[LargeFormat] 480 Apo Nikkor Cell Spacing Question

[Richard Knoppow]

----- Original Message ----- 
From: "Michael Briggs" <MichaelBriggs@Earthlink.net>
To: <largeformat@f32.net>
Sent: Sunday, January 25, 2004 9:49 PM
Subject: Re: [LargeFormat] 480 Apo Nikkor Cell Spacing
Question


>
> On 26-Jan-2004 Richard Knoppow wrote:
>
> >  I don't know which type Nikon
> > process lenses are. Their general purpose LF lenses are
slow
> > Tessars.
>
> Nikon process lenses:
> Late Apo-Nikkors are dialytes, like the Artars and
Apo-Ronars.  I have heard
> that earlier ones were Tessars.    The Process-Nikkors
have highly convex outer
> elements and have four elements in four groups.    I an
not sure what the type
> name of this design would be.   Is is related to the
Metrogon?  The
> "Process-Nikkor" is the name of a particularly lens and
shouldn't be confused
> with the Apo-Nikkor, which is a process lens.   The
Apo-Nikkor has narrow
> coverage, as Richard explained, while the Process-Nikkor
is a wide-coverage
> process lens.
>
> Nikon LF lenses:
> Nikkor-M are Tessar designs.  Nikkor-W are plasmats.
Nikkor-SW are
> wide-coverage designs similar to the Super-Angulon and
Grandagon, and would
> probably be classified as Biogen descendents.
>
> --Michael
>

  Several types of lenses have been used for process lenses.
The most common were either "dialytes" or Tessars. I think
some double Gauss process lenses have been made. Later,
Plasmat lenses were made for wide angle use. These were used
for making lithographic plates for offset presses used for
small run newspapers. The whole page was pasted up and
photographed on one lithographic plate. In general, these
did not have to apochromatic and were not.
  The most widely used process lenses for many years were
Goerz Apochromatic Artars. These are four element Dialytes.
This type of lens has four air spaced elements which are all
either bi-convex or bi-concave, or have one plane surface.
The double Gauss type is also, in its basic form, a four
element air spaced lens but in it all the elments are
meniscus shaped and have their concave surfaces facing the
stop. Dialytes are rather narrow in coverage but have very
good corrections. They are made apochromatic for
longitudinal chromatic aberration by choice of glass and are
inherently free of lateral chromatic due to symmetry. They
tend to have rather narrow coverage. Goerz also made an
achromatic process lens called the Gotar. It is similar in
form to the Artar but did not need the special glass. I've
seen only one in the used market. I think Goerz never made
many. Goerz also adopted the Dagor as a wide angle process
lens but it is inferior to the Plasmats for this use and no
cheaper.
  Zeiss made apochromatic Tessars for three color process
work, they were probably the second most used process lens.
  Apochromatic process lenses are used to make three color
separation plates for screen plate type halftone printing.
they must have exactly identical magnification for the three
colors used as well as identical focus. They also must be
free of geometrical distortion. A symmetrical lens is
helpful there because they are inherently free of lateral
color (difference in image size with color), geometrical
distortion, and coma. The relatively high flare of four air
spaced elements without coating is of no consequence in
process work. The plates are extremely high contrast so
flare serves only to shift the threshold a little, easily
compensated for when making the exposure.
  Compared to lenses of the same type used for general
pictorial use process lenses have narrower coverage and are
ususally optimized for equal image and object conjugates,
i.e., distances. Because printing plates are now made by
image burners or directly by laser devices from electronic
scans not many process cameras remain in use. The lenses
have been on the used market for some time. With some
understanding of their limitations they make excellent
pictorial lenses, and especially excellent enlarging lenses.
   The B&L Metrogon and Zeiss Topogon are related to two
lenses. One is the Goerz Hypergon, the other is the double
Gauss. Both are meniscus lenses. The original Hypergon,
designed by Emile von Hoegh, consisted of two deeply curved
and very thin meniscus lenses. It had coverage on the order
of 140 degrees and good correction for distortion. It was
not, however, corrected for spherical aberration or color
and had to be used at a stop of around f/32. The Zeiss
Topogon, designed by Robert Richter, had additional negative
elements inside the postive elements of the Hypergon. It was
corrected for spherical aberration and color. The B&L
Metrogon was further developed from the Topogon by Wilbur
Rayton of B&L. It had an additional element which gave it
much better correction for astigmatism and a flatter field.
Neither the Topogon or Metrogon has the coverage of the
Hypergon, being limited to perhaps 110 degrees. The Hypergon
was designed as a super wide angle lens for general use, the
Topogon and Metrogon were designed as aerial survey lenses.
All of these lenses have terrific light fall off, even more
than the cos^4 theta of theory. The Hypergon had a rotating
special stop to equalize exposure, the Topogon and Metrogon
used tapered center filters. As far as coverage these are at
the opposite end of the spectrum from process lenses.

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