[pure-silver] Re: Uncoated lenses
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 31 Dec 2008 12:34:05 -0800
----- Original Message -----
From: mmagid3005@xxxxxxx
To: pure-silver@xxxxxxxxxxxxx
Sent: Tuesday, December 30, 2008 8:26 AM
Subject: [pure-silver] Uncoated lenses
I want to use an old f/6.3 uncoated Tessar from a 9 X 14 ICA
folding camera. Is there a filter I can use that will
simulate the effect of a coated lens?
Marty
BTW, While the f/6.3 Tessar was probably an economy
model Tessars work very well at this speed. One of the
inherent problems of the Tessar type is an aberration called
oblique spherical aberration. This looks something like coma
since it results in a smearing of points in the image toward
the periphery and is proportional to the stop. All Tessars
have this fault to some degree but, since it is proportional
to the stop (reduced by stopping down) it tends to be worse
in faster lenses. f/4.5 Tessars generally must be stopped
down to around f/8 to f/11 to get rid of it. There should be
less in the slower lens. The slower lenses are also smaller
and lighter than faster ones.
Check the front cell of this lens for a cap on the
back. Generally, Zeiss used caps on the backs of longer
focal length lenses and retaining rings on the front of
those with shorter FLs. The caps are easily removed for
cleaning the inside surfaces of the elements. Where a
retaining ring is used a friction wrench must be used for
removal. This is simply a tube the right diameter to fit the
ring with a ring of sticky rubber on one end. The design of
the cells is such that elements are automatically centered
by the cap or ring. These touch the surface of the element
along a ring shaped knife edge. A spherical surface will
always be brought to the center of curvature by such an
arrangement.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
