Isco Verlängerungslinse 13,5/25,5 exposure compensation?

[JPD]

I have this Isco Verlängerungslinse accessory lens that increases the focal length from 13,5 to 25,5 cm. It's equivalent to the Zeiss Distar. It requires some exposure compensation, but how much? Let's say at a normal head and shoulder portrait distance. ½ or 1 stop?

 

[Dustin McAmera]

Naively, it seems you're doubling the focal length, so what's marked as f/8 is now f/16; two stops?

 

[JPD]

Naively, it seems you're doubling the focal length, so what's marked as f/8 is now f/16; two stops?

Yes, something like that, probably. Doubling the focal length and a lot of bellows draw. I should experiment.

 

[Dan Fromm]

Hmm. I thought that afocal adapters mounted in front of a lens don't change the f/ number.

 

[Doremus Scudder]

Hmm. I thought that afocal adapters mounted in front of a lens don't change the f/ number.

+1

 

[JPD]

Hmm. I thought that afocal adapters mounted in front of a lens don't change the f/ number.

+1

Well, according to Willy Frerk in Lichtbildkunde, Band 1:

 

[Dan Fromm]

Patric, although I lived in Germany for a year and played in my town's orchestra, I never learned German. Well, enough musical German to follow our conductor.

Please translate and summarize.

 

[JPD]

Patric, although I lived in Germany for a year and played in my town's orchestra, I never learned German. Well, enough musical German to follow our conductor.

Please translate and summarize.

The Google Translate smartphone app is handy:

 

[Dustin McAmera]

I have some Agfa Verlängerungslinsen, which fit my 9x12 Standard (I have hardly usedthe camera, and never the lenses). They are described on page 19 of this (German - sorry) catalogue reproduced at Pacific Rim Camera:
https://www.pacificrimcamera.com/rl/02375/02375.pdf (PDF, about 59MB)

Google translates that page as

The Agfa extension lenses are manufactured in 2 types, type A for 1.3x focal length extension, type B for 1.5x. The image magnification corresponds to the focal length extension. For better depth of field, it is recommended to stop down slightly, especially for landscapes, while for portraits where pin sharpness is not a priority, you can work without stopping down. The aperture numbers of the lens are no longer decisive. The exposure is extended by 1.7 times for type A, and by 2 times for type B.
Agfa extension lens type A ........ RM.4.95
Agfa extension lens type B .........RM.4.95


An extension of 1.3x hardly seems worth bothering with.

(edited: it is 1.7 times for type A, not 7 times, clearly)

 

[JPD]

I have some Agfa Verlängerungslinsen, which fit my 9x12 Standard (I have hardly usedthe camera, and never the lenses). They are described on page 19 of this (German - sorry) catalogue reproduced at Pacific Rim Camera:
https://www.pacificrimcamera.com/rl/02375/02375.pdf (PDF, about 59MB)

Google translates that page as

The Agfa extension lenses are manufactured in 2 types, type A for 1.3x focal length extension, type B for 1.5x. The image magnification corresponds to the focal length extension. For better depth of field, it is recommended to stop down slightly, especially for landscapes, while for portraits where pin sharpness is not a priority, you can work without stopping down. The aperture numbers of the lens are no longer decisive. The exposure is extended by 7 times for type A, and by 2 times for type B.
Agfa extension lens type A ........ RM.4.95
Agfa extension lens type B .........RM.4.95


An extension of 1.3x hardly seems worth bothering with.

Thanks, I have seen a couple of the Agfa Verlängerungslinsen, but only the 13,5/16,5 version, and wouldn't that be only 1,2x? It would work for head and shoulder portraits, but the 1,5x would of course be better. I don't like the mount Agfa used as you would need filters and hood of a larger diameter to fit on top of it, or maybe one of those old filter holders you clamp on with leaf springs.

And the Zeiss Distar lenses and their codes for the diameters. You have to remember that "Coa" means 30mm, "Co*" means 28,5mm and "III" means 37mm. "2/III" would be the perfect portrait attachment for my 13,5cm Heliar.

I have a RÜO Iricentor 6,8/18cm, a very good dagor clone according to Willy Frerk, and the perfect focal length for 9x12 portraits, but the retaining ring is stuck like it's welded on, so I can't mount it on a camera.

 

[reddesert]

This thingy is presumably, like the Zeiss Distars, Proxars, and ordinary closeup lenses, a simple lens, in this case it should be a concave, diverging lens. It's not afocal - an afocal lens has no net power, like the cheapo screw-in front mount converters you can get for video cameras, or the close-up and tele attachments sold for 1960s TLRs and rangefinders. That's why those don't require exposure compensation, but this one does, at least in theory.

 

[JPD]

This thingy is presumably, like the Zeiss Distars, Proxars, and ordinary closeup lenses, a simple lens, in this case it should be a concave, diverging lens. It's not afocal - an afocal lens has no net power, like the cheapo screw-in front mount converters you can get for video cameras, or the close-up and tele attachments sold for 1960s TLRs and rangefinders. That's why those don't require exposure compensation, but this one does, at least in theory.

Maybe Dan and Doremus misunderstood something. It's indeed just a simple negative meniscus, like the Distar, for fixed lens plate cameras. The one I have almost doubles the focal length.

 

[JensH]

Hi JPD,

what about an empirical approach:
Take a handheld meter and measure how much light gets to the image plane with the lens attached and without it.

Best
Jens

 

[JPD]

Hi JPD,

what about an empirical approach:
Take a handheld meter and measure how much light gets to the image plane with the lens attached and without it.

Best
Jens

When focused at infinity. Good idea, I'll do that later this week when I have access to my tripod and light meter. And take test shots to see how it behaves.

 

[JensH]

... one more literature based guess: (nearly) 2 Stops.

Windisch (Die neue Photo-Schule, 1943, p. 176) gives:

Extended focal lengh..............Exposure
1.5x......................2x
1.75x....................3x
2.0x......................4x

Greetings
Jens

 

[JPD]

... one more literature based guess: (nearly) 2 Stops.

Windisch (Die neue Photo-Schule, 1943, p. 176) gives:

Extended focal lengh..............Exposure
1.5x......................2x
1.75x....................3x
2.0x......................4x

Greetings
Jens

Right. I'll go by that, but also do the light meter test. I have that book by Windisch somewhere. Is it the one that came in three parts? Maybe that depends on the edition.

 

[JensH]

Right. I'll go by that, but also do the light meter test. I have that book by Windisch somewhere. Is it the one that came in three parts? Maybe that depends on the edition.

Hej again,

no, my edition is just a single book, 255 pages.
No references/advertisements to other parts inside of the book.

Maybe there have been extended editions after war?

Jens

 

[JPD]

Hej again,

no, my edition is just a single book, 255 pages.
No references/advertisements to other parts inside of the book.

Maybe there have been extended editions after war?

Jens

Hej,

I couldn't find it and assumed it was the set of three books that I put in the attic because they smelled of mildew, but I was wrong and those books were "Knipse - aber richtig!" by Wolf H. Döring, another "photo school". I do have the Windisch book somewhere.

I'm sneezing from dust and old books, looking for a book by Jenö Dulovits printed in 1949 I'm sure I have but can't find. Bad book luck today, no order, and I who used to work in a library...

 

[Doremus Scudder]

Well, it seems the lenses in question do change the effective aperture, and therefore either require that one calculates the new aperture and bases exposure on that or uses an exposure compensation.

I stand corrected - for the second time today. Two new things learned!

Best,

Doremus