[pure-silver] Re: Neither My Hassy Nor View Camera Have This Problem
- From: Tim Daneliuk <tundra@xxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 28 Oct 2010 10:42:59 -0500
On 10/28/2010 10:24 AM, Howard Efner wrote:
> TTL metering will compensate for the difference in transmission since it
> measures light after the optics.
>
> Establishing an "effective film speed" will also compensate for lens
> transmission, shutter speed errors, f/ stop calibration errors, light
> meter errors, and GOKW.
>
> Thank God for that old, obsolete, technically inferior, film!
>
> Howard
>
In rereading this article, something else jumped out at me. In traditional
film photography, there is some light falloff at the edges of the circle of
coverage. This is particularly pronounced in the shorter focal lengths.
IIRC, this is due to both the innate characteristics of the lens design,
and the angle at which light is traveling relative to the plane of the film
... which is most pronounced at the edge of the circle of coverage.
However, if the circle of coverage is considerably larger than the
negative, the effect is negligible. For example, I have a Schneider SA-XL
72mm. The lens will cover 5x7, but, since I use it on a 4x5 camera, I don't
see significant light falloff.
With digital sensors, though, the angle makes a really big difference
because - as the article mentions - the sensors are typically light
sensitive "tubes" - if you hit them at too oblique an angle, the photons
don't "fall down the tube", so to speak, and you effectively get light
falloff.
Since I shoot nothing serious with digital, I've never much paid attention
to this artifact ... I've been too busy being frustrated with the lack of
dynamic range :)
------------------------------------------------------------------------
Tim Daneliuk
tundra@xxxxxxxxxxxxxx
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