[LargeFormat] Bad Kodak Lens

[Richard Knoppow]

----- Original Message ----- 
From: "philip lambert" <philip.lambert@ntlworld.com>
To: <largeformat@f32.net>
Sent: Wednesday, March 17, 2004 2:07 PM
Subject: Re: [LargeFormat] Bad Kodak Lens


>
> ----- Original Message ----- 
> From: "James Krysan" <jkrysan@sbcglobal.net>
> To: <largeformat@f32.net>
> Sent: Wednesday, March 17, 2004 9:23 PM
> Subject: Re: [LargeFormat] Bad Kodak Lens
> I assume the Symmar S gave the more contrasty image
> Would this be a recent Symmar?  - maybe the Apo was later.
>  My 6&3/8" Kodak Anastigmat is a bit short of contrast.
Would a deep
> bellows hood be an improvement over a conventional rubber
one or would I be
> wasting time getting one?  They can be found sometimes on
eBay.  Not much I
> can do with colour film to enhance contrast. Is this an
argument for not
> buying old lenses? Philip
>
>
> > 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
>
>
>
   Before anything else I would shine a flashlight through
the lens and see if there is any sign of hazyness. Even very
slight haze will lower the contast dramatically. The haze is
easy to clean off but its on inside surfaces so its
necessary to disassemble the lens to clean it. This haze may
not be visible on normal examination. It takes directly
shining a stong light through the lens to show it up. A
clean uncoated lens should be absolutely clear and sparkle.
A coated lens will not have the sparkling look but will be
very clear. Old lenses very frequently have this haze. I
don't know what it comes from but suspect its some volitile
matter from the anti-reflection paint in the cell.
   Another possibility, and one that the flashlight
examination will also show up, is defective cement. Old
lenses, cemented with Canada Balsam, usually show some
effect around the edges. This is most often visible as a
ring of yellowish stain. If not extensive it does little or
no harm. However, both Canada Balsam and the later synthetic
cements can sometimes get cloudy. For instance, I have a
152mm Kodak Ektar with slightly cloudy cement. Looked at
through the 10X loupe it has a very slight orange peel look.
The effect is to seriously reduce the contrast of the lens
leading to a diffuse effect on the image. Its quite visible
on the ground glass. The cement problem is _not_ visible
when simply looking at or through the lens but shows up when
the surface is illuminated with a strong flashlight either
by reflection, at an angle, or by transmission. I've seen
this defect in a much exagerated way in a couple of old
aerial lenses. Synthetic cement can also fail by loosing
adhesion, probably due to lack of cleanliness in cementing
or lack of proper curing. This looks like large bubbles.
I've seen this in some older Wollensak and Zeiss lenses. Its
obvious and is very detrimental to the image.
   A Symmar-S has eight glass air surfaces. If uncoated the
flare would be a bit high but not unusable. This is the same
number of surfaces as a Biotar or Dogmar or Artar type lens.
Its about the limit for an uncoated lens. Tessars have six
surfaces. The flare from internal reflections increases
rapidly with surfaces; its not arithmetic. The flare of even
an uncoated Tessar or Triplet should be fairly low. A
multicoated Plasmat, like the Symmar-S will have lower flare
than a single coated Tessar like the Kodak Ektar, but it
should not be dramatic. Both of these are very well
corrected lenses but bear in mind that spherical aberration
can also look like flare since it produces an overall haze
as well as a sort of halo around highlights. It takes a
pretty bad lens (or a soft focus lens) to give this hazy
image effect.
  ---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com