[LargeFormat] Bad Kodak Lens

[Richard Knoppow]

----- Original Message ----- 
From: "Jim Hemenway" <Jim@Hemenway.com>
To: <largeformat@f32.net>
Sent: Tuesday, March 16, 2004 11:59 AM
Subject: Re: [LargeFormat] Bad Kodak Lens


> Hi Richard:
>
> I have a camera like yours which is in good shape with
nothing wrong.
> but I also have the newer model with the 105mm f3.7 Ektar
and also with
> both focal plane and between the lens shutters.  The
rangefinder was in
> such a twisted, screwed up condition that even after I had
replaced the
> mirror, I was unable to make it work properly... and the
front standard
> was warped.
>
> Without your kind of persistence, I gave up and brought it
to Mike Zak
> in Providence... all was fixed for $80 and was well worth
it to me.
>
> Jim, "I fear that I'm turning into a camera collector"
Hemenway
>
>
   The 105mm, f/3.7 is a Heliar type and should be of
outstanding quality. This is essentially the same lens as
used on the Medalist camera. According to the patent the
extra element was used to improve "rim ray" correction so
that the lens will perform better when wide open.
   My 101mm Ektar is _not_ a horrible lens. When stopped
down it is quite sharp. The problem is excessive focus shift
from wide open to medium stops. This means that no matter
where I set it up with the rangefinder it will be not quite
in focus somewhere else. Other Ektars I have do not have
this problem nor do the two Wollensak Optar/Raptar lenses I
have although the Raptar has too much coma. I checked both
of my older Zeiss Tessars (on Speed Graphics) and found they
do have some focus shift although the focus stays within
reasonable limits. This is not something I expected to
encounter although I knew that some types of lenses have too
much focus shift to be used with rangefinders (Dagors for
instance).
   BTW, I wrote a note to the Rolleiflex list because this
same problem can exist with reflex cameras as well as
rangefinder cameras, or, for that matter, for any camera
where the image is not directly focused on ground glass.
Even SLR's can have the problem because most have automatic
diaphragms and are focused wide open. This suggests to me
that at least some of the complaints about film flatness in
roll film adaptors may actually be from focus shift where a
rangefinder camera is used or where the ground glass is used
but the image not checked for focus at the working stop.
Actually, most focus shift in a lens is gone after its
stopped down about two stops from maximum aperture, though
you may have to go three stops for some. I would have
thought that depth of field would compensate but its obvious
from the ground glass image that it doesn't. Of course, this
would also cause somewhat unsharp images when using sheet
film and the ground glass if focus is not checked at the
working aperture.
   Note that the lenses I've had this problem with are very
old. I doubt that there is significant spherical aberration
and attendant focus shift with current high quality lenses,
but I don't have one to check. I think its worth a few
minutes with a loupe to find out.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com