Re: Realist vs. 4"x5"

[P3D John Bercovitz <bercov@xxxxxxxxxx>]

Hey Eddie!  Here's one that's really gonna glaze your eyes over,
if you read this far.  8-)
 
I wrote:
> Even flat to flat 
> I think a large lens is behind a small lens in angular MTF.  I 
> think it's the film MTF dropping out of the equation which gives 
> large format its advantage, angularly speaking.
> 
> I'd like to check out the curves to be more sure of the first 
> statement in the above paragraph but as far as I know, miniature 
> format lens makers don't publish MTF curves.  I based that 
> statement on my recollection of medium format versus large format 
> curves.  I will check them out tonight if I have time.
 
I looked up the 80 mm f/2.8 Planar made by Zeiss for the Hasselblad
and the 150 mm f/5.6 Apo-Symmar made by Schneider-Kreuznach for 4x5.
These are both normal lenses with focal length about equal to the
diagonal of the format.  In addition, they both have about the same 
coverage, angularly speaking.  Also, they have the same actual wide-
open aperture, essentially.  So I would rate them very comparable.
To top it off, the manufacturers have nicely given twice as many
cycles per mm on the Planar as on the Symmar.
 
150 mm f/5.6 Apo-Symmar
 
f/5.6
             transfer
  5       95%         80%
 10       90%         65%
 20       75%         45%
 
f/22
             transfer
  5       95%         95%
 10       85%         80%
 20       67%         60%
 
So it looks like when you stop this lens down, you lose a little in 
the center and pick it up in the corner.
 
80 mm f/2.8 Planar
 
f/2.8
             transfer
 10       80%         50%
 20       60%         30%
 40       45%         15%
 
f/8
             transfer
 10       90%         85%
 20       80%         65%
 40       60%         30%
 
Using these two lenses as the test case, I have unequivocally 
demonstrated that I'm all wet.  Drat!  Better luck next time.  It 
appears that not only is the film less of a factor in large format, 
so is the lens.  Not good to extrapolate from such a small sample to 
the whole, though, I think.  Anyone know for sure?  (Someone who's 
not just guessing like me?)  Is the Planar a crummy lens?  I didn't 
think Zeiss made crummy lenses.  The Apo-Symmar is not the latest
but it's decent.
 
John B
 
PS: Someone asked how they measure this stuff and I forgot to answer.
It's done with a microdensitometer which is just a really small
hole.  I forget just how small.  Kodak's got it in their literature
on film, I think.  
 
Oh, another thing.  You can do the MTF test with a single "bar" chart
that has a group where the frequency increases as you go from bar
to bar.  Then you can measure the transfer where it's really good
because the cycles are far apart and then compare the transfer where 
the cycles are close together.
 


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