Reciprocity for Adox CMS 20 II

[jamgolf]

@Adox
@ADOX Fotoimpex
@Team ADOX

The datasheet for CMS 20 II says the following:

Reciprocity failure factors:
Between 1/1000 und 1/10s the film can be exposed at regular speed
At 1 second add + 1/2 Stop
At 1/1000 seconds add + 1/2 Stop

But ^ this is not clear to me.

Can you please provide correct compensation for the following scenarios?

1. If the calculated exposure is 0.5 seconds then what is the compensation for reciprocity? and the correct final exposure?
2. if the calculated exposure is 1.5 seconds then what is the compensation for reciprocity? and the correct final exposure?
3. If the calculated exposure is 6 seconds then what is the compensation for reciprocity? and the correct final exposure?
4. If the calculated exposure is 11 seconds then what is the compensation for reciprocity? and the correct final exposure?

Thanks very much for your help!

 

[Donald Qualls]

If the calculated exposure is 0.5 seconds, half a stop compensation. If it's 1.5, you'd need to add at least a half stop (film manufacturers always say to open the aperture, but if you could do that, you likely wouldn't be shooting at that speed). It's very probable you actually need more than a half stop addition for longer exposures like 6 and 11 seconds, because reciprocity failure isn't a simple loss of speed -- it's more loss of speed the lower the light intensity (= the longer the metered exposure). It should be possible to back out the Haist exponent (you'd raise the number of stops above 1/10 second to this power to get your actual exposure time), but that might require they give more levels of compensation.

Without more information, I'd have to suggest shooting a test, half a roll or so, at a light level and aperture that calculates to one second -- and shoot at metered time, plus 1/2, plus 1, and plus 2 stops to see which works best. Then do the same at, say, 4 seconds metered exposure.

 

[jamgolf]

Thanks @Donald Qualls
What you say about testing is probably the way to find out but the manufacturer should provide clearer guidance and there should not be a need for any experiments.
Ilford provides simple factors for each film. I think it would be very nice if Adox provided similar factors:

 

[Donald Qualls]

Those are the exact Haist exponents I was referring to. None of those films need compensation below 1 second, however; CMS 20 apparently needs it from 1/10. If we presume a 1.3 exponent starting from 1/10 (a pretty reasonable figure for films that aren't Acros or Foma) we'd (10^1.3)/10, which is about 2 seconds when the meter reads 1 second, and (50^1.3)/10 = ~16.2 sec for a metered 5 seconds, and so on. Given they want a half stop at one second, that's an exponent of more like 1.2.

Tempting to suggest an EI of 20 isn't intended as an invitation to shoot in low light, but a half roll test will tell you everything you need to know.

 

[jamgolf]

.. but a half roll test will tell you everything you need to know.

Thanks again. Unfortunately, I only have 4x5 and 8x10 cameras at the moment. But that would be the way to find out.
Maybe someone else has done this experiment already and can share their findings

 

[JensH]

Thanks @Donald Qualls
What you say about testing is probably the way to find out but the manufacturer should provide clearer guidance and there should not be a need for any experiments.
Ilford provides simple factors for each film. I think it would be very nice if Adox provided similar factors:

Hi,

to use these P values the adjusted time is calculated this way:
Ta = TmP
with
Ta = Adjusted Time
Tm = Measured Time (from Ilford's data sheets)

Best
Jens

 

[Raghu Kuvempunagar]

None of those films need compensation below 1 second, however; CMS 20 apparently needs it from 1/10.

At what EI? If CMS 20ii is shot at EI 6 does the exposure needs to be compensated at 1/10? Note that 6 is arguably the sweet spot for this film as it requires temperature juggling with Adotec developer and the use of fill flash to get the best results at higher speeds.

By what factor should the development be shortened when reciprocity corrections are used?

 

[Donald Qualls]

to use these P values the adjusted time is calculated this way:
Ta = TmP
with
Ta = Adjusted Time
Tm = Measured Time (from Ilford's data sheets)

This requires some adjustment, however, for films that need correction at times shorter than 1 second. As I gave in my example, you have to multiply your metered time by (in this case) 10, to get the number of 1/10 second increments, apply the exponent, and then divide the result by ten (because you've gotten a result in tenths of a second).

At what EI? If CMS 20ii is shot at EI 6 does the exposure needs to be compensated at 1/10? Note that 6 is arguably the sweet spot for this film as it requires temperature juggling with Adotec developer and the use of fill flash to get the best results at higher speeds.

By what factor should the development be shortened when reciprocity corrections are used?

The compensation factor given is for box speed in the recommended developer (there's a special formula for this microfilm derived stock, as I recall). If you're exposing more, in theory you could compensate less -- I'd use the same exponent but start at a longer exposure, in the case of 1 2/3 stop, perhaps 1/2 second instead of 1/10. In practice, however, you're stepping into even more uncharted territory by using a personal EI and then shooting outside the reciprocity range. Once again, testing is required to be sure.

 

[jamgolf]

I was looking at the datasheet for Adox CHS 100 II and very clear guidance is provided by Adox. Nice job Adox!

The same kind of simple/clear guidance should be provided for Adox CMS 20 II as well.
@Adox @ADOX Fotoimpex @Team ADOX

 

[Donald Qualls]

I agree -- that's plenty of data to calculate a Haist exponent. Looks like 1.46, near enough.

 

[Andrew O'Neill]

I haven't done extensive testing like I usually do, but this data seems to give me decent results. I've not adjusted development times.

