Hmmm. I missed the 170mm close-up lens. I thought it wasn't in the
eSIF but see it's considered part and parcel of the 80mm macro and is
only listed there. Its not with the other close-up lenses.
I also overlooked the apo designation. Yes, two elements is achromatic.
It take 3 elements to be apochromatic. Achromats attempt to bring red
and blue (the two ends of the spectrum) to a common focus. Apochromats
do that as well as bringing green (more like the center of the spectrum)
to a common focus. Achromats are common as objectives in refracting
telescopes but the color performance is such that they usually have to
be fairly long focal length and about f/15 to work well. Apochromats
are available for faster lenses... at astronomical prices. :-)
Chuck Norcutt
Moose wrote:
> On 9/3/2010 1:59 PM, usher99@xxxxxxx wrote:
>> I didn't realize the FL of the screw -in diopter. I don't think it
>> is a 2 element apo design. I don't think Dean was thrilled with
>> the results.
>
> Two element. <http://www.angelfire.com/ca/erker/closeups.html>
>
> As it says, though, I believe 2 element is acro, not apo. Not even
> sure if such designations are meaningful in context, as the lenses
> they are put in front of are usually not apochromatic.
>
> I wouldn't mind having one, but have probably not looked very hard.
>
> I have the iS/L Lens A-Macro and B-Macro, but have seldom used them
> what with the true macro lenses lying about.
>
> Moose
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