> Is the combination of #1 & #7 valid? I'm not saying it isn't, just
> asking? Is it the same using a lens in focus vs. WAY out of focus?
>
I think so. The point is that by having it at infinity focus I had no
light-loss due to extension which might have created another variable to
question. The screen was essentially a flat translucent light-source.
> Is it possible that, as the shutter speed gets higher, the sync
> frequency of the screen starts to affect the exposure? I was concerned
> with both possibilities when testing using a small, daylight fluorescent
> light table.
>
I was thinking that might have been an issue too, but it wasn't. I verified
it to 1/2000 with other apertures.
> I have no answer, except to guess that DSLRs may not be good measuring
> tools for this issue, for as yet unknown reasons, at least to me.
>
Hmm. I have a theory starting to emerge. I carefully duplicated the test
sans-film with the OM-4T on my laptop screen using the spot-meter mode and
observed that the F1.4 position was 1/3 stop off from the other apertures.
This is much better than the 2/3 stop of the E-1. Therefore, I got to
looking at the cameras a little closer.
The exit pupil of the 50 F1.4 is rather huge and the mirror chamber of the
E-1 is tiny in comparison. What I'm thinking here is that the actual mirror
chamber itself isn't large enough to support maximum aperture of the 50
F1.4. As to the spot-metering of the OM-4T being off by 1/3 a stop, just
maybe the same thing is happening there too.
> I still differ with your assumption that the smaller aperture opening
> change means the lens is not f1.4. That conclusion can't be logically
> drawn from the purely relative data.
>
If I implied or stated that the lens is not a F1.4 lens, my apologies. It it
is a mystery that I'm trying to get to the bottom of. Based on hard-testing,
it is absolutely true that the lens on the E-1 is unable to give me a full
F1.4 aperture and I was trying to figure out why.
My current theory is in-camera vignetting which has nothing to do with the
lens. If so, this is a problem for regular FourThirds cameras, but with the
shallow chamber of the MicroFourThirds, it might be just fine.
> The 1984 Modern Photo test of 50/1.4 #1,136,552 shows a tested aperture
> of f1.44. As the tested focal length is slightly long at 50.94mm, the
> calculated aperture if it were exactly a 50mm lens is 1.4134, almost
> exactly the theoretical value of 1.414. I tend to go with MPhoto, as
> they were in the forefront of lens testing at that time.
>
Sounds good to me. At this point, I'm going to concur with this and just
blame the cameras.
> Ready to do a test on film? Got a densitometer?
>
My RHDesigns analyzer has a densitometer mode. At this point, I might not
bother. OTF metering will compensate accordingly so it's a non-issue.
AG
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