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Re: [OM] SC vs MC: The Green Reflection Test

Subject: Re: [OM] SC vs MC: The Green Reflection Test
From: "John A. Lind" <jlind@xxxxxxxxxxx>
Date: Fri, 16 Apr 1999 13:06:55 +0000
At 10:39 4/16/99 , Kelton Rhoads wrote:
>HOWEVER, I have one lens, a 50mm f/1.4, serial number 9001XX, that 
>doesn't support the *reverse* of the hypothesis, which would state, "All 
>MC lenses show a green reflection." (Logicians: isn't this reversed 
>hypothesis called "affirming the consequent"?) The lens I mention is 

Haven't heard that term used for it before . . . but perhaps it is because
of different disciplines studying the same things using different jargon.
There is a difference between "if - then" statements and "if and only if"
statements.

An "if, then" by itself is good only in one direction.  Example:  "If the
air is very smoggy then it is unhealthy to humans."  The reverse is not
necessarily true ("If the air is unhealthy then it is very smoggy").  It is
possible for air to be contaminated with a highly toxic, tasteless,
odorless and colorless gas in which case there will be no smog, but most
certainly the air would be unhealthy to humans.  Another way of stating an
"if, then" is the use of "all [objects of this class or type] have (or do)
posess some other property."  The "if " is the property posessed and the
"then" is the object of the particular class or type.  As stated, the
reverse may be true or untrue.

An "if and only if" statement is good in both directions as it defines an
one-to-one absolute cause and effect in all cases.  So, the question is
whether or not the green reflection is an "if and only if" or an "if, then"
phenomenon.

I have not seen the original statement about the "green reflection" nor
would I want to slight its author.  English is inherently an imprecise
language especially in informal use (such as this mailing list).  This is,
I think, a good question for clarification about the MC and green
reflection rule so we can fully understand and use it accurately.  As
stated in the email prompting my reply the rule appears to be "If green
reflection, then MC lens."  By itself it does not exclude the possibility
of some MC lenses that do not reflect green, but leaves the question open
as to whether any exist.  So, are there some MC lenses that do not reflect
green?

-- John

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