Re: APO and IR

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On  9 Dec 96 at 2:43, Vaughan Bromfield wrote:

> >This is also a nice way to qualify the too often used APO: if it 
> >still requires IR-refocus, then its APO qualities are minimal.
> >
> 
> Ahhh sorry to be pedantic, but APO actually has nothing to do with IR. It
> was intended to refer to lenses used to make colour separations for
> printing, where Red, Green and Blue images are created. The high correction
> is required to ensure the rgb images are exactly the same size, otherwise
> the registration of the plates will be poor.
> 
> Now an APO lens may have have a design that happens to imporve the IR
> capability, but strictly speaking it is coincidental and may possibly vary
> between individual lenses.
> 
> Is that why Hassy coined the phrase "super APO" ?

I just adore the fact that Leica APO means that it is IR-focus 
corrected as well. Canon doesn't claim 'L' in general to be 
apochromatic, and the real apo's (containing fluorite) are IR-focus 
corrected. This is a big contrast with Sigma for example, who throws 
in 'APO' on almost any lens, but still requires IR-focus correction.
And I hope you do realize that the only definition of APO is that it 
focuses three colors in a common plane. It doesn't say which colors, 
and it doesn't say with how much precision it must be focused....8-))  
(those who once followed the APO discussions on rec.photo.*, about a 
year ago, with Bob Salomon participating also, know that not even the 
experts use two different definitions)

Besides, it is a nice way to counter all this markedroid speech when 
they start babbling about APO. It's a sure way to get them 
stranded....;-))
And it *does* tell something about lens quality....if Leica sets the 
definition higher than strictly defined, so be it....it's a fuzzy 
definition anyway....







--
Bye,

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      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

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Topic No. 7