Lee,
At 7:59 PM +0000 8/22/03, olympus-digest wrote:
>Date: Fri, 22 Aug 2003 10:17:05 -0400
>From: "R. Lee Hawkins" <lhawkins@xxxxxxxxxxxxxxxxxxxxxxxxxx>
>Subject: [OM] Re: MC vs SC
>
>Joe Gwinn wrote:
> >Not surprisingly, the more expensive lens (55mm f/1.2) has almost all green
> >reflections, and the same shade of green at that (showing tight process
> >control), while the cheaper lens (50mm f/1.8) has all colors (looser process
> >control) including white (uncoated surface?).
>
>Joe:
>"Process control" has nothing to do with the colors you are seeing, at
>least not in the way you imply. Multicoated lenses typically have a lot
>more colors of reflection than simple single coated lenses. While
>traditionally a single coated lens could be identified by straw colored
>reflections. However, I would guess that the green reflections you see
>in your 55/1.2 are from single coatings that are peaked such that they
>reflect green (although it could be a case of an early, simple
>multicoating prescription).
The implication is that color is useless for telling SC and MC apart. I guess
the only way to really tell is to measure the strength of the reflections,
rather than just eyeballing it, although at least for planar surfaces one can
visually compare reflection strengths with that from an uncoated filter.
With curved surfaces, the spots vary in size and brightness, making visual
comparisons more difficult.
>My guess is that your 50/1.8 is multicoated, and to a much higher
>standard than the 55/1.2.
Based on selling price alone, I would have expected the contrary. The 55/1.2
is a factor more expensive, while the 50/1.8 was the commodity body cap
intended to get Zuikoholoics slightly pregnant.
And the colors of the reflections from the 1.8 were all over the place,
including straw and white.
>As for process control in coating plants, it would be basically useless
>to build a coating plant that performs as you imply. If you couldn't
>control the coating thickness to the wavelength required, it would be
>hard to know what results you would get. The coatings that resulted
>would likely (very likely) end up doing more harm than good.
I believe that too, but what I see is perfect consistency in the 55/1.2 and
complete inconsistency in the 50/1.8, and from economics alone one would expect
more care and tighter tolerances in the more expensive lens.
Joe Gwinn
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