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Re: [OM] The SC MC Debate again

Subject: Re: [OM] The SC MC Debate again
From: "John A. Lind" <jlind@xxxxxxxxxxxx>
Date: Mon, 21 Jan 2002 13:30:22 +0000
At 07:36 1/21/02, Tom Trottier wrote:
On Wednesday, December 05, 2001 at 16:39, ll.clark@xxxxxxxxxxx
<olympus@xxxxxxxxxxxxxxx>
wrote re "Re: [OM] The SC MC Debate again" saying:

> In <4.3.2.7.2.20011204230130.05629b60@xxxxxxxxxxxxxxxxx>, on 12/04/01 at
> 11:27 PM,
>    "John A. Lind" <jlind@xxxxxxxxxxxx> said:
>
> >IMHO, much more ado about SC versus MC is made than the benefit
> >provided by  an MC lens.  There are aspects of the lens design that
> >have a much greater  effect on contrast and flare resistance than going
> >from SC to MC.
>
> Listen, oh brothers, to the clear voice of reason...

Hah!

Yeah, just stick to small-aperture non-retro Tessars like the days before
coating. Forget big (> 3.5) apertures or zooms. Always have the light at
your back, and shoot in the dark. Have a bellows lens hood. That's the way
to avoid flare.

tOM
Tom,
Are you "harvesting" the archives (look at the date of what you quoted)?  :-)

If you were comparing no AR coating to single- or multi-coating I would agree, but not in going from a single-coating to multi-coatings. A single coating does absolute wonders for flare resistance compared to none; the improvement is dramatic. By comparison, changing from a single to a multi-coating formulation only makes a small incremental improvement. Reason? All multi-coatings do is make the effect of AR coating more "broadband" and even across the entire visible spectrum. A properly selected and applied single coating is already fairly broadbanded. I will freely admit this is "per surface" and the reflection (loss) is cumulative. Very complex zoom lenses with fifteen or more elements will suffer transmission loss and flare much more than primes. The loss is multiplicative; i.e. 99% transmission per surface through one surface is 99%, but through ten surfaces it's about 90% (99%^10 = ~90%).
The efficacy of AR coatings (single or multiple) is very dependent on 
coating selection for its index of refraction compared to that of its glass 
substrate (the lens element) and its deposition thickness (based on light 
wavelength).  I don't doubt some lens makers have done a better job of AR 
coating formulation for the specific optical glasses being used.  More than 
one type of glass is used in a lens.  Lens design is not just shape and 
position relative to the other elements/groups, it's also its index of 
refraction.  Furthermore, multi-coatings gain less over single coatings 
when used on higher refractive index optical glass.  A properly chosen 
single coating increases efficacy across the bandwidth of visual spectrum 
as refractive index of the glass substrate is increased.
For those interested in exactly how AR coatings work and the "why" behind 
some of the above, go here and scroll down to the section on "Optical 
Coatings" (about 2/3 of the way down the long page).  Clue:  AR coatings 
are NOT "filters:"
  http://utopia.cord.org/cm/leot/course06_mod08/mod06_08.htm

-- John
P.S.
Don't poke too much fun at the Tessar. It's one of the 20th Century's finest lens designs (almost 19th Century) with elegant simplicity, and is likely the most copied lens formulation ever (after Carl Zeiss' patents ran out at about the end of WWI). Unfortunately it doesn't hold up well in a formulation faster than f/2.8 (aberration), and I probably would not use one for macro "copy" work which requires a very flat field, but how many are using Zuiko's faster than f/2.8 in other than "standard" 50mm lengths?

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