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Incident Light metering


Stealth3kpl

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I would not mention this, but someone has mentioned Weston meters. If one is lucky enough to have an old one, then compare it to a more recent one. They are definitely calibrated differently. They changed after model III.

 

When I worked at the school of art & design we had about two dozen Westons, IV, V, and Euromaster, and at one time I actually owned three, 2 IVs and a Euromaster. It was rare to find two that read the same but differences were minor. Believe me this is not untypical, the cells, wether selenium ir cds etc are not that cinsistent or linear.

 

Its an art, get used to one and don't look too closely at comparisons!

 

Gerry

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Hi

 

Correct the Westons were made over 60 years.

Early ones were calibrated in Weston rather than ISO, 1/3 of a stop difference, it says Weston on the meter..

Then they made the cell bigger for additional sensitivity, which altered the angle of acceptance, a difference in reflected mode.

They changed the incident attachment.

I've only got three that still work, II, III & V, and they are all within 1/3 of a stop of each other. They are calibrated for zone use, discretely... suuuush

 

Noel

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Hi

 

Correct the Westons were made over 60 years.

Early ones were calibrated in Weston rather than ISO, 1/3 of a stop difference, it says Weston on the meter..

Then they made the cell bigger for additional sensitivity, which altered the angle of acceptance, a difference in reflected mode.

They changed the incident attachment.

I've only got three that still work, II, III & V, and they are all within 1/3 of a stop of each other. They are calibrated for zone use, discretely... suuuush

 

Noel

 

I am pretty sure that the II was the last one with Weston speeds.

 

Gerry

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I think John's post #26 sums up incident metering nicely. Hold the meter so that the light hitting the dome or Invercone is identical to the light hitting the subject - as seen from the camera position (with some modification for extreme backlight) - i.e. pointing towards the camera.

 

But - if you know what you are doing - you can also point the meter elsewhere, for determining contrast ratios and the like.

 

The core purpose of using an incident meter is to avoid subject reflectances influencing the meter. If photographing the proverbial black cat in a coal cellar, a reflected meter will give you an 18% gray cat on 18% gray coal, while the incident meter will give you a black cat on black coal (a more accurate representation of reality).

 

Same for photographing your significant other against a white or black wall (or desert sands or snow or bright seascape or whatever).

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  • 2 weeks later...

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Andy's got it right.

 

Incident gives you the general reading for light falling on your subject. Reflective/spot readings would give you the light that is being "returned" or reflected from the subject. Both are useful, but for different reasons. A Zone System photographer wouldn't really have use for incident readings (that I can think of).

 

Those photographers would take the reflected reading of the "black cat in a coalmine" (which would be 18%gray) and then place that value into the "zone" they want the cat's fur to be in, i.e., zone 2 (3-stops down) - very dark gray, almost black; zone 3 (2-stops down) dark gray, starting to have detail, etc. The incident readings would be too imprecise for them, IMHO.

 

But for a street photographer, incident work pretty well, because it speeds up the process and flattens the information. The generalization works pretty well.

 

Use what works for you and the situation. It's all relative anyway.:)

 

Kurt Jones

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I am pretty sure that the II was the last one with Weston speeds.

 

Gerry

 

Hi Gerry

 

My III says Weston rating, but it is an early III and they may well have changed part way through the production run. But it is only a 1/3 of a stop difference.

 

Noel

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Hi Gerry

 

My III says Weston rating, but it is an early III and they may well have changed part way through the production run. But it is only a 1/3 of a stop difference.

 

Noel

 

I'm pretty sure the III is in asa in spite of what it says on the dial, I remember that inconsistency from before.

A google search turned up a current repairer in the UK

 

Weston Light Meter Repair and restore Service

 

in case anyone needs it!

 

Gerry

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  • 3 months later...
Incident light metering obviously doesn't work if the subject is contre-jour.

As a matter of fact, incident-light meterig works perfectly fine also with contre-jour light. You just mustn't operate the meter in the wrong way you were suggesting.

 

 

Just an illustration that the idea of pointing the meter towards the camera isn't entirely correct ...

It's perfectly correct.

 

 

... it presupposes that the light source is behind or coming from the direction of the camera ...

No, it doesn't. Instead, it just presupposes that the camera is seeing the subject from the camera's position ... which can hardly be wrong, can it?

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Note however, that the post of Roger is written for negative film, which has opposite requirements from digital. On negative film you are trying to stop the shadows from being blocked (i.e no information recorded on the film, you can usually open up the highlights and you are using the log curve of the film)) and in digital you are trying to stop the highlights from being blown out, (i.e. there is no detail left because all three channels are maxed out, shadows can be recovered down to the noise floor). That creates essential differences in measuring exposure.

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That creates essential differences in measuring exposure.

No, it doesn't. Instead it just creates slight differences in the interpretation of the metered value. By the way, exposing for digital essentially is the same as exposing for colour slide film. "Exposing to the right" (digital) and "exposing for the highlights" (slide film) basically is the same thing. With colour or B/W negative film you'd "expose for the shadows" (which however is not the same as "exposing to the left"). What does these things mean in practice? Depends on the light, the subject, the media, and your intentions. In particular, when the subject's available contrast matches the recording media's contrast capacity then there is no difference between exposing for the highlights and exposing for the shadows.

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Well, I find these differences rather essential. But then I am a great believer in correct exposure in the camera (which is NOT slavishly following the meter, whatever method it uses) and quite opposed to tweaking in Photoshop or the developer tank, unless strictly neccessary. When I have to slide the exposure slider in raw conversion, I know I have screwed up....

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