Ken,
Did it ever occur to you that the maximum opening may be more of an
advantage to the sales department than to the photographer. After all, many
wide-open shots are made under lighting conditions that preclude any real
judgment of the difference in stops.
Jim Nichols
Tullahoma, TN USA
----- Original Message -----
From: "Ken Norton" <ken@xxxxxxxxxxx>
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Tuesday, April 06, 2010 7:56 PM
Subject: Re: [OM] Dude - Who stole my 0.56ms?
>> 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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