Re: [Rollei] Why the 6-element lens for 3.5Fs

[todd <todd_belcher >]

Richard, I think QG has the 2.8 Tessar in an early Hasselblad mount and 
does not mean the 2.8 Tessar as found in the Rollei TLR.

todd

Richard Knoppow wrote:
> ----- Original Message ----- 
> From: "Q.G. de Bakker" <qnu  
> To: <rollei  
> Sent: Thursday, May 01, 2003 12:29 PM
> Subject: Re: [Rollei] Why the 6-element lens for 3.5Fs
> 
> 
> 
>>Nick Roberts wrote:
>>
>>
>>>As an aside, has anybody ever tried the 2.8 Opton
>>>Tessar?
>>
>>I would love to be able to say how good/bad Zeiss-Opton
> 
> 2.8 80 mm Tessars
> 
>>are.
>>
>>But, alas, i haven't tested the ones i have yet, since
> 
> they need cleaning
> 
>>very badly. No point testing a dirty lens.
>>I have asked the Hasselblad Users brethren (mine are in
> 
> "ancient" Hasselblad
> 
>>mount) if anyone knows how to get to the rear lens group,
> 
> but so far no
> 
>>answer.
>>So maybe there is someone on this list who can tell me how
> 
> to disassemble
> 
>>these lenses (in such a way that they can be reassembled
> 
> again)? Or knows of
> 
>>any resources available anywhere that might help?
>>I'd be grateful for any and all assistance!
>>
> 
>   Exactly which lens are you asking about, the f/2.8 Tessar
> or the Planar?
>   If the Tessar, there is no rear lens group, there is a
> single cemented component. The cell can be unscrewed from
> the shutter but requires some disassembly of the camera.
>   I don't have an f/2.8 Tessar to look at. The f/3.5 front
> cell has a front retaining ring which is removed with a
> friction tool. Probably the f/2.8 is the same. Larger
> Tessars, such as the 135mm, f/4.5 found on old Speed
> Graphics, have a threaded back cap which is easy to unscrew.
> Like many other lenses Tessars tend to get hazy inside the
> front cell.
>   If the back component looks hazy its probably bad cement.
> Recementing is not too difficult but almost all Tessar type
> lenses of any manufacture use a burnished or spun-in
> mounting for the rear component. These can not be opened
> without damaging them. The glass is held in place by a very
> thin lip which is burnished down over the lens. While they
> can be pried up they can never be smoothed down again. The
> usual method for dealing with these is to remove the lip in
> a small lathe and replace it with a threaded cap. Precision
> work.
>   Zeiss lenses of the 1930s and 1940s seem for the most part
> to have pretty good cement; I've seen relatively few with
> edge separation. But the canada balsam used in lenses pre
> about 1950 is sensitive to heat and cold and can oxidize and
> crystalize at the edges if the paint seal is broken.
>   A lot of old lenses which have low contrast are just
> dirty.
> 
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk  
> 
> 

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