Overexpose in harsh lighting?

[andy_laycock1]

I thought I would take advantage of the great expertise in this forum to ask what might be a dumb question. I was shooting in an urban environment with another photographer on a very bright and harsh day. He said in that situation he overexposes his 400 film by one stop and underdevelops. I understand the underdeveloping part but I'm not sure of why you would overexpose in this situation (assuming the meter and your judgement are correct).

[alan_gibson6]

It has been said "there are no dumb questions, only dumb answers", so

here comes one.

 

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He does this because he is a zone system fanatic. Or, at least, he

knows some of the underlying principles.

 

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His subject is contrasty. He knows that a normal exposure and

development will yield a negative that is also contrasty, and will be

difficult to print. So he plans on developing less. This will reduce

the contrast on the negative: subject highlights that would have been

a dense black will be, say, a dark grey. But it also affects, to a

lesser extent, the other end of the characteristic curve: shadows

that would have been light grey will be slightly lighter, or totally

clear. By giving the extra exposure, he knows that he can raise the

tone of the shadows back where they would have been with normal

development.

 

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The opposite also applies: increasing development ("pushing" the

film) gives increased contrast as well as requiring less exposure

(increasing the EI).

 

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Of course, he has read Adams and BTZS, and has done extensive

testing, and knows how to adjust EI (Exposure Index) and development

to give a required CI (Contrast Index), while retaining Zone 0 at

density 0.1 above film-base-plus-fog.

 

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On the other hand, perhaps he just knows a couple of rules of thumb.

[sergio_ortega]

Andy, the basic "rule of thumb" Alan mentions, and the one you may wish to remember, is: Expose for the low values, Develop for the high values. This is the basic concept of the zone system.

 

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Exposure/density in the low values/zones is determined by the chosen film EI. Choose a lower EI and you have increased exposure/density in the low values/zones; choose a higher EI and you have decreased exposure/density in the low values/zones. Density in the low values/zones is determined more by initial exposure than by subsequent film development.

 

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Density in the high values/zones is determined more by development times/temperature/dilution than by the EI chosen. Develop for longer times/at higher temps/in stronger dilutions and you increase density in the higher values/zones at....and this is key!....a greater rate than in the lower values. Develop less, and the opposite is the case.

 

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Sergio.

[alan_gibson6]

Sergio puts it well. Although the "overexposed" highlights will be

denser, this will be more than compensated for by the

"underdevelopment".

[mike_rosenlof2]

The zone system rule in a nutshell is (as mentioned) "expose for the

shadows, develop for the hilights".

 

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The _reason_ for this is (with negative film) you don't want to

underexpose, and you don't want to overdevelop. So if you've added

exposure to get shadow detail, if the hilights are very bright, you

need to reduce development to not overdevelop those areas and block up

all off the hilight areas.

 

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These are the ideas behind the zone system. Now you can pile on all

of the calibration and testing to very precisely set your film speeds

and development times...