[rollei_list] Re: Zeiss Tessar 15cm F4,5 Compur

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <rollei_list@xxxxxxxxxxxxx>
  • Date: Sat, 27 Feb 2010 20:10:23 -0800
----- Original Message ----- From: "Gene Johnson" <genej2ster@xxxxxxxxx> 
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Saturday, February 27, 2010 4:59 PM
Subject: [rollei_list] Re: Zeiss Tessar 15cm F4,5 Compur
Just like Richard says,and it really does make a world of difference. Something really cool about some of these old uncoated lenses. I have a few I just love. But they do tend to get a fog of some sort, and cleaning it off is easy and gets them back to original performance, which in some cases is 
pretty darn good.

Gene
I've found haze on many lenses not just very old ones. some were coated. I don't know what causes it. Its not from lubricant because its on surfaces that are isolated and sealed. I think it may be from the paint used to coat the insides of the cells to make them antii-reflective. Its possible that something remains volitile even though the mounts are proably baked. It could be from the glass itself but I think being coated would affect that. Not all lenses have it. I've found the best way to detect it is simply to shine a flashlight through the lens and look from the other side. Even slight haze will become apparent this way. I've found that even slight haze has a profound effect on lens contrast. I suspect one reason that older, uncoated, lenses are supposed to be high flare is actually due to this haze, although, as I said, its also to be found inside coated lenses. The flashlight trick will also show up faults in cemented surfaces. While we are all familiar with the yellowing ring of oxidized Canada Balsam on old lenses there can also be problems wtih synthetic cements. They can separate into what looks like large bubbles between the elements but also can become hazy. I've found the latter on a couple of Kodak lenses. Under the flashlight test the cement can be seen to have a textured look something like an orange peel. Shining the light obliquely onto the lens surface will also show this up. You may need to use a magnifier to see it. The results, as one would expect, is a serious destruction of lens contrast, even more than caused by the haze. Unfortunately, the only cure for cement problems is to recement the elements. 

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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