Voigtländer & Sohn Braunschweig Euryscop help needed

[hendrik faure]

below is my most used lens for years, I do not know age and exact type, under the tape is engraved "euryscop". I use it on 8x10, which is covered, the lens board is deardorff-size 6x6inch
estimated focal length 12 inch, diameter of front lens 2 inch, diameter of back lens 2 inch, overall length of barrel about 3 1/2 inch.
Waterhouse stops are lost, I have one made from paper (works f16 or f32, I do not know for sure) and I want to build better new ones.

my questions:
what f-stop may this lens have fully open?
which diameter of hole in the waterhouse- plate must be for f-stops of 8, 16, 32?
and (less important) does anybody know, which stops had the original plates for this lens????

thanks a lot
hendrik

http://i1322.photobucket.com/albums/u568/hfa8/Euryscop_zpsd5b753fc.jpg

[Tim Meisburger]

Its an f/6. Calculate f by dividing focal length by diameter. 12/2 = 6

f/8 diameter is 1.5 inches
f/16 is 3/4 inches
f/32 is 3/8 inches

Remember that this is (relatively) accurate only for infinity focus. If you focus closer then actual f will be a function of actual focal length. For example, if you focus on a nearby object and have 24 inches of bellows extension instead of twelve, then your working focal length will be 24", not 12", and the aperture wide open will be fl/d = f, or 24/2 = f/12.

Hope that is clear.

[Steven Tribe]

Can't quite read the serial number - is it 34xxx?

F.6 is the series IV and this one was later called size 3 (perhaps there is a 3 under the tape as well?). This is designed for up to 10x12". The flange problem could be solved as Voigtlander used standard sizes across models.
Voigtländer say the focal length is 11.5" and the front lens has a diameter of 2 1/6".

The effective diameter of max aperture is the restrictive diameter of the diameter seen from the front - which, of course, is a real problem to measure!!

But 11.5 divided by (F) 6 give just 1.92".

11.5 divided by 8 gives 1.44" - so hole diameter 1.44" is F8

11.5 ditto 16 ditto 0.72" ditto 0.72 is F18

and diameter .36" is F32.

These are near enough to effective size not to matter.

I happen to own a set of waterhouse stops for this lens. There were at least 5, perhaps 6. The diameter I have are:

missing?
39.5mm
31.4mm
22.6mm
missing
8.9mm
missing?

[hendrik faure]

Steven and Tim,
these informations are clear and help, thank you very much!
Indeed I often do still life with long bellow extension
The serial number is 34994. Under the tape is only euryscop, no number near to it (but I did not unwrap completely)
hendrik

[Steven Tribe]

There is a great deal of doubt about the manufacture dates of early Voigtländer serial numbers. But yours is either late 1888 or early 1889 and is past the period of "uncertainty"!

The "3" will be close to edge of the barrel and is quite small.