Hi Chuck,
As I understand, the need for centre filters largely have to do with
the type (design) of lens,
and how much of the lens' angle of view one is using. It's not at all
simply a fector of
focal length.
The Schneider Super-Angulon lens design has an extremely wide angle of
view and huge image circle,
and thus need centre-filter compensation. Ditto for the Super Symmar
(Aspheric) lenses. This applies
for all focal lengths: From the ridiculously wide SA 47mm to the 90mm,
and the Super Symmar lenses up to
210mm if one is using the full (huge, covers much more than 8x10in)
image circle.
On the other hand, the very very wide Nikkor 60mm f/4 has a much
smaller image circle (just covers 4x5in,
and certainly not 6x17cm) yet it is a fast lens, but does not require
a centre filter. Completely different
optical design.
The Scheneider Apo Symmar L lens series (120mm to 480mm) do not need
centre filters, nor do the
Makro Symmar HM (80mm to 180mm). I don't know the Rodenstock LF lenses
very well, I only use their
enlarging lenses :-)
In short: I do not know enough about optical theory to say why this
is, but there you go. The PDFs
downloadable from Schneider-Kreuznach's website explain which lenses
need which filters, and have a nice
comparative diagram of the image circles / angles of view of all their
lens designs compared.
Anyway, at f/22 all LF lenses look amazing, and some of them look
great closer to wide open. I have shot my
SA 90mm XL wide open (f/5.6) on many occasions, and the overall image
detail on a 6x17cm slide is still
staggering - still much much better than what you will ever get out of
a small sensor with the best lenses.
But it's clearly inferior to the rendering at f/11 onwards - then it's
a detail demon.
kind regards,
Dawid
On 27 Dec 2009, at 2:56 PM, Chuck Norcutt wrote:
> Thanks for your detailed reply... and your very detailed image. :-)
> Do you know of any documentation on the need for center filters? eg;
> Brian says not needed at 115mm but you say 90mm does need one.
>
> Chuck Norcutt
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