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Post by John Farrell on Dec 10, 2015 13:51:32 GMT -5
Over the years, I've acquired 4 Zenit E cameras, dating from 1968 to 1980. They all have the same fault with their prisms, a line of corrosion, which can be seen through the viewfinder I have a scrapped Zenit EM, and its prism is the same.
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Post by philbirch on Dec 10, 2015 15:00:32 GMT -5
I had a lot of 6 and all were the same. one or two were almost impossible to focus because the yellowing wal almost covering the screen.
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Stephen
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Still collecting.......
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Post by Stephen on Dec 10, 2015 15:06:54 GMT -5
I have seen this on Russian and other prisms may times, but usually it does not show in normal use with the eye in the usual position. A well finished prism edge will all but be invisible, but the line is still there, as you cannot grind the glass to the very edge, usually about 5 microns off on an average edge, but finer on very high quality items. I expect the Russian standard was lower to start with, and the edge shows because dirt has got on the minute un-ground area at the tip edge of the prism.
In normal use the eye is not focused on the interior of the prism, it is meant to be exactly focused on the ground glass focusing screen.
Therefore the prism edges are well outside the focus point of the eye, and the blurring helps give a smooth view. The same applies to the roof prism binocular.
When a view from outside the camera is taken, as in your shot, it is focusing short of the screen, inside the prism itself, and any bad edge will show up as you have found.
Generally the standards of grinding in the USSR were the same as any producer, after all they out produced everybody else! But as usual they had no reason to be better, except for the sake of it, and lower standards slipped into the ways of production, just good enough to be usable.
Old Edixa prisms have the same lines, and I have seen makes with blotches in the view due to using glue on the prism to fit packing, the glue attacks the glass surface.
Stephen.
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Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
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Post by Stephen on Dec 10, 2015 15:23:57 GMT -5
The picture shows the line that shows in a traditional pentaprism. It is about 2.5cm short of the screen, and should be out of focus to the viewing eye. The line may not appear in digital camera with prisms as they use non reversing designs with no ridge, achieving the reverse digitally, and using the front surface to allow a sensor to view direct. But Film cameras always have a reversing Prism, unless very vintage designs like the Wray, or a porroviewer like the Olympus Pen and the Gamma. Stephen.
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Post by camfiend on Dec 10, 2015 22:47:39 GMT -5
very strange, I have the same thing on my Zenit E.. also have two Zenit EMs both have the same fault
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Post by John Farrell on Dec 11, 2015 0:53:35 GMT -5
I took the photograph with the lens removed. The line is quite obvious when the cameras are used with a lens. Oddly enough, I have a Zenit 3M which doesn't have the line, and a Zenit B which is just starting to show it.
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Post by camfiend on Dec 11, 2015 3:13:11 GMT -5
maybe I just got the lucky door prize with the EMs... I have more than a dozen other Zenits including an E Global which seem fine
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Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
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Post by Stephen on Dec 11, 2015 5:15:53 GMT -5
If it is progressive, getting worse with age, then the silvering is breaking down at the edge as the protective paint is thinner over the crown edge of the Pentaprism. the damage can't be halted, it is the silver breaking down to oxide.
Stephen
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Post by yashica1943 on Dec 11, 2015 9:45:10 GMT -5
I have a Konica FP- 1 with the same effect.
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