Re: [Rollei] Can I read some comparisons - 3.5 Xenotar vs. Planar?

[Richard Knoppow <dickburk >]

At 06:43 AM 12/11/2001 -0500, you wrote:
>Can I read some comparisons between the Rolleiflex 3.5 Xenotar vs.
>Planar?
>
>Same for the 2.8 versions?
>
>Does anyone have experiences to share, or web sites to direct me to?
>
>Thanks
>Vick
>
>
  A serious answer. This has been discussed to death many times. A Google
search will turn up probably hundereds of Usenet threads and stuff on web
sites.
  In fact, there is probably minimal difference among these lenses. Testing
lenses is fraught with possible errors plus even the apparent performance
of the cameras in practical use depends on how well the finder lenses are
synchronized to the taking lens. 
  The subject is further complicated because two variations of f/3.5 lenses
were offered by both manufacturers, a five element lens similar to the
f/2.8 and a sixe element lens, pretty much a conventioal Biotar type.
  Schneider's five element f/3.5 lens is the same design as the f/2.8 lens
but the Planar is not. The five element f/2.8 Planar has its cemented
surface in the front component, the f/3.5 Planar in the third component.
This design is probably cheaper to make than the f/2.8 because the cemented
surface is plano and the very thin front element of the f/2.8 lens is
eliminated. 
  Both Xenotar designs use a plano cemented surface in the second component.
 The five element lens is derived from the original six element type by
combining two elements at front or rear and elminating one cemented
surface. Zeiss and Schneider went about this in slightly different ways but
were trying to meet the same specifications. I am not sure why the six
element design was adopted for the f/3.5 lens, its the faster lens one
would think would require the greater complexity. 
  One possibility is cost plus weight and size may have been
considerations.  The Tessar is not a very satisfactory lens beyond f/3.5 (I
am not refering to the defective Tessars used on early Rollei cameras but
to the generic design). Adding an element is a way of improving the
performance at larger apertures, especially away from the center of the
image. It may be that a six element f/2.8 lens would have been too large
and heavy for use in a TLR. The smaller f/3.5 lens may have alowed the use
of the more conventional design. I don't have any idea of relative costs of
the two types but it is not impossible for the sixe element lens to cost
less, despite the need for both an additional element and the cemented
surface (cemented surfaces are expensive to make) if, perhaps, some cheaper
type of glass could be used. 
  Marc migh have some insight or inside information about this. In any
case, all six lenses were intended to deliver deluxe performance, whatever
method was used to get it.  
  All six of these lenses are of suberb performance although people
certainly have preferences. 
  
- ----
Richard Knoppow
Los Angeles, CA, USA
dickburk  

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