Re: HIE and Leica M

["Anthony W. Maw" <amaw@xxxxxxxxx>]

Yes. I think the percentage theory is correct.  The underlying principle is
that the refractive index of a substance (such as optical glass) varies with
the wavelength of the radiation passing through it, notwithstanding atomic
and molecular absorbencies.

This is a lame excuse for not being more precise but although I still have
my advanced physics textbooks from my college days.....


- -----Original Message-----
From: Larry Bullis <lbullis@xxxxxxxxxxx>
To: infrared@xxxxx <infrared@xxxxx>
Date: Wednesday, January 07, 1998 1:09 PM
Subject: Re: HIE and Leica M


>
>
>
>> > You may notice that there is no infrared mark on your Leica lenses.
>[.....]
>
>>
>> The 'not doing things half-way' theory is correct, but not like you
>> said. It is claimed that Leica found the IR-focus indicator useless,
>> as it applies to infinity focus only....nearby the error is different
>> (I don't know in which direction....anyone?).
>>
>Well, it would have to be longer and longer.  It seems that it works by a
>percentage; in other words, the ir focus makes a slightly longer lens of
>it for ir than for visible light.  I don't remember the percentage
>increase in extension Kodak suggests, but if you apply that extension to
>the nearer (extended) focus, it would always be longer.
>
>Thanks for clearing this up.  Very interesting.
>
>Larry Bullis
>Skagit Valley College
>(but now in Tacoma, for whatever that's worth!)
>
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