[LargeFormat] Double Protar Lens

[Clive Warren]

At 7:20 pm -0400 1/9/03, LNphoto wrote:
>>Thanks for all the replies.
>>
>>It seems that my confusion lay in the fact that the lens is in a 
>>shutter with two aperture scales. I do not have the beast yet, but 
>>it seems to be a single 11" approx. Series VII - ie half a double 
>>Protar, probably placed in the shutter some time after its 1895 
>>manufacture. More than likely it is f12.5
snip
>
>According to my 1911 catalog, a pair of 11 3/16" cells give a 
>combinded focal lenght of 6 3/8" @ f6.3 and covers 4 1/2 x 7 1/4. 
>Something tells me in later years that was rounded to 5x7.    The 11 
>3/16" cell alone will cover 6x8 (whole plate) and has a back focus 
>of 12 7/16".
>
>I have a couple of B&L double protars....enough to make a D set.  I 
>also have C+ set from Zeiss.   While the glass may be similar, you 
>have to remember these were made with "native" machines.... The 
>Zeiss is metric through and through,  The B&L is Yankee.  The Ross 
>may be "stricken" with Whitworth threads, so that tube may need 
>different threads at one end than the other.
>
>Les

Les,

Thanks for that. You've hit the nail on the head. It could indeed be 
a pair of 11 3/16" cells. I'l let you know when it arrives! Seems 
strange to supply a double Protar with two identical cells. Making 
them triple convertible with two unequal focal length cells would 
have increased the value and utility.

Moore and Wright tell me that the OD of the threads for a single cell 
is 60.4mm and Mr Moore and Wright Whitworth thread guages tell me 
that the rate is 32TPI. The tables are out in the garage, but it is 
too fine a thread to be Whitworth. It is probably something strange 
though.....

The tube for the current Ross Double Protar would be a simple 
mounting plate for the Betax shutter to allow the lens to be front 
mounted. The flange threads are 69.6mm at 24TPI.

If you have a thread guage handy it would be interesting to know the 
rates for your Protar cells.

Cheers,
        Clive