Hugo Meyer convertible lens

[zonesys]

Hi,

I got from a family estate a "Hugo Meyer & Co Goerlitz NewYork" (as marked on the shutter) convertible lens. I know the general purpose of a convertible lens... but for this lens I don't know which are the right cells combinations (front + back, front alone, back alone) to set up.

One cell is marked : "Plasmat st 1:45 foc.4 7/16 inch"
Other is double marked : "Plasmat lens 1:8 foc. 6 3/4 inch" and "Plasmat lens 1:11 foc 9 1/16 inch".

Does somebody can help me ?

zonesys

 

[Deckled Edge]

I can't answer all your questions, but two things I know.
1. The shorter, faster element is always the front element when both are attached.
2. When using a single element, it is ALWAYS placed in the rear.

If it came in shutter, there should be at least 3 shutter scales, identified by either maximum aperature or by focal length. This should help with the combinations.

There is a formula available, unknown to me, which dictates what combinations give which (shorter) focal lengths.

 

[Ole]

I can't answer all your questions, but two things I know.
1. The shorter, faster element is always the front element when both are attached....

NO! The shorter element is always placed behind the shutter. When using only one element, think of the air in front as an infinitely long "lens".

The general formula is always 1/F = 1/f1 + 1/f2 + 1/d where F is the combined focal length, f1 and f2 the elements, and d a correction factor which adjusts for spacing and such. The 1/d can usually be ignored.

Putting your information into this equation it doesn't make sense at all, which indicates that the information is incomplete or even wrong. Maybe the lenses are from two different sets?

 

[esearing]

I have a schneider convertable. I can remove the front element (per schneider) and get more focal length but the bellows must be drawn way out. I found that I could remove the rear element and not move the bellows much. The converted greenscale f-stops seem to be about 1 stop off when I use just the front element. I only tested f11-22 however.

Try some tests with polaroids. You may also find the edges are softer than when you combine the two elements.

 

[photobum]

I use the Wollensak not a Meyer, but I have to agree with Ole. Long lens up front.

 

[John Koehrer]

On the HM Plasmat the double marked group is the "front" & single marked group is "rear". Therefore f8 6 3/4" is both groups on shutter and each group used singly will give the other focal lengths marked when mounted on rear of shutter.

 

[Ole]

One cell is marked : "Plasmat st 1:45 foc.4 7/16 inch"
Other is double marked : "Plasmat lens 1:8 foc. 6 3/4 inch" and "Plasmat lens 1:11 foc 9 1/16 inch".

This is what I can't get to add up: Combining a 9 1/16" and a 4 7/8" would give a 3" combined focal length, not 6 3/4". A combination of 9 1/16" and 6 3/4" would be about 3 5/8". To get a 6 3/4" total FL, you'd need to combine the 9 1/16" lens with something around 26 1/2 inch! Knowing a little bit about optics, I very much doubt that Meyer would market a convertible lens with such disparate lens elements. I can think of no example of a combination where one lens is more than twice the length of the other one.

So where does this "1:45 foc.4 7/16 inch" enter into the equation? It just doesn't make sense to me!

 

[sanking]

NO! The shorter element is always placed behind the shutter. When using only one element, think of the air in front as an infinitely long "lens".

The general formula is always 1/F = 1/f1 + 1/f2 + 1/d where F is the combined focal length, f1 and f2 the elements, and d a correction factor which adjusts for spacing and such. The 1/d can usually be ignored.

Putting your information into this equation it doesn't make sense at all, which indicates that the information is incomplete or even wrong. Maybe the lenses are from two different sets?

Perhaps you can help me with the formula. I have a Hugo Meyer Plasmat with a front element of 300 mm and a rear element if 520 mm which I had assume to have a combined focal length of about 300mm, with an aperture of f/6.8 or so. On the camera it is virtually identical in focal lenght to a 12 Dagor. What is the actual focal length of this lens based on the above formula?

Sandy

 

[Ole]

Perhaps you can help me with the formula. I have a Hugo Meyer Plasmat with a front element of 300 mm and a rear element if 520 mm which I had assume to have a combined focal length of about 300mm, with an aperture of f/6.8 or so. On the camera it is virtually identical in focal lenght to a 12 Dagor. What is the actual focal length of this lens based on the above formula?

