[LargeFormat] Bad Kodak Lens

[Jim Hemenway]

I expected to find focus shift on the 13 1/4 - 23 1/4 Protar that I use 
on my 11x14.  But I lucked out.  So far I haven't seen, (or I don't know 
if I've seen) any focus shit on any of my lenses.

Jim - http://www.hemenway.com



Richard Knoppow wrote:

> ----- 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