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So I got this from a 2nd hand site... (Porst 55/1.2)
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PostPosted: Sat Dec 19, 2009 7:12 pm    Post subject: Reply with quote
Phoenix thank you for your samples. I am eager to see more. Well i'll also do it myself when the cold goes away. This samples are probably not post-processed and as such pretty interesting.


PostPosted: Sun Dec 20, 2009 10:42 am    Post subject: Reply with quote
Phenix jc wrote:
The Porst 55/1.2 is known to be a 6 lenses formula (There is 2 versions of this lens, f16/f22, 0.5/0.6m, but with a F, we can consider this for sure).
http://kamera-geschichte.de/files/porst_slr_compact_reflex_oc.htm
Consensus on the fact it isn't a M42 Tomioka like.

I presume the info about 6 elements comes from the single Porst booklet, which was already mentioned here. There is no other source, which would confirm that. There's no optical scheme, too.

Not even the cheapest 50/1.4 lenses were based on 6 elements only. Even the simpliest 50/1.2 lenses have 7 or more elements.

Notice, that the porst 50/1.4 lens has 7 elements. There's no sense to use 6 elements for f/1.2 lens.

Anyway, optical performance is identical to Tomioka 55/1.2 and even number, shape and position of reflections is identical to the old Tomioka. If you look at the Tomioka optical scheme, you can notice, that shape of lenses in rear optical block is very unique - both surfaces of the cemented doublet are concave(!) All other fast 50mm lenses based on this optical formula have concave-convex doublet (like typical achromatic meniscus).

It's almost impossible, that two lenses, which has the same number of reflections (= the same number of otical elements) and identically shaped reflections (= identically shaped optical elements) are in fact two different designs coming from two different manufacturers using different number of optical elements Confused

there are 2 reasons to think the lens has 6 elements:
1. Porst booklet
2. letter "F"

there are 5 reasons to think the lens doesn't have 6 elements:
1. 6 elements are simply too little for f/1.2 double-gauss design
2. it doesn't make any sense to use 7 elements for f/1.4 lens, but only 6 el. for (way more expensive) f/1.2 lens
3. number of reflections points at 7 elements (1-1-1|2-1-1)
4. shape of reflections and overall optical performance/character/aberrations are identical to Tomioka 55/1.2, which has 7 elements
5. length of Tomioka 55/1.2 optical block is 53mm, length of Porst 55/1.2 optical block is 53mm

Smile

//edit: Porst 28/2.8 M42 has "N" letter written on the ring. It's highly unlikely, that the lens would be based on twice as many (14) optical elements, than other contemporary 28/2.8 lenses (7-8 elements typically).


PostPosted: Sun Dec 20, 2009 11:07 am    Post subject: Reply with quote
Well, it looks as if somebody will have to disassmble the lens to get a final verdict Laughing


PostPosted: Sun Dec 20, 2009 12:01 pm    Post subject: Reply with quote
I think the original intention was to mark number of optical elements by that letters, but there are likely some errors. It could be a result of misunderstanding due to language barrier. Porst is German brand, while many of the lenses were made in Japan. I think sense of phrases like "number of optical groups" and "number of optical elements" was confused.

That would explain "F" in Porst 55/1.2 - it has 7 optical elements, BUT 6 optical groups.

If you look at old optical patents, some German inventors used words "element", "member" and "component" for the thing which we call "group" now, while other of them (and many Japanese inventors) uses these words for the thing we call "element" now. So nomenclature - esp. translated, was really confusing then.

e.g. Lange (Zeiss Oberkochen, he computed the Oberkochen version of Tessar) decribes Tessar (1-1|2) as an objective with 3 elements(!), where the 3rd element consists of two cemented lenses. While e.g. Glatzel used word "element" as we use it now.


"N" in Porst 28/2.8 is harder to explain, but the lens has very likely 14 optical surfaces - again, it could be just a misunderstanding. I'd take into account, that Porst was just a brand and its workers weren't optical experts, but businessmen and marketing experts.


PostPosted: Sun Dec 20, 2009 12:22 pm    Post subject: Reply with quote
C'mon Smile get your tools out and disassemble it!!! Twisted Evil

I will keep my eye on the listings @theBay if there's some defective/fungued one for 10 bucks or so for that sake ...


PostPosted: Sun Dec 20, 2009 12:59 pm    Post subject: Reply with quote
It's not necessary to disassemble it. Flash-light test is reliable. Strong color reflections = coated (air/glass) surfaces; weak white reflections = uncoated (cemented) surfaces.

The lens has 6 color reflections in the front group (= 3 separated lens elements) and 6 color + 1 white reflection in the rear group (= 4 lens elements, 2 of them cemented into a single doublet) = 7/6 (1-1-1|2-1-1) design.

I think the person who don't believe, that the lens is 7/6 formula, should disassemble it. I'm sure it is Wink


PostPosted: Sun Dec 20, 2009 11:20 pm    Post subject: Reply with quote
Pancolart wrote:
Phoenix thank you for your samples. I am eager to see more. Well i'll also do it myself when the cold goes away. This samples are probably not post-processed and as such pretty interesting.

No post-processing, and wide open
(sorry, i'll change my signature)


PostPosted: Mon Dec 21, 2009 12:22 am    Post subject: Reply with quote
no-X, I don't have such an expertise level, my knowledge only comes from the web, and it seems you have a lonely position on this issue, but perhaps the good one ; As you wrote, you have both these lenses :
no-X wrote:
Sorry, but this info is incorrect. I have both these lenses - Tomioka Yashinon 55/1.2 and Porst MC 55/1.2.

Both of them has 55mm filter thread. Both of them have 7 optical elements. And it's very likely exactly the same optical design - inner reflections are identical - number of them, shape, size and even position. Even their performance is identical - bokeh, sharpness, etc. The only difference is color rendition, the coating is very different.

f/1.2 double-guass lenses are based at least on 7 optical elements.

So I must add, that, in my opinion, the samples of photographs I've seen showed 2 differents characters, but it's very uneasy to compare ;
Is it possible to have from you some pictures of a same subject taken with this 2 lenses ? Wink


PostPosted: Sat Oct 02, 2010 7:28 pm    Post subject: Reply with quote
http://forum.mflenses.com/tomioka-zeiss-mamiya-and-55-1-4-design-t22661,start,15.html#214489

http://forum.mflenses.com/overview-55mm-f1-2-lenses-t32769.html#1072734

Yes, no-X, I was knowing Gabriel on a french forum when he opened the Porst, so I knew already at that time that you were right

The fact that there is not a single 50/55mm f1.2 without a minimum of 7 elements was a strong argument.

I was looking after this Tomioka/Porst problems since 2008 on the web, and, perhaps it's a good thing to note, that, as time passes, knowledge improves
(I hope my english is understandable)


PostPosted: Sat Oct 02, 2010 8:10 pm    Post subject: Reply with quote
As for different character - there is really huge difference in color cast. The reason is coating (porst's coating is blueish, tomioka's coating is gold). Tomioka's results can be affected by browned thorium element. Porst doesn't have it, I think it was replaced by some modern glass material, which has similar optical qualities without any radioactivity.
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