[pure-silver] Re: Possible optical defect caused by hair or dust within lens?
----- Original Message ----- From: "Tom Kershaw" <tom@xxxxxxxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Saturday, November 07, 2009 6:05 AM
Subject: [pure-silver] Possible optical defect caused by hair or dust within lens?
My posting on APUG hasn't generated anything by way of a response, and as there isn't total overlap between pure-silver and APUG I thought I should post here. 

http://www.apug.org/forums/forum40/68152-odd-higher-density-marks-ra-4-print-probably-optical-issue.html

and the image links:
http://www.tomkershaw.com/apug/rf645_65mm_hair.jpg
http://www.tomkershaw.com/apug/strange_mark_kp800.jpg
As the density marks do not appear to be visible in all prints from the RF645 negatives and do not occur with my Bronica SQ negatives, perhaps the hair which is within the lens generates the defect depending on the light direction. 

Tom
I think its very unlikely that the mark is caused by the hair. For one thing, even if the lens design was such that the hair was imaged it would leave a dark mark not a light one. Secondly, in most lenses the hair would not be imaged. I have not explaination for the mark, a hair or thread in the path from lens to film would also have left a dark mark. My best guess is that something happened in processing. I wonder if you have examined the negative. If the mark is _not_ on the negative it suggests that there was some problem with the printer at the lab. BTW, a hair on the inside of a lens is somewhat unusual unless the surface is one that is easily accessed. This looks like its in an air space in the lens mount. Lenses often become hazy on inside surfaces but they are too well sealed for dust and hairs to get there. 

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