[rollei_list] Re: xenotar 2.8f vs planar 2.8f

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <rollei_list@xxxxxxxxxxxxx>
  • Date: Wed, 17 May 2006 23:18:47 -0700


----- Original Message ----- From: "Don Williams" <dwilli10@xxxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, May 16, 2006 4:14 PM
Subject: [rollei_list] Re: xenotar 2.8f vs planar 2.8f



At 02:56 PM 5/11/2006 -0700, Jeffery
you wrote:
Richard

I must point out that a lens hood will not make much difference
if the lens is scratched up. The scratches act to diffuse light
from the image. They will, of course, also have an effect on
extra-image light, which is the only light affected by a lens hood.
Scratches affect mostly the contrast of the lens, reducing it
significantly. If bad enough they can also affect the sharpness. I
think its a good rule to avoid scratched lenses. As I pointed out
in an previous post "cleaning marks" are scratches and often very
fine ones. These are quite effective in scattering light and
reducing lens contrast. The term is a euphemism for scratching.
Again, a single large scratch or gough may have minimal effect on
the image where a number of fine scratches will destroy image contrast.


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

There is always one option, when you are far away from civilization
and have just scratched the front surface of a lens. Just paint the
scratch with anything which is opaque, black paint, shoe polish,
whatever. You will lose some light, and depending on the lens
design, you may or may not see some artifact on the image, but you at
least won't have a lot of scattered light which decreases the image contrast.


Just a thought.

DAW

This may help with a few large scratches or if the lens is chipped or gouged. However, fine scratches filled with black paint will still diffuse the light going through in a way similar to stretching black cloth over the lens. Nonetheless, its worth trying.

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


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