[LargeFormat] 5x7 Lens Information

[Clive Warren]

At 5:19 pm -0700 30/8/02, Rich Lahrson wrote:
>Hi!
>
>     I'm still in the 'looking' stage for a lens for the 5x7 Seneca.  This lens
>seems interesting,
>albeit painfully slow:
>
>http://cgi.ebay.com/ws/ebayISAPI.dll?MfcISAPICommand=ViewItem&item=1377439048&indexURL=0&photoDisplayType=2
>
>F/14, that's just shy of f/16.  It may cover 8x10 with some 
>movements.  Anyone use
>anything like this?
>The discription mentions Steve Grime's fixing them for use.
>
>Cheers,

Rich,

The lens you mention is a SOM Berthiot 120 mm Perigraphe lens that 
the seller states covers 8x10 with movements.

I may be completely wrong about this but I would guess that it is a 
5x7 lens that will cover 8x10 when stopped down. Maybe there are 
others who are more familiar with the SOM Berthiot lenses. Looks like 
a Protar type design. Quite a few of us on the list use Protar 
lenses, but usually on bright sunny days :-)

I would be very interested in seeing one of the Steve Grimes 
conversions as there are a couple of lenses here of similar 
dimensions that need mounting in shutters.

There are a number of options (excluding a Packard shutter approach):

1.Use a fairly large shutter to avoid vignetting that huge image 
circle and front mount the lens. The disadvantage with this approach 
is that you take a compact lens and make it a large lens by virtue of 
the size of the shutter required to avoid losing any of that image 
circle when the lens is front mounted.

2. Convert a smaller shutter to take the lens and dispense with the 
original lens barrel.

3. "Sink mount" the lens within the shutter so that the rear element 
is as close to the shutter as possible and retain the original iris 
diaphragm in the barrel. This makes the shutter iris redundant.

Option #2 seems to be the optimum solution but probably the most expensive.

It would be a lot cheaper for you to find a good Wolly 210mm or well 
used contemporary 210mm and at least try the format before committing 
to an expensive exercise.

HTH

Cheers,
        Clive