Som Berthiot Eurygraphe #3 casket set.

Hi
I have recently purchased this set which includes two 305mm cells and one 575mm cell, the iris scale is in millimeters, could anyone tell me the aperture settings for each cell seperately and for the combinations or indeed the formula so that I can calculate for myself, also I have read posts on this forum which have mentioned other focal length cells in different sets, has anyone come across anything longer than 575mm, do all the cells have the same mounting thread as I am thinking I might pick up another set with different focal length cells?

Any info greatly appreciated:) :) :)

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Originally Posted by Tony Lakin

Hi
I have recently purchased this set which includes two 305mm cells and one 575mm cell, the iris scale is in millimeters, could anyone tell me the aperture settings for each cell seperately and for the combinations or indeed the formula so that I can calculate for myself, also I have read posts on this forum which have mentioned other focal length cells in different sets, has anyone come across anything longer than 575mm, do all the cells have the same mounting thread as I am thinking I might pick up another set with different focal length cells?

Any info greatly appreciated:) :) :)

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Bump

I've been looking, and found - just about nothing about this set.

The Vade Mecum has this:

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Eurygraphe f6.3 Symmetrical anastigmat, probably of 3+3 type.
The example seen was very impressive with 3 cells in a casket, and seemed to be of Q9 type though an extra reflexion might have been present. It offered cells at 305, 390 and 575mm and pairs at 180, 205 and 240mm, ideal perhaps for 5x7 or 1/1plate. The iris was graduated in mm. It is inherently a very desirable item.

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Since the f-stop is defined as d/F (or F/d to get the number directly) where F is the focal length and d is the diameter of the entrance pupil, calculating the f-stop is easy. It's especially easy when the entrance pupil is identical to the phydical aperture as with a single cell behind the stop, but for focal lengths in this range the error from making the same assumption with a lens cell in front is negligible.

Thanks Ole:) :) :)
I had already found the info on the Vademecum, the info on calculating the aperture is most helpful, I have had a closer look at the set today and it a Eurygraphe #3 series IVc serial No.935574 the coverage and focal lenghts are approximately as follows.

305mm= 305mm will cover 11X14 inches stopped down to 10mm

575mm= 575mm covers at least 11X14 inches wide open.

575mm + 305mm = approx. 210mm covers 6.5X8.5 inches stopped down to 6mm.

305mm + 305mm = approx. 170mm covers 5X4 inches stopped down to 8mm.

these figures are based on seeing the full aperture through the clipped corners of the ground glass ie full illumination and all would cover more with gradual fall off. I don't know about sharpness until I can fabricate a lens board to enable me to use my Sinar shutter and shoot some film.