Voigtländer Euryscop V focal lenght?

[matti]

I have been through Vademecum and searched here and come up with a lot of info - that didn't really make me sure to what focal lenght/coverage/f-stop I can expect of this lens.

It is a Voigtländer & Sohn. Braunschweig Rapid Weitwinkel Euryscop V at size No 2. Serial # is 45900.

Obviously it is an aplanat and I found (there was a url link here which no longer exists) that Ole posted here. But this is for series VI

In this post at the LF-forum it says:

The " Fifth Series Rapid Wide-Angle Euryscope F6 Angle 80 degrees, size marked 0 to 5 with special Jena Glass.

So, would my size 2 be the same as Oles 2a which is 13 inches but F6 instead of F8 with wider coverage?

Maybe I should just learn how to measure these things myself...

/matti

 

[gandolfi]

point your lens at the sun (or something in infinitive) - mesure the length from the aperture scale to where it focuses.....(30cm distance is 300mm focal length)

focal length (as I have been taught)

PS: I was looking at a HUGE euryscop (nr8 which isnt in the Vade Mecum) in Pragh...

they wouldn't let me take it out to mesure the focal length, so I didn't buy it..

however, I am going to Prague again this spring, and IF it is still there, it must me a sign from above...
(quite pricy, though..)

 

[matti]

Thanks Emil, I will try that. It is the waterstop-opening where the apertures go that one measures from, no?

PS
Since nr 7 is 710 mm in Oles list the nr 8 might have been 910 mm. Sounds like a lot of glass.

/matti

 

[JBrunner]

Yeah, you are looking for the nodal point. If you are off a little bit, thats how far you will be off, but you will get at least a good approximation of FL.

To get a rough aproximation of stop, divide the diameter of the objective into the FL, using the same units.

For example FL=8inch & D=2inch indicates f4

works for all units, as long as you stick within that system.

 

[matti]

Thank you Jason, that is about everything I need to know. At last I understand how easy this is. I especially like this sentence: "If you are off a little bit, thats how far you will be off." It actually made me understand what focal length really means. Time for a new video?

/matti

Yeah, you are looking for the nodal point. If you are off a little bit, thats how far you will be off, but you will get at least a good approximation of FL.

To get a rough aproximation of stop, divide the diameter of the objective into the FL, using the same units.

For example FL=8inch & D=2inch indicates f4

works for all units, as long as you stick within that system.

 

[Ole]

Serie V no. 2 is an 11".

 

[matti]

Thanks Ole 280 mm then. Odd that they didn't stick to the same size numbers between the series.

/matti

 

[Ole]

There are - well, "reasons" for changing the numbers:

Sometimes the numbers denote focal length, sometimes intended plate size. These tend to be similar for normal lenses, but with "oddballs" like extra-rapid wideangle aplanats, there aren't really any "standards.

No. 2 will often denote 13x18cm plate size, or about 210mm focal length. In the specific case of the Serie V, the lens has less (sharpish) coverage wide open than a normal f:7.2 Aplanat/Euryskop, but gaing wider coverage than normals on stopping down. So the "numbering" is done on the basis of coverage wide open, which is about the same as that of a 210mm f:7.2 "standard Aplanat".

At least that seems to make sense to me, comparing dozens of different "Series" and numberings from dozens of manufacturers.