[LargeFormat] Bad Kodak Lens

[Jim Hemenway]

Sorry, I really meant shift... really!  <no grin>

Jim Hemenway wrote:

> 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
> 
> 
> 
> 
> 
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-- 

Jim - http://www.hemenway.com