Sandy

1/(1/520 + 1/300) = 190

Combining a 300mm lens with anything else is unlikely to yield a combined focal length of 300mm - unless the other element has a FL of infinity (0 strength correction element). A 520mm and a 710mm would give 300mm.
Also the shortest focal length is always supposed to be the rear element on all combined lenses - with the exception of tele lenses, where the rear element has negative focal length.

But I will check the published data for Hugo Meyer Satz-Plasmat and Satz-Anastigmat when I get home sometime next week, and post a scan here.

 

[Mark Layne]

I have, among others, a HM Satz Plasmat in Rimset Compur (thus post 1931) marked:
1:4.5 f15.3cm combined
1:11 f32cm front
1:8 f22cm rear

I use this on a 9x12 cm Zeiss Juwel and have a photo on FP4 of the yacht club here with boats anchored near and far and every stay and halyard is clearly defined at 12x16 app. f22

Focus shift is the major problem with convertibles especially single elements and focus must be checked after stopping down. I have never seen a plasmat marked in inches but have some with a simple mm scale and Phil Davis wrote a program for me for Tandy PC6 to do the calculations

Mark

 

[sanking]

1/(1/520 + 1/300) = 190

Combining a 300mm lens with anything else is unlikely to yield a combined focal length of 300mm - unless the other element has a FL of infinity (0 strength correction element). A 520mm and a 710mm would give 300mm.
Also the shortest focal length is always supposed to be the rear element on all combined lenses - with the exception of tele lenses, where the rear element has negative focal length.

But I will check the published data for Hugo Meyer Satz-Plasmat and Satz-Anastigmat when I get home sometime next week, and post a scan here.

Appreciate any help you can provide on the Hugo Meyer plasmat.

On the lens that I have the front element is marked 30 cm 1:5.5 and the rear element 52 cm 1:11. However, both elements are exactly the same size and either could go on the front or back. I am beginning to suspect that Hugo Meyer marked the front element with the combined focal length and the rear one with the focal length of the indiviual element. That would mean, I guess, that what I have is a doppel plasmat, with two elements of 52 cm f/11 that indivually give a 30 cm f/5.5. Does this make sense?

Sandy

 

[Ole]

Makes exellent sense to me, Sandy. Just like the Symmars: Only the rear has "special" marking; in the case of my 240mm the rear is marked 420mm, the front 240/420. So the whole is 240mm, the rear is 420mm, and the front is not supposed to be used alone.

Looks like I'll spend some time with Hans Schmidt's "Photographisches Hilfsbuch für ernste Arbeit" when I get home... It's a great resource for (among other things) information about lenses available in Germany in 1910, the relative merits of the various constructions, and the list price in Berlin!

 

[ongarine]

Sandy,
here some informations that could be usefull for your Meyer Plasmat, taken form a Meyer catalogue of the end of twenties.
Your descrition of the lens is correspondant to:
Double Plasmat f5,5 with rear cell of 20 1/2" front cell 12", has a coverage at full aperture 10x8" and with smallest stop 15x12" with 90 degrees claimed.
You can use the rear cell as landscape lens starting from f11.
No mention for the front cell that for sure will be longer than the rear, it will be around 22" to have, combined with the 20 1/2", a focal length of 12".
I believe you have one scale of aperture on the barrel, so the aperture for the combined set correspond to the double on the single rear cell.
There is another type of Meyer Plasmat called Plasmat set composed of three focal lenghts: front 24 1/2"+back 18 1/2 for a combined of 12" f6,1.
The coverage is the same of the Double Plasmat.
Hope this helps. For further informations let me know.
Daniele

 

[sanking]

Sandy,
here some informations that could be usefull for your Meyer Plasmat, taken form a Meyer catalogue of the end of twenties.
Your descrition of the lens is correspondant to:
Double Plasmat f5,5 with rear cell of 20 1/2" front cell 12", has a coverage at full aperture 10x8" and with smallest stop 15x12" with 90 degrees claimed.
You can use the rear cell as landscape lens starting from f11.
No mention for the front cell that for sure will be longer than the rear, it will be around 22" to have, combined with the 20 1/2", a focal length of 12".
I believe you have one scale of aperture on the barrel, so the aperture for the combined set correspond to the double on the single rear cell.
There is another type of Meyer Plasmat called Plasmat set composed of three focal lenghts: front 24 1/2"+back 18 1/2 for a combined of 12" f6,1.
The coverage is the same of the Double Plasmat.
Hope this helps. For further informations let me know.
Daniele

Thanks for the information. This is very useful.

BTW, does anyone have any advertisements of the period that show the various combinations? If so that would be something great to post up to the forrum as a image file.



