[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 10:52:32 -0500
On 10/28/2010 10:42 AM, Tim Daneliuk wrote:
> 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 :)
Addendum:
The issue here for DSLRs happens both because of the sensitivity
to the angle of incidence of the light AND the fact that SLR
lenses generally are not designed with a huge circle of coverage.
They don't have to - nothing moves on these cameras as compared to,
say, a view camera.
One could probably avoid this problem to a large degree by using
lenses that cover a full sized sensor on a half-frame camera or
even older, manual focus lenses designed for 35mm film on a newer
digibody. The problem there is that Nikon seems to be the only
vendor that has preserved their lens mounts, and even then,
an old AI or AI-S lens does not meter properly on anything but
their highest end digital cameras.
In short, digital makes this a big pain...
--
------------------------------------------------------------------------
Tim Daneliuk
tundra@xxxxxxxxxxxxxx
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