Is this a blemish or not?

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Waltzing Paul
Posts: 49
Joined: 16 May 2013, 21:11
Location: Brisbane, Qld

Is this a blemish or not?

Postby Waltzing Paul » 25 Aug 2013, 18:54

I recently aquired a used lens which has a rather interesting blemish.
It's a 240mm Linhof lens by Schneider Kreutznach and is in very good condition.
I took some polaroid photos to see if the blemish has an effect on the picture quality.
They came out very good with no sign of any issues although I couldn't produce a large image to see the fine detail.
The blemish is about 2mm in diameter and is within the glass (not on the surface).
You can only see it in certain light by angling the lens.
Looking straight through the lens it is virtually invisible.
Can anyone shed any light on this?

Lens 3 small.jpg
Lens 3 small.jpg (295 KiB) Viewed 1639 times

Lens 1 small.jpg
Lens 1 small.jpg (224.88 KiB) Viewed 1639 times
Paul

The pictures you want tomorrow, you have to take today". - Anonymous - Kodak advertisement

Andrew Nichols
Posts: 181
Joined: 11 Dec 2012, 17:19

Re: Is this a blemish or not?

Postby Andrew Nichols » 25 Aug 2013, 19:05

often air bubbles and such are ok, as they some how dont effect image.
it has to be a big blemish to cause an effect.
i have an air bubble and a chip of 1mm no probs
sorry i cant give you a technical reason.

Geoff Roberts
Posts: 109
Joined: 29 Jul 2012, 22:03
Location: Sydney
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Re: Is this a blemish or not?

Postby Geoff Roberts » 25 Aug 2013, 20:37

I have never seen anything like that before, no idea what it is. If you're happy with the pictures I wouldn't worry, unless it's something that can deteriorate over time.

Lachlan717
Posts: 495
Joined: 03 Aug 2012, 16:49

Re: Is this a blemish or not?

Postby Lachlan717 » 26 Aug 2013, 06:45

"Perfect" glass is a relatively modern concept in photography. It seems to coincide with multicoating.

As Andrew wrote, it takes a pretty substantial issue to show up in the image. I recall seeing a website quite a few years ago where a cracked (35mm) lens was tested. http://kurtmunger.com/dirty_lens_articleid35.html
So, I wouldn't worry a out this.

And, sometimes it can work in your favour: I bought a 14" Verito that has 3 tiny chips in the rear glass for $150. It's a soft focus lens FFS.

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Maris
Posts: 590
Joined: 27 Jul 2012, 16:02
Location: Noosa

Re: Is this a blemish or not?

Postby Maris » 26 Aug 2013, 11:01

Yes that is a blemish It's a failure in the interlens cement causing a lens element separation at that point. The separation may stay small or it might grow (over years or decades) causing the lens elements to separate completely. Only time will tell.

While the separation is small it's virtually impossible to find a degradation in image quality. One thing for sure, the resale price of such a lens drops dramatically. When I'm buying used lenses I look for flaws like this to cadge a great lens at a bargain price.


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