Younger Jupiter-8(M) not a classic Sonnar anymore?

ForenSeil · Joined: 15 Apr 2011 Posts: 2726 Location: Kiel, Germany.

I've disassembled a 1973 Jupiter-8M 50/2 an noticed that the rear element is very different from what I've expected (first two or looking more or less like supposed)

It seems to be not the classic Sonnar design the (old) Jupiter-8 is supposed to be

That would partially explain the "quality spreading" we were all talking about so often Very Happy

themoleman342 · Expire: 2013-01-24

I asked something about the designs a few months ago: http://forum.mflenses.com/jupiter-8-and-8m-t46646,highlight,+jupiter++8m.html
Maybe something can be taken from that?

ForenSeil · Joined: 15 Apr 2011 Posts: 2726 Location: Kiel, Germany.

sichko · Joined: 20 Jun 2008 Posts: 2475 Location: South West UK

If you look at the Bertele/Zeiss patents there are several examples of what might be described as "Sonnar designs" which have a slighty concave face in the position indicated in your photo.

fermy · Joined: 17 Feb 2012 Posts: 1974

Here's what fedka has to say

iangreenhalgh1 · Expire: 2014-01-07

Of course it's a Sonnar, your photo of the optics shows you clearly have a front single element, then a cemented triplet then a cemented doublet. How can you tell the curvature of the front element of the rear doublet from the low res crude images of the design on the web?

Also, GOI recalculated the Sonnar to make the J8 to account for different Russian glass types, the curvature of the element could have been changed slightly, but this doesn't mean it isn't a Sonnar, just a slightly recalculated one. Maybe they recalculated it again when they made the M version, wouldn't surprise me as the 8M I tried was noticeably less sharp than my three J8s.

This 'quality spreading' some people insist exists in Russian lenses is probably largely mythical, and rooted in the condition of various examples, a good condition one outperforming one with issues. Personally, out of at least 30 copies, I've yet to find a less than great Russian lens.

themoleman342 · Expire: 2013-01-24

iangreenhalgh1 · Expire: 2014-01-07

fermy · Joined: 17 Feb 2012 Posts: 1974

Let's not go poetic about Soviet quality. As someone who lived in Soviet Union, I can tell you that significant quality variation in all consumer products was a fact of daily life. That has nothing to do with any psychological perception of cheapness. It's also hard to tell what is cheap. J-9 cost 40 rubles, exactly 1/3 of a monthly salary of an engineer. That is probably more expensive than what similar lens cost in the west compared to salary.

And yes, unless one is talking about coke bottles that were designed to be crap and carefully assembled to be crap, individual condition of any vintage lens will play a bigger role than the make, here I completely agree.

iangreenhalgh1 · Expire: 2014-01-07

I'm not trying to be poetic about Soviet quality, I'm just saying experience suggests bad ones are less common than popular myth suggests.

When I mentioned the difference in economics I was thinking of how the Soviet lens producers were only small appendages of vast military/industrial complexes. KMZ, for example, was a vast plant and the camera lens production lines are only a small part of it, therefore compared to the military optical production, the consumer part was fairly insignificant in the grand economic scheme of things.

That contrasts quite sharply to the west where companies like Canon and Pentax are camera companies first and foremost.

ForenSeil · Joined: 15 Apr 2011 Posts: 2726 Location: Kiel, Germany.

Orio · Expire: 2012-12-04

I have found bad soviet lens copies -more bad Jenas than Russian, to be honest- but I am inclined to believe that they had to do more with misuse or improper cleaning/reassembling than with actual poor production.
It is true, however, that soviet lenses from the 70s until the fall of the regimes in 1989, did use bad quality materials, especially with regards to mechanical parts.
All and I mean ALL Jena lenses from the 70s onwards, except just ONE (the last MC Sonnar 2.8/180 that I am keeping), have had mechanical failures
to aperture system that forced me to take them to lens servicing one time or another.
With Russian, this wasn't so bad, but indeed the materials in some of the latest Helios-44, for instance, are really near to crap (but always better than $2000+ Canon plastics anyway Laughing

)

About the rear element... difficult to tell from your picture's frontal angle... if you could show a lateral image maybe.

ForenSeil · Joined: 15 Apr 2011 Posts: 2726 Location: Kiel, Germany.

Orio · Expire: 2012-12-04

I'm sorry, then an oblique image would work perhaps
all I can see from the current image, is the black barrel's casing. Sad

ForenSeil · Joined: 15 Apr 2011 Posts: 2726 Location: Kiel, Germany.

Orio · Expire: 2012-12-04

Ok, thanks for trying, but I give up. It's too difficult to see the shape of a transparent object.
Anyway it's an interesting finding, it would be cool to know what an optical engineer thinks of this.

iangreenhalgh1 · Expire: 2014-01-07

The optical diagrams you are looking at are very low res web graphics, therefore you have no idea what the curvature of that surface should actually be, and will get no idea from looking at these type of diagrams, you need to find one that tells you the actual curvatures and design specs, not just a simple line illustration. Until you determine the actual curves of the Sonanr 2/50 design, this is all just pointless speculation.

That surface probably should be concave, the Nikkor copy of the Sonnar has a concave surface in that position:

The 1.5/50 Sonnar has a rear group looking very like the one Forenseil has:

But this is all pointless speculation until someone finds the correct optical diagram with the correct curvatures indicated. Maybe Marco Cavina has one?

I haven't found one on Marco's site, but you need to find one like this with the actual curve radii:

This one for a larger Sonnar also shows a concave surface at the front of the rear group:

On this diagram, Marco shows the Sonnar 2/50 with a concave surface at the front of the rear group:

The two later recalculations of the lens are also shown to have concave surfaces there:

So really, what this thread boils down to is someone compared reality to a tiny web graphic and got confused, a little research would have solved this, speculation about the Russians changing things doesn't help.

iangreenhalgh1 · Expire: 2014-01-07

I think I found the correct data sheet for the 2/50 Sonnar:

Looks like the J8 parts Forenseil showed to me, with the rear group having a taper and a concave front surface.

The Postwar recalculation to use modern glasses shows the same concave surface and also a taper to the rear group:

Another recalculation with a concave surface:

So can we conclude that there is nothing unusual about a J8 having a concave surface on the front of it's rear group?

Marco shows this diagram for the J8:

visualopsins · Expire: 2025-04-11

Thanks for lens diagrams!!! Recently bought Jupiter 8M 2/50 for Kiev/Contax RF for $12 and Contax/Kiev RF to Nex helicoid adapter for $30. Did I get a nice Sonnar for $42? Smile