I think Ole is right! These "diameters" certainly represent a halving of the aperture area for each stop down. This kind of aperture marking makes sense with casket (trousse in this case) so that the user refers to the attached tables. I have a casket set from Berthiot with absolutely no markings on the wheel aperture.
Thank you Ole, Steve,Originally Posted by Ole Tjugen
this is exactly what I was thinking about today while dismantling the lens for cleaning and manufacturing adapter to Copal 3. Wide open it has cca 30mm diameter. (I didn't have right slide gauge to measure it).
Do you know what type of lens it is? Looks like RR but I'm not sure because I wasn't able to loosen the rear part.
K.
Last edited by kapro; 6-Mar-2012 at 13:10. Reason: Question mark
RR is always a possibility with old lenses. A 250mm f:8 RR (or Aplanat, or Aplanatique) would have a max aperture of about 31mm - so maybe you can measure the focal length?
It might be. When it came I made a projection of ceiling lights on the floor (4-5m high) and it was sharp when lens' aperture ring positioned around 23-4cm from the floor (just very fast and uncertain measuring of focal length). I'll measure it when I'm back home on Thursday.
Thanks a lot Ole.
And post some photos at the same time?
Berthiot is a problem child as no early catalogues for the first years have been available on-line (including France).
Steven,
here are some junk photos of my Berthiot No.4
Sorry for the quality, I don't know to work with colleague' s digital camera.. ;-)
And here is mine for comparison of serial numbers ( a bit dark but it is 22606) and engraving style.
Mine is size 3bis and is a casket set. Note our serial numbers are close!,
Steven, do you know production year of yours? My should be little bit older.
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