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Scott --
14-May-2010, 07:55
Hi, all -

I became the proud new owner of a Burke & James Petzval yesterday (an Ajax No. 1 Portrait, 9" f/5). The lens has a working aperutre, but with a funky (to me) scale: 5, 6, 9, 15, and 24. If need be, I can measure the physical aperture and figure out f/stops, but I'm just curious - anyone ever seen numbers like those before?

Thanks,
Scott

Steven Tribe
14-May-2010, 10:52
No.

jnantz
14-May-2010, 11:59
it looks like it might be "the stoltz system"

http://www.largeformatphotography.info/forum/showthread.php?t=10569
check out jason greenberg motamedi's post/link ...


the wiki has another fstop chart:

http://en.wikipedia.org/wiki/F-number
( but it doesn't have the stoltz system ) ...


john

Nathan Smith
14-May-2010, 12:02
I guess that could be from the Uniform System (U.S.) of apertures they once used, but it also maybe something altogether different.

Doremus Scudder
15-May-2010, 02:37
FWIW, it seems similar to the Goerz system in the attachment.

Best,

Doremus Scudder

Steven Tribe
15-May-2010, 02:56
I decided that none of the scales in this table really matched the "Ajax" which is described as a Portrait Petzval. Both the fully open value and the range seen wrong for every scale. My guess is that the scale is the modern F scale. How closed is the iris with the F.24 value?

jnantz
15-May-2010, 07:06
scott

you could always measure the iris ( from the front )
and do your own comparison to see what the f-numbers are.
it seems that if it isn't the stoltz system, maybe it is just
regular old fstops ( modern ) but instead of using the number
we are used to, they went by what we might consider half or third stops ...

Scott --
15-May-2010, 09:27
http://www.largeformatphotography.info/forum/showthread.php?t=10569
check out jason greenberg motamedi's post/link ...


You know, the f/stops most closely match the actual f/stop scale at the left of the above chart.


scott

you could always measure the iris ( from the front )
and do your own comparison to see what the f-numbers are.
it seems that if it isn't the stoltz system, maybe it is just
regular old fstops ( modern ) but instead of using the number
we are used to, they went by what we might consider half or third stops ...

I think this is what I need to do - break out the ruler and see what's what. A weird scale, but (hopefully) useable.

Sevo
15-May-2010, 11:53
It is not uncommon to see pre WWI lenses with a "modern" scale offset by one or two thirds. It was not unusual to start with whatever physical opening the lens had, rounded to 1/3 stop, and go on from there in one stop increments, rather than the current standard of marking the standard full stop values, with a 1/3 or 2/3 increment towards fully open if that should be an odd value.

Joe Smigiel
15-May-2010, 15:31
Well, with the exception of the first number (5) it appears the sequence is generated by adding two adjacent numbers together to get the next. It would really be obvious if the first number was 3 instead of 5. (Sorta like the Fibonacci Sequence only different because 3 would need to follow 0 instead of 1.)

0 + 3 = 3
3 + 3 = 6
3 + 6 = 9
6 + 9 = 15
9 + 15 = 24
15 + 24 =39

All divisible by 3. What this has to do with photography however is way beyond me.

I know. I need to get out more.

Jim Galli
15-May-2010, 22:32
I think you guys are all making this too difficult. I had one and never questioned the 5 = f5, 6 = f6, 9 = f9, 15 = f15, and 24 = f24. No, we wouldn't do it this way now, but consider that this wasn't considered that weird at the turn of the century. Heliar had 2 scales, one to make the Germans happy, and one for the Americans, either usable, the German one all in our 1/3rds. 6.3, 9, 12, 18, 24 etc. The Eidoscop is 4.5, 5, 6, 7, 10, and 14. No big deal.