Rapid Angulaire Lens

[seawolf66]

I just received this lens its a 4 inch lens approximately 35mm high and 40mm wide for the body,
Like a fool I did not check to see if the wheel for stops had numbers , well it does not have any
numbers on the rotary stops wheel, is there a simple way too figure out the apertures on this wheel

please no geometry or other fancy calculations only 8 Th grade educated

the largest hole is 10mm
next largest is 8mm
next is i think 4mm
next is i think 2mm

thanks for the help

[vitality]

You mean F-numbers?

Focal length / diameter of aperture = F number.

e.g. you have 100mm (4 inches) FL, biggest hole is 10mm -
100/10 = 10 (so, this one will be F/10)
next aperture has is 8mm diameter -
100/8 = 12,5 (this one F/12,5)
etc...

[Steven Tribe]

An "F10" is a bit unrealistic for this type, so a check of the focal length is called for!
The "Martin" must be a retail outlet. The engraving distribution on the barrel is very similar to early Berthiot wide angles and casket sets, so they may have used them as a model or even as a source.

[Steven Tribe]

How the lack of a front lens escaped me - I have no idea!
These wide landscape type are typically around F11.

[seawolf66]

Steve: the front lens is next to the it, I removed the lens so as to show the F-stop's
on the wheel better

How the lack of a front lens escaped me - I have no idea!
These wide landscape type are typically around F11.

[seawolf66]

So could I safely think that F-11 would be the largest opening and
the next would F-16 and then F-22 and then F-32 for testing purpose
just for testing purpose's

[Steven Tribe]

It is quite unusual (but very useful for "alternative" photography!) to have an f stop outside the manufacturer's recommended limit.
Otherwise they are all F16, F15, F16 etc.
The presence of the F10 stop could be a suggestion from the maker that the rear achromat could be used as alone with its much longer focal length - but, of course, no longer F10! There were plenty of casket aplanat sets from France which were dual single/double cell recommended.

I suddenly remember that I sold a similar anon. wide angle aplanat a few months ago. This had illogical F values for the different size holes. It is obvious (now!)that some of these values refered to normal use and some for the use of the rear cell only! And I thought it was because of a drunken engraver!

[Ole Tjugen]

If the holes are 10, 8, 4 and 2mm and the focal length is 100mm, then the apertures are as follows:

100/10 = 10
100/8 = 12.5
100/4 = 25
100/2 = 50

So f:10, f:12.5, f:25, and f:50.

Do not assume that old lenses will have apertures in the "standard modern series" - f:8, f:11, f:16, f:22 and so on. There were many different "series" in se, and many do not even follow THOSE!

French lens makers seem to have had a preference for this series, ending at a nice even f:100. The 12.5, 25, 50 is rather common.

[seawolf66]

thank you very much Ole. well that should be fun with a Light meter, the funny part is this lens could almost fit in a watch pocket
thanks again Ole :

If the holes are 10, 8, 4 and 2mm and the focal length is 100mm, then the apertures are as follows:

100/10 = 10
100/8 = 12.5
100/4 = 25
100/2 = 50

So f:10, f:12.5, f:25, and f:50.

Do not assume that old lenses will have apertures in the "standard modern series" - f:8, f:11, f:16, f:22 and so on. There were many different "series" in se, and many do not even follow THOSE!

French lens makers seem to have had a preference for this series, ending at a nice even f:100. The 12.5, 25, 50 is rather common.

[premortho]

If you have a Weston Master, it has a lot of the "other" f-stops on the dial. Even if it does'nt work any more, just set the Weston to agree with your working meter, than read off the exposure at-or-close to your f-stops on the rotary wheel stops.

thank you very much Ole. well that should be fun with a Light meter, the funny part is this lens could almost fit in a watch pocket
thanks again Ole :