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Steve T.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 18, 2006 - 08:13 pm: | 
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...without taking it apart? Tessar meaning four elements - two cemented center elements, plus the front and rear single elements.
Lens in question, Vivitar 55mm f2.8 M42 screw mount.
I'm just curious. The lens probably isn't worth much money, whatever the design.
But someone here told me it could be a Tessar clone, and a very good lens (although on the slow side). I saw some sample photos taken with such a lens and they were very nice (maybe the pics were shot with the 55mm f 2.8 Macro lens though - the site didn't say. Mine isn't the macro version, just the "straight" 55mm 2.8). |
charlie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 19, 2006 - 06:43 am: |
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I'm no expert but from threads I have read on line there are Tessars and there are "Tessars". One problem being that the original Tessar formula cannot be made larger than f3.5 and to make a 2.8 "Tessar" the formula had to be modified. Hopefully some one more knowledgable than I can add to this thread |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 19, 2006 - 07:21 am: |
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There is no such thing like the 'original' Tessar formular, except if you refer to the patent application dated 1902. Even the Tessars made by Carl Zeiss Jena (pre-war), Carl Zeiss (post-war western Germany) and Carl Zeiss Jena (post-war east Germany) were modified several times.
However, for 35mm format the lens power never was pushed beyond f/2.8.
You can check whether it's a four-element design (with cemented rear element) by closing the aperture (you have to operate a pin/lever on the lens mount on certain SLR lenses) and take a close look at the rear element, if possible with one single strong small lamp in the room. You will see two rather bright (and big) reflected images of the lamp. If the rear element is cemented you should also be able to see a rather faint and very small reflected image of the lamp.
But there were several different approaches to design 'standard' lenses around f/2.8, some had three rear elements (one cemented and one single), some had a cemented front lens element. The Tessar design is the most common approach. |
Steve T.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 19, 2006 - 01:02 pm: |
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Thanks to you both for the information.
OK, Winfried, if I understand your instructions, I close the aperture and look at the rear element with a bright lamp shining on it.
I saw two side-by-side reflections of the lamp on the rear element. One very bright and right-side up, the other a little more faint and upside-down.
Does that mean Tessar? |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 19, 2006 - 01:20 pm: |
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You should be able to see three reflections. But they will not all be visible from the same direction, you have to swivel the lens around a bit. |
Steve T.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 19, 2006 - 04:15 pm: |
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OK, yes! I do see three. The two I described above, plus one very tiny one in between, which I didn't notice before.
Does that mean it's probably a Tessar design? |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 20, 2006 - 11:58 am: |
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Very probably it is. However there were some Tessar derivates which used more than one cemented element, i.e. a cemented center element, or 'split elements', i.e. they used two separate lens elements in places where the Tessar design uses a single lens element. |
