Xenotar 135mm f/3.5 coverage question

I have just acquired a 135mm Xenotar f/3.5, and I'm somewhat surprised by
the coverage it seems to give. Schneider claim on their website that it
gives a 153mm image circle at f/16 and infinity focus, which *just* covers
5*4, and indeed a search of various web forums, as well as archives of this
group suggests that this lens isn't great for 5*4 view camera use because it
doesn't allow for any movements.

However, I figured that this wouldn't be too much of a problem, as I can use
it with a rollfilm back, where it will make a nice portrait lens, as well as
using it for some 5*4 landscape stuff, and macro work.

However, when I mounted it on the camera, I was pleasantly surprised to note
that, on focusing at infinity, there appears to be plenty of coverage. I can
apply a fair bit of shift and the image still covers the entire focus
screen. The edges dim a bit, but the image is still there, and seems
relatively sharp (difficult to judge without taking a photo, of course).

Any ideas about this apparent discrepancy? Perhaps it's the case that the
quoted circle size is for a certain level of sharpness/vignetting, and that
there is a usable image outside this circle, but it may lack sharpness, or
maybe Schneider are just very pessimistic with their coverage figures?

On 3/22/2005 11:59 AM Chris Brown spake thus:

 > I have just acquired a 135mm Xenotar f/3.5, and I'm somewhat surprised by
 > the coverage it seems to give. Schneider claim on their website that it
 > gives a 153mm image circle at f/16 and infinity focus, which *just* covers
 > 5*4, and indeed a search of various web forums, as well as archives of this
 > group suggests that this lens isn't great for 5*4 view camera use because it
 > doesn't allow for any movements.
 >
 > However, I figured that this wouldn't be too much of a problem, as I can use
 > it with a rollfilm back, where it will make a nice portrait lens, as well as
 > using it for some 5*4 landscape stuff, and macro work.
 >
 > However, when I mounted it on the camera, I was pleasantly surprised to note
 > that, on focusing at infinity, there appears to be plenty of coverage. I can
 > apply a fair bit of shift and the image still covers the entire focus
 > screen. The edges dim a bit, but the image is still there, and seems
 > relatively sharp (difficult to judge without taking a photo, of course).
 >
 > Any ideas about this apparent discrepancy? Perhaps it's the case that the
 > quoted circle size is for a certain level of sharpness/vignetting, and that
 > there is a usable image outside this circle, but it may lack sharpness, or
 > maybe Schneider are just very pessimistic with their coverage figures?

I think your last statement is the explanation; others have said here that
this manufacturer's coverage figures are quite conservative, which is a good
thing (always nice when something actually performs *better* than advertised).

This reminds me of the results I had using an older lens (an uncoated CZJ
Tessar) past its supposed limits. I mounted a 105mm Tessar on a 9x12 (cm)
plate camera as a semi-wide angle lens. I was astounded at the results:
absolute corner-to-corner illumination AND sharpness.


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