Author Topic: Nikon F2a green sensitivity of cds cells  (Read 229 times)

hkoepke

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Nikon F2a green sensitivity of cds cells
« on: July 28, 2021, 16:57:41 »
I noticed that negatives from photos I took in the park with a lot of green in the picture turned out to be very thin.
I started to compare my exposure meters of my F3 HP, F5, F2AS and F2A.
The result was, on neutral motives they were all pretty close within +/- 0.5 f-stop. This was valid for dimmer as also for brighter motives.
But – The big difference came when I checked on motives with a lot of leaf green. The cds cells from my F2A showed 1 f-stop more light, than all other cameras I compared to. So the result would have been a 1 f-stop underexposure. I have to add, my F2a was serviced by Sover Wong three years ago, he also exchanged the old cds cell to new ones. It came back like new.
Have you had similar experiences with cds cell meters like in the Nikon F2a?

Best regards Henning


Wannabebetter

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Re: Nikon F2a green sensitivity of cds cells
« Reply #1 on: August 09, 2021, 12:06:20 »
Have you had similar experiences with cds cell meters like in the Nikon F2a?
Best regards Henning

In answer to your question, no. Did you control for film stock, batch consistency etc? Where was, or by whom, your film processed? You mentioned that Mr. Wong fairly recently serviced your F2a. Do you know where he sourced the "new[?]" cds cells? (I do know that, in fact, he cannibalizes old bodies for spares.) What was the condition and/or service history of your other cameras?

I'm no expert on the venerable F2a, my own experience not exceeding my successfully removing a severely damaged mirror box for a better, used, one. (Well, actually, I have messed a bit with -- or messed up! -- a couple of iterations of F2 viewfinders in an attempt at cleaning them or tapping out the odd dent or bend in the housing. But no calibrations etc, were attempted.) Moreover, I was shooting primarily in black-and-white at that late stage in film-camera development -- no pun intended -- and have been shooting digital exclusively since purchasing a used D100 fifteen or more years ago. So I won't be much, if any, help to you in these regards. Still, I just had to ask those questions.

David H. Hartman

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Re: Nikon F2a green sensitivity of cds cells
« Reply #2 on: August 09, 2021, 19:01:56 »
There are several possible problems with a CDs meter. One is they have a memory for bright light. If exposed to direct sunlight the memory might last for 30 minutes, a day or even destroy the metering cells.

Variations in color sensitivity is a known problem with light meters. I remember a company that would calibrate the popular Pentax Digital Spotmeter for metering accuracy with pure color subjects.

Black and white films are quite sensitive to blue light so using a yellow, orange or red filter can easily cause under exposure in open shade even with monochromatic subjects. The filter factors published for B&W filters were for a daylight color temperature of about 5300K. A grater filter factor is needed for the blue light of open shade.

Blue filters and intensely blue light will darken not only warm colors but also green and a green filter will darken blue. I don't think many know this. The blue light of open shade may cause under exposure of dark green foliage. Deep blue and green color separation filter can be used to advantage where one may wish to differentiate between blue and green in a subject when shooting B&W. 

I once read that giving B&W film an extra stop of exposure was, "...about as dangerous as taking extra sandwiches to a picnic." I recommend rating B&W negative films with an EI of one stop less than their ISO and under developing slightly (pull process). It is inherent vice that shadow detail that can be seen in a negative may be so thin as to be unprintable. I rated Kodak's Tri-X at EI 200 and Ilford's HP5 the same.

If bracketing B&W film I would only give a second exposure with one extra stop. Bracketing one stop under would almost always give thin negatives that were less than ideal. When using a deep red filter with B&W film several extra stops may be needed to properly record shadow detail in open shade.

There are a lot of factors to consider beyond the potential color sensitivity of CDs meter cells.

Dave
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