.

Don't worry about whether you zero on clear air or B+F. As long as you keep the information (for example noting B+F in your records), the math to convert from one method to the other is "addition".

qualsound · Dec 17, 2013

Bill Burk said:
Yes, you overexposed according to the lightmeter by 5 stops, and you are about 2 stops from reaching under 0.10 density in your results.

Bill, one question arises then...look at the densities from the test i did underexposing the films by 4 stops...how is it possible that i can not get under 0.10 density even at 4 minutes dev. time (0.12 and even 0.19 at 16 min. at step 31 on the stouffer) even if the film is underexposed by 4 stops...?
Are you saying that these "low" densities from 0.12 up to 0.19 are caused by flare photographing the stouffer off of a window (that is the way i did it for my first try on film-testing)...?

qualsound · Dec 23, 2013

bill or anyone else can help? highly appreciated!

richard ide · Dec 23, 2013

Film base plus fog. Why would you want to get a density below .10. It is totally unnecessary. High contrast graphic arts films will do it, but not suitable for general pictorial work.

qualsound · Dec 23, 2013

Richard...is a density for b+f of 0.12 "normal" for a hp5+ developed for 5.5 minutes in ID-11 1:1....???

richard ide · Dec 23, 2013

Your b+f density will vary depending on all the variables which occur related to exposing and processing that piece of film. It is similar to an all over neutral density filter and when you make a print you burn through it. With your example, your density is pretty close to ideal.

qualsound · Dec 24, 2013

thank you for your answer, Richard!

Bill Burk · Dec 24, 2013

Hi qualsound,

Sorry I didn't see your question until now, fell off the APUG My Posts screen somehow...

Richard is right, the reason your earlier 4-stops-underexposed tests never reached zero is that you have Base+Fog included in the density you plotted. I prefer to take out Base+Fog from my graphs but do not want to contradict Ralph Lambrecht who prefers to keep these values embedded. It's his spreadsheet so keep it that way, but that's why your curves do not touch zero.

qualsound · Dec 24, 2013

nevermind bill! thank you for clarifying...i just wanted to be sure that 0.12 for 5.5 minutes in ID-11 1:1 is kind of a "normal" B+F density for a hp5...
..knowing that i can hopefully carry on my film-tests...

Bill Burk · Dec 24, 2013

You can fix/wash/dry a piece of film to separate Base from Fog. 0.12 is reasonable Base+Fog for any process. You can probably find base density in the specifications or ask Ilford. 35mm often has a gray base to improve antihalation. 120 and sheet film is usually clear, but even "clear" often measures about 0.05 on my densitometer. (That would mean your Fog might be 0.07 which isn't awful).

Trying to figure out exposure for Stouffer TP120-31

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