Is this OK, enlarging exposure meters calibration

[haris]

Hello,

When calibrating enlarging exposure meters, as you know, exposure time is calibrated/metered on lightest part of projected negative (darkest part of "real life situation" image) which still have details wanted to be seen on print, and contrast on darkest part of projected negative.

So, instead of using some random negative to calibrate meter, it would be nice to have dedicated negative as calibrating device. My question is:

If I make photograph of, for example, white T-shirt and black T-shirt, one next to another, under diffused light (let say light through room window) can that be used as calibration "template". Is contrast range in that case too big? Is white T-shirt too light for calibration or black T-shirt too dark?

What would you consider as "lightest" and "darkest" tones which will be suitable to calibrate those meters?

Thank you

 

[Donald Miller]

That would depend on the degree of development of the negative. You could vary the density range by quite a bit depending of course on the film, developer, and agitation. Since most exposure meters are measuring light at the baseboard, density of the negative and hence the density range, as in the example that you mentioned, does vary the light intensity at that point.

Furthermore your negative, once calibrated to a given paper grade, would only be valid at that paper grade from the same paper mfg.

This would be a workable system provided you decide what you want at a given tonal range...does your white go paper base white or does it show some texture...in the case of the white teeshirt. For the same matter is your black tone at dmax or does it exhibit some tonal evidence? These are questions that only you can answer for yourself when you go about calibrating your meter.

Your thoughts about the extremes of the tonal scale is valid and the ones that I would choose...stay away from 18% gray...zone V or any of the other middle tones...they are not what you want in this case. If the ends of the tonal scale are determined and fixed then the middle zones will fall where they will.

 

[Daniel_OB]

I use a meter in darkroom only as a giude. I made a strip with different exposure, changing only apeerture) and measure apperture with a meter for each one. Develop the strip by standard time. Now for enlarging I measure the light with my meter (time set the same as for test) below specific area on the negative and find the same apperture on my strip, and that is the tone how that specific area from the negative will appear on the final print. You have to use meter always at the same point on the easel and move negative to measure from different areas.
I use minolta flashmeter V for it.

www.Leica-R.com

 

[Roger Hicks]

White and black T-shirts are probably ideal; or for a bit more range, try white T-shirt and black velevet.

Either will get you a good work print, from which you modify your print exposure in the light of subsequent readings.

The real question is 'single lighting' (everything evenly illuminated) versus 'double lighting' (some of the dark areas in shadow of varying intensity). Take a look at
http://www.rogerandfrances.com/photoschool/ps subject brightness range.html

 

[haris]

Thank you all for answers,

I wanted in this case both T-shirts, white and black, to show details, that is fabrics of which T-shirts are made to be visible. I assume that would be range between lightest and darkest, both containing details, that in most situations is needed, and lighter or darker than that in "normal" situations would lost details.

Donald, in this case white T-shirt it was paper base white, but I made error when processed film, didn't cool down chemical temperatures, so temperature of chemistry was 35 to 40 Celsious!. I will make anoother "test negative(s)", this time properly processed , but in meantime I wanted to ask people who know better than me those things, am I on right track.

Roger, I assumed velvet would be "too dark", like one zone darker than black T-shirt, that is not absolutely black, but still black without details, but will try velvet too. And thank you for link.

So, I guess from yours answer(s) T-shirts would be way to go.

 

[Roger Hicks]

So, I guess from yours answer(s) T-shirts would be way to go.

Dear Haris,

Yes, subject to 'double lighting'; you are quite right about black velvet under uniform lighting.

Cheers,

Roger

 

[haris]

Dear Roger,

Thank you very much.