[pure-silver] Re: Possible optical defect caused by hair or dust within lens?
- From: Helge Nareid <helge@xxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 07 Nov 2009 22:52:32 +0000
Richard Knoppow wrote:
----- 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.
I will in the main agree with Richard on this one. If it only occurs on
a single print or a sequence of images from the same roll, my main
culprit would be a hair between the film and paper in the printing
process. This can best be determined by looking at the negatives. If it
doesn't show on the negatives, it is a printing problem, and simply
reprinting the negatives should eliminate the problem.
The hair (?) showing in the picture of the lens is highly unlikely to be
the problem, since it is likely to be completly out of focus in the
image plane - if the lens were stopped down sufficiently to bring it
into focus, the hair would be well out of the active aperture. It may be
worth checking the relative alignment of the hair and the image artifact.
If the artifact shows up on the negatives - particularly across multiple
rolls of film - my main candidates would be a light leak or an internal
reflection in the optical system. Does this happen with more than one lens?
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