[LargeFormat] Bad Kodak Lens

[James Krysan]

Richard,
I have a 4.5, 101 mm Ektar in a Kodak flash supermatic
labeled "Graphic". I think the S/N is EI495.
It is coated.  I bought it with a mini-Speed Graphic
(graflok back) but I have no idea whether the lens
came originally with this particular camera. Anyway, I
did the test you described and found no evidence
whatever of focus shift. I then checked out a 5.6-100
mm Symmar S and got the same result (thankfully). 
And for my "loupe credentials": it is a home brew
following the idea of Steve Murray in photo.net.
(Briefly, its a 28mm WA for a 35mm SLR with an
extender on the rear of the lens to fix the distance
from the gg). It is at least 10X - probably more - and
it is extremely sharp. Fits my old eyes and small
pocketbook.
Incidentally, on some comparisions I did between the
Symmar and the Ektar (both lenses tested on same roll
of film) sharpness seemed not to be much of an issue,
but the contrast difference was dramatic.
I greatly enjoy your commentary.
Jim Krysan   
 
--- Richard Knoppow <dickburk@ix.netcom.com> wrote:
> 
> ----- Original Message ----- 
> From: "Jim Hemenway" <Jim@Hemenway.com>
> To: <largeformat@f32.net>
> Sent: Tuesday, March 16, 2004 7:14 PM
> Subject: Re: [LargeFormat] Bad Kodak Lens
> 
> 
> > 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
> >
> >
>   I would expect there to be some. However,
> spherical adds
> rather than cancels when cells are combined so the
> spherical
> of a single Protar or Dagor cell is no worse than
> the
> combined lens.
>   I have been using a good quality 10X triplet
> magnifier to
> examine the ground glass image. This is pretty
> critical. Try
> the following experiment. First, focus as sharply as
> possible with the lens wide open. Then stop it down
> two or
> three stops. Then see if changing focus will sharpen
> the
> image any. If it does, then open it again and look
> at the
> image with the lens wide open. If there is focus
> shift you
> will find a definite difference in the focus
> positions for
> the two stops. The larger error as far as defocusing
> is in
> the wide open image after focusing critically when
> stopped
> down. Generally, the lens will move away from the
> ground
> glass as you stop down.
>   Since last posting I've compared two Speed Graphic
> Zeiss
> Tessars of late 1930's construction and a Bausch &
> Lomb
> Tessar of considerably older vintage, the latter on
> a view
> camera. Neither Tessar has much focus shift although
> both
> have a little. One is slightly better than the other
> and is
> a lens I've always considered extra sharp. The B&L
> Tessar is
> quite sharp but shows some shift. Its hard to
> compare
> because its a longer FL lens, but, from the amount
> of
> softness of the wide open image, its probably not
> quite as
> good as the Zeiss lenses. I think focus shift is
> mainly of
> concern when some method of focusing other than
> looking
> directly at the image is done. Even the Kodak Ektar
> that
> started this all off is actually a very sharp lens
> when
> stopped down, its just that the critical focus using
> the RF
> is too far from the actual critical focus. I had not
> realized before just how much focus shift many
> lenses have.
> 
> 
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@ix.netcom.com
> 
> 
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