Paddy said:Todd, maybe you could provide a brief review of the methodology for your test.
i.e. Were you inside using 2 blue Photofloods or tungstens, w/ grey card, w/lights at 45deg. angles as in copy art set-up?
Or,... were you outdoors on sunny day, 12 noon, facing north side of building, very open shadow, w/ grey card or even surface?
Did you stop down 4 stops from indicated meter reading to get your Zone I?
What were your actual density readings?
Just asking, so that we can understand your path to results.
Donald Miller said:How did you do this testing? Did you have the lenses focused at infinity? Did you photograph a evenly colored textureless surface? How did you define the EI test exposure?
Todd Barlow said:- I photographed a 20 by 24 dark blue sheet of bristol board
Donald Miller said:quote:
"- metered the card picked 1/125 as shutter speed and closed lens 6 stops (to give Zone 1 less 2 stops) exposed and then opened up lens in 1/2 stop increments until I was at Zone 1 plus 2 stops
- Density readings for the 80mm lens are shown below
- Zone V meter reading 1/125 f between 2.8-4
- 1/125 f between 22-32 density .06 (Zone 1 less 2 stops = EI 1600)
- 1/125 f 22 density .10 (Zone 1 less 1 1/2 stops = EI 1200)
- 1/125 f between 16-22 density .18 (Zone 1 less 1 stop = EI 800)
- 1/125 f 16 density .24 (Zone 1 less 1/2 stop = EI 600)"
My response:
O.K. if you are using a Pentax spot meter the Zone V should be a lot more defined then 1/125 between 2.8 and 4. That is a whole stop of variation and your spot meter will give you 1/3 stop readings.
So if we assume that your meter indicated F4 then if you closed the lens down by seven stops as you indicated then that would be F 32 at 1/250 second not F 32 at 1/125 second. You have made a one stop miscalculation in that result.
It might prove beneficial to review your calculations and use your meter to determine the correct Zone V exposure down to the 1/3 stop (it is capable of more precision then one stop variance) that it is capable of showing you and then make the correct calculations.
blaughn said:Todd-
From metered setting, you need close down 4 stops to give you a Zone I
Secondly, a leaf shutter at 125th with lens aperatures of f16 or smaller will cause a 1/3 stop over exposure. I think you have a couple of things working against you here.
Are you explosing the rest of the roll at Zone VI?
Kirk Keyes said:I would suggest that your dark blue board is not close to Zone V. That's why you have the weird film speeds.
You should get a grey board that meters as close to a 18% grey card as possible and try your tests using the grey board as your target.
Kirk - www.keyesphoto.com
blaughn said:Todd:
At what ASA was your meter set?
Todd Barlow said:[...] I had read that the actual colour was not important as long as it was evening lit and was even in texture and colour since the meter would provide an exposure that would result in a Zone V exposure.
Paddy said:Kirk, I don't think that the colour of the board has anything to do with the meter readings, other than to influence one's choice of exposures. Everything a meter is pointed at is 18% grey, as far as the meter is concerned.
nworth said:I'm having a hard time interpreting your density values. They do not appear to be conventional density measurements.
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