[pure-silver] Re: Slightly OT: Lens Scratches
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 16 Nov 2004 19:27:04 -0800
----- Original Message -----
From: "Charlie Thorsten" <charlie_thorsten@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, November 16, 2004 7:02 PM
Subject: [pure-silver] Re: Slightly OT: Lens Scratches
> --- Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
>
>> While its often said that scratches on the rear
>> element
>> have more effect than those on the front it really
>> depends
>> on the lens design. I think the idea is that
>> scratches have
>> less effect where the light is less convergent but
>> in
>> practice it makes little difference.
>
> Scratches on the front element can cause flare
> if they catch any sunlight outdoors. It seems
> like scratches on the rear element would be
> inside the bellows and thus not have this problem.
> Of course this doesn't mean they have *NO* affect,
> but hey, just thinking out loud...
>
> In case you couldn't guess, there's a nice lens
> for sale that I'm eyeing. An older "Technika"
> series Schneider 121/8 Super Angulon, with
> "coating marks" on the rear element. Clean
> otherwise, at a good price. I'm tempted...
>
> -Charlie
>
The flare is not from "catching" the sunlight but from
diffraction around the disturbance in the surface. For
example a lens shade will not compensate for the effect of
the scratches. The difference in effect of scratches on the
front from those on a rear element vary with the lens design
but for Tessars they are about the same.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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