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 :

[Ole Tjugen]

As a rough guide, insert thirds between f:8 and f:11. 8 +1/3 stop = f:9, 8 + 2/3 stop = f:10.

4.5, 6.3, 9, 13, 18, 25, 36, 50, 72, 100 and so on should be familiar to all who use old German lenses - especially as max aperture!

5, 7, 10, 14, 20, 28 and so on is less familiar, but possible on old French lenses.

[Emmanuel BIGLER]

Hello !

The question of determinig the f-number of an old lens has been raised on this forum before.

If you consider that you know the value of the focal length, the diameter to be measured is not the actual diameter of the waterhouse stop itself, but the diameter of the entrance pupil i.e. the diameter of the image of the f-stop as seen from the entrance of the lens through the first lens groups.

f-number = (focal length)/(diameter or the entrance pupil)

It is likely that at the time when this lens was fabricated, people had no idea of the role played by the entrance pupil.
For this unknown old lens, I have no idea whether this can induce a significant difference in the actual f-number with respect to simply taking the measurement of the iris itself.

I had explained in this post how photographers did this measurement one century ago and how you can do it simply today.
http://www.largeformatphotography.info/forum/showthread.php?87304-Copal-3-and-max-aperture-question&p=850369&highlight=pupil#post850369

The quickest way to verifiy the actual value of the focal length of the unknown old lens is to compare on the ground glass the distances between two objects located far away, with a reference lens e.g. a 150 mm : 6" , and the unknown lens. If the lens is a 4" - 100 mm, the distance will be reduced by a factor 1.5. The measurement with a simple ruler can be precise enough to determine both the diameter of the entrance pupil and the focal length.
In fact you only need to know the value with an accuracy of, say, 5% i.e. an error of 5 mm on 100mm, something easily achievable manually with any ruler.

[seawolf66]

Thank you again Ole Tjugen very much



As a rough guide, insert thirds between f:8 and f:11. 8 +1/3 stop = f:9, 8 + 2/3 stop = f:10.

4.5, 6.3, 9, 13, 18, 25, 36, 50, 72, 100 and so on should be familiar to all who use old German lenses - especially as max aperture!

5, 7, 10, 14, 20, 28 and so on is less familiar, but possible on old French lenses.

[seawolf66]

will read over this thread again and the other thread for that information on old lens : Thank you very much



Hello !

The question of determinig the f-number of an old lens has been raised on this forum before.

If you consider that you know the value of the focal length, the diameter to be measured is not the actual diameter of the waterhouse stop itself, but the diameter of the entrance pupil i.e. the diameter of the image of the f-stop as seen from the entrance of the lens through the first lens groups.

f-number = (focal length)/(diameter or the entrance pupil)

It is likely that at the time when this lens was fabricated, people had no idea of the role played by the entrance pupil.
For this unknown old lens, I have no idea whether this can induce a significant difference in the actual f-number with respect to simply taking the measurement of the iris itself.

I had explained in this post how photographers did this measurement one century ago and how you can do it simply today.
http://www.largeformatphotography.info/forum/showthread.php?87304-Copal-3-and-max-aperture-question&p=850369&highlight=pupil#post850369

The quickest way to verifiy the actual value of the focal length of the unknown old lens is to compare on the ground glass the distances between two objects located far away, with a reference lens e.g. a 150 mm : 6" , and the unknown lens. If the lens is a 4" - 100 mm, the distance will be reduced by a factor 1.5. The measurement with a simple ruler can be precise enough to determine both the diameter of the entrance pupil and the focal length.
In fact you only need to know the value with an accuracy of, say, 5% i.e. an error of 5 mm on 100mm, something easily achievable manually with any ruler.

[seawolf66]

And to all others that have commented here I thank you very much

[Emmanuel BIGLER]

I add two references to earlier discussions regarding old engravings & old f-stop systems

one discussion here where Ole gave us the explanations about the old French f-number system
http://www.largeformatphotography.info/forum/showthread.php?26346-Old-Aperture-scape-on-a-Hermagis-lens (http://www.largeformatphotography.info/forum/showthread.php?26346-Old-Aperture-scape-on-a-Hermagis-lens)

and an interesting wikipedia page obout the origins of f-numbers
http://en.wikipedia.org/wiki/F-number#Origins_of_relative_aperture (http://en.wikipedia.org/wiki/F-number#Origins_of_relative_aperture)
where you'll find a scan of an old textbook with a comparative chart of various old F-number systems.

I have merged this info into a single chart; sorry, the (tiny bits of) text are in French, but the chart is self-explanatory. It is part of an article I have written in French about pupils and related formulae.
the old F-number chart in pdf (one page) (http://cjoint.com/12sp/BIcnHlXqf37_annexe-pupilles-tableau-diaphs-anciens-p23.pdf)

And for those who can read French:
The article on pupils in html: http://www.galerie-photo.com/pupilles-objectif-photographie.html (http://www.galerie-photo.com/pupilles-objectif-photographie.html)

Plus a technical annex in pdf : http://www.galerie-photo.com/annexe-pupilles.pdf (http://www.galerie-photo.com/annexe-pupilles.pdf)