## Re: [woodandbrass] Waterbury Lenses

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• Thanks for the info Rob. In a message dated 11/28/2011 5:08:12 P.M. Eastern Standard Time, idag@pce.net writes: Dan, The markings on your revolving Waterbury
Message 1 of 5 , Dec 1, 2011
Thanks for the info Rob.

In a message dated 11/28/2011 5:08:12 P.M. Eastern Standard Time, idag@... writes:

Dan,

The markings on your revolving Waterbury stops represent a ratio to be applied to the specific focal length lens being used - in order for the photographer to calculate how much extra exposure time was needed, compared to using the lens wide open.

Here's an explanation from W. K. Burton's 1891 Photographic Optics, p. 57, which I have in my library, and which you can find doing a Google Book Search.  Put on your math hat and apply the formula below to the focal length of your lens using the Waterbury numbers (15, 20, 25, 35, 60) marked on your revolving diaphragm.

The last paragraph in the following 1887 Waterbury advertisement could be a clue as to Waterbury's choice of diaphragm openings (apertures), which seem to be rooted more in a given lens's practical application - rather than simply reducing the light by a set-amount with each smaller-sized opening.  "It has diaphragms of three different diameters, these being carefully calculated so as to suit the various exigencies under which a lens is employed."

Cheers,
Rob McElroy
Buffalo, NY

On Nov 25, 2011, at 9:57 AM, dcolucci@... wrote:

On the internet I have seen a few posts that the Waterbury lenses are f/12 wide open.  Yet, on post 1887 models with revolving diaphragms and hole markings at 15-20-25-35-60 - why wouldn't you assume those are f stop numbers?

In an 1891 ad, it mentions these numbers as  " f / 15" :

<Untitled.jpg>

And I missing something or is this an f/12 lens ?

Thanks
Dan

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