>I must say that I modified a 2-4 for my OM-1 and the screen brightness is
>dramatically better. Now I can use the fine details in the composition for
>focus. I'm going to put one of those in my OM-2 too.
>
>John
Wouldn't being able to see fine detail have to do with the fineness or
courseness of the ground glass rather than the amount of light transmitted
by the fresnel lens?
I did say it looked different. For instance, without a lens you could see
colored shapes through it, unlike the 1-13 which was uniformly
illuminated. That would indicate a finer texture. But I could not really
detect any noticeable difference except in a worst case scenario of trying
to focus a really slow lens(F8) in a daylit room with some light from the
window. The difference was just perceptible. The difference between
focussing maybe, and focussing with some(but not a lot)certainty.
It does seem to me that with all the equipment mavens on the list that the
discussion could gain some objective information if someone set up a test
situation with a hand held spot meter that could measure the difference
coming through the viewfinder with the same target and different screens.
Then maybe it is me. Since so many have talked about the dramatic
difference of even 1 or 2 fStops, I just looked through my 24/2.8 with a
reasonably bright overcast twilight outside. I set the FStop for F4 and
looked through the viewfinder and used the stop down button on the side of
the lens. Then I tried it at F5.6. Outside where it was relatively bright,
I could just barely tell I stopped down to F4. If I looked, before and
after, without watching the transition, I could not tell any difference.
Inside in a fairly dark TV room the difference was more noticeable and wide
open I felt a little more confident about what would be a questionable
focus at F4. 2 stops difference was more noticeable, but hardly what I
would call dramatic except in the darkened room. The difference I noticed
between the 1-13 and 2-13 before was similar to the 1 stop difference I
detected stopping down. So I would guess that the screens may have a 1
stop difference. The results were similar to what users of slower lenses
experience. They are perfectly usable and not that much different than a
fast lens in most situations, but you wish you had a faster lens to get a
shot of that person standing in a doorway in a rainstorm.
So if low light focussing is your thing, probably you should buy fast
telephoto lenses so that the depth of field lets focus pop in and out on
the ground glass, or buy a Leica rangefinder and fit it with shorter focal
lengths.
It is easy to perceive larger differences than there are. Hey, my car
drives faster and smoother after it has been to the carwash, too. That is
probably why people really like lens tests when they are consistently and
carefully done.
Winsor
Winsor Crosby
Long Beach, California
mailto:wincros@xxxxxxxxxxx
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