1 sec give 1/3
2 sec give 1/3
4 sec give 2/3 or 1.5X
8 sec give 1 stop or 2X
15 sec give 1 1/3rd stop or 2.5X
32 sec give 1 2/3rd stop or 3X
64 sec give 2 stops or 4X

 

[jamgolf]

Thanks for sharing your data @Andrew O'Neill

 

[alanrockwood]

I was looking at the datasheet for Adox CHS 100 II and very clear guidance is provided by Adox. Nice job Adox!

The same kind of simple/clear guidance should be provided for Adox CMS 20 II as well.
@Adox @ADOX Fotoimpex @Team ADOX

I just did some reciprocity testing for Fomapan 200 (used at a personal exposure index of 100), and I get almost the same numbers as the ones you posted for Adox CHS 100 II.

 

[alanrockwood]

I agree -- that's plenty of data to calculate a Haist exponent. Looks like 1.46, near enough.

Here's another function that fits the Adox CHS 100 II data quite well. The equation is given in

the attached figure. I used an equation similar to one that Gainer used, except that the exponent was a variable parameter (which optimized to 1.66) rather than being a constant as used by Gainer (1.62). I optimized both the factor (0.35) and the exponent (1.66) to fit the data.

 

[K-G]

Here's another function that fits the Adox CHS 100 II data quite well. The equation is given inView attachment 278438 the attached figure. I used an equation similar to one that Gainer used, except that the exponent was a variable parameter (which optimized to 1.66) rather than being a constant as used by Gainer (1.62). I optimized both the factor (0.35) and the exponent (1.66) to fit the data.

Thank you for sharing. Very useful .

Karl-Gustaf

 

[Craig75]

I would have thought that between 1/10th and 1 second getting anything accurate at under 1/2 stop extra compensation isnt really realistic especially with large format shutter

 

[jamgolf]

I agree -- that's plenty of data to calculate a Haist exponent. Looks like 1.46, near enough.

Thanks @Donald Qualls
I've got a box of CMS 20 and will try using this exponent of 1.46 for reciprocity compensation. Wish me luck

 

[Team ADOX]

I was looking at the datasheet for Adox CHS 100 II and very clear guidance is provided by Adox. Nice job Adox!

The same kind of simple/clear guidance should be provided for Adox CMS 20 II as well.
@Adox @ADOX Fotoimpex @Team ADOX

We will try to do those detailed test runs as well for ADOX CMS 20 II.
But please have some patience, as our experts for that are currently working on much more important projects with much higher priority. Please don't forget that our resources are quite limited, as we are a very small company. And despite the fortunate fact that the pandemic has not had any negative influence on film demand so far (just the opposite), the pandemic had and still has many negative impacts for manufacturers on the supply side. These negative impacts have hit several of our projects quite hard.
Thanks for your understanding.

ADOX - Innovation in Analog Photography.

THE BEST THINGS IN LIFE ARE ANALOG.

 

[Donald Qualls]

This kind of testing shouldn't be particularly difficult for an end user who has a well controlled development process (using a suitable developer in the case of CMS 20 II) and the equipment to do sensitometry. I'd bet @Greg Davis aka The Naked Photographer could do it, for instance (if he has time, of course, between earning a living and making those excellent videos).

Unless I'm missing something major, it's mainly a matter of first establishing a base film speed, then retesting speed with lower and lower illumination (= longer and longer exposure times) to establish how much speed is lost as the calculated time extends. Might take more than one 35mm roll, but it might not.

 

[Andrew O'Neill]

I do my testing under an enlarger with a 10x and 100x ND filters, and Stoeffer 31 step, step wedge. The filters are so that the aperture stays constant. 60th sec, 1 sec, 10, and 100 sec exposures are given. Film is developed, then densities read and graphed. Speed losses for slower speeds can be compared to 60th sec curve. Data is then tested in the field. This has worked for me for many years.

 

[Donald Qualls]

I do my testing under an enlarger with a 10x and 100x ND filters, and Stoeffer 32 step, step wedge. The filters are so that the aperture stays constant. 60th sec, 1 sec, 10, and 100 sec exposures are given. Film is developed, then densities read and graphed. Speed losses for slower speeds can be compared to 60th sec curve. Data is then tested in the field. This has worked for me for many years.

And there we are. Could get three repeats of this on a single roll, with a little care, unless that step wedge is longer than I think it is.

 

[fs999]

Why Agfa-Gevaert didn't that chart ? Perhaps there is a chart somewhere... The film is now branded EPM ImageLink HD.

 

[Sal Santamaura]

We will try to do those detailed test runs as well for ADOX CMS 20 II...

Now 16 months later, have you had an opportunity to run the reciprocity tests yet? Thanks in advance.

 

[Sal Santamaura]

This might be of limited value to those working in very low light and/or with view cameras, especially since Mirko recently announced that there will only be a couple more years' worth of CMS 20 II, but I just evaluated my reciprocity test results from six weeks ago. I'm only using 35mm, outdoors with average to low-intensity daylight conditions. I exposed a roll of CMS 20 II, calibrating density to Zone V, at decreasing shutter speeds, with "brackets" at longer exposures after each step. Film exposed at EI 6 and developed in Adotech IV for eight minutes at 68 degrees F.

Result: no compensation needed until 1.5 seconds. Since aperture is critical in 35mm to maximize resolution with this film, and my earlier tests had revealed optimum as f/9.5 for the 45mm Nikon PC-E used, adjustment to correct was by extending time rather than opening the lens. That 1.5 seconds needed to become 2.0 seconds. One and a half seconds was as far as I took things, since if a scene meters longer than 1.5 seconds at f/9.5, I'm not likely to be photographing it. I hope this is useful to those who have or plan to stockpile CMS 20 II.

 

[Andrew O'Neill]

My data is as follows: at 1 second I give a third stop more. 2 seconds becomes three seconds (or 2/3rd stops), 4 seconds becomes 6 seconds...