Sandy

 

[zonesys]

A lot or informations... and a lot of questions.
To go forward, here is the reply I got on a french large format forum :
(Assuming that "A" is the cell marked 1:4.5 foc 4 7/16" and "B" cell double marked 1:8 foc 6 3/4" & 1:11 foc 9 1/16")
1) "A" alone front : 4 7/16" focal length
2) "B" alone rear : 6 3/4" focal length
3) "A" front + "B" rear = 9 1/16" focal length

What do you think of that ?

zonesys

 

[Ole]

So now I find out that the Plasmat was introduced in 1920, so there's no data in my book... There is a little about them in "a lens collector's vade mecum", which by the way drives me potty since just about eveything is in inches.

Plasmat sets were made in two series:
Series A, f:8, combines to f:4
Series B, f:11, combines to f:5.5

A Series A in back and a Series B in front gave a f:4.5 combination.
Both series were made in a very wide range of focal lengths...

So my best guess is that you have a combination of and A and a B, where the f:11 (B) should be in front.

I think this is about where I give up and suggest you measure the focal lengths of the lenses, then measure the aperture...

A lot or informations... and a lot of questions.
To go forward, here is the reply I got on a french large format forum :
(Assuming that "A" is the cell marked 1:4.5 foc 4 7/16" and "B" cell double marked 1:8 foc 6 3/4" & 1:11 foc 9 1/16")
1) "A" alone front : 4 7/16" focal length
2) "B" alone rear : 6 3/4" focal length
3) "A" front + "B" rear = 9 1/16" focal length

What do you think of that ?

zonesys

I don't think so. There are two ways to add things, and it's important to know the difference: Either "2" + "2" = "4", normal addition. OR: "2" + "2" = "1", since 1/2 + 1/2 = 1. Focal lengths are added as fracton, lens strengths in diopters (as in eyeglasses) are added as numbers. Since the dioptre strength is defined as 1000/F where F is the focal length in millimeters, we see that they are really the same thing. So two 500mm lenses (+2 diopters) will add up to 250mm, or +4 diopters.

Again: Combining two lenses gives a combined focal length shorter than the shortest component.

 

[ongarine]

Dear Zonesys,
the reply you have is a complete mistake.
Your Meyer Plasmat is a f4,5 Plasmat set composed of:
Front lens: 9 1/16" ff11 coverage is enough at smallest stop for almost 8x10
Back lens: 6 5/8" f8 coverage is for 5x7
Combined is: 4 7/16" f4,5 with a coverage for a tight 4x5
I guess you have on barrel or shutter the three scales that allow you to use the correct aperture for each cell or for the two combined. Take note I saw this Plasmat set always in shutter with the appropriate scales.
Easy method to determinated the focal lenght of a convertible is:
FLxFL:FL+FL
FL is focal lenght
Example
front cell 450 rear cell 350 millimetrs
450x350=157500
450+350=800
157500:800=197 millimetrs this is the combined cells
Hope that everything is clear
Daniele

 

[zonesys]

Hi fellows,

Here I post the answer of Seth. Seth is a convertible lenses specialist (check his website www.cameraeccentric.com).

"Hi Jean-Bernard,

This is a "triple convertible" lens. By this I mean, you have three focal lengths to choose from. As you mentioned, the focal length is determined by the combination of cells that are being used on the lens.
By your description of the engraved markings on these lenses you would have the following combinations and effective f stops:

>>4 7/16 " lens at F 4.5 This is with the 9 1/16" cell mounted in the front of the shutter and the 6 3/4" cell mounted in the back of the shutter.

>>6 3/4" lens at F 8 This is with the 9 1/16" cell removed from the
>>front and using only the 6 3/4" cell in the rear.

>>9 1/16" lens at F 11 This is with the 6 3/4" cell removed from the rear and using the 9 1/16" cell in the rear.

The shutter should have the full scale of f stops for each focal length"[/I]

I guess this answer closes my survey... and I'm ready to go on the field.
Does every question poster agree with ?
As said for a wedding ceremony " if anybody have something to say, say it know or remain silent for eternity " !!!

jean-bernard (alias zonesys)
french large format photographer from Toulouse (home of "cassoulet" and "foie gras")

Merry Xmas and Happy NewYear to everybody

 

[Ole]

Merry Christmas to you too, Jean-Bernard! And Jouyeaux Noel!

Everything seems to be right at last.

From Bergen, the home of dried cod