I would bet they are single element diopters though the lower power ones as
Chuck mentioned can perform OK.
Mike
I have been using Hoya +1/+2/+4 achromatic sets for decades, and recently I
narrowed it down to just the +1 as I never used the other two. Same for
extension tubes, where I only carry a 10mm. My field filter set is now just
warming (81A and 81B) and cooling (82A and 82B), an ND2, +1 close-up, linear
polariser, and a few adapter rings. Fits nicely in one of those Tamrac filter
wallets.
Never noticed any aberration with the Hoya achromats, but since I've only
used the +1 I might not be experiencing any.
>
>There are several sites summarizing the achromatic diopters available.
>I am slightly puzzled as to why they are not all that readily available
>in lower powers.
>
>I like this site:
>
>http://www.ki.tng.de/~sgude/achromats.html
>
>Not sure where Moose found the Minolta one, but these are not that easy
>to find. I went back and looked at my saved links from a few years ago
>and was impressed that a pixel peeper
>FM'er noted that a well thought of Nykon tele zoom at 200mm performed
>better with the Nykon 5T or 6T or Pentax T132 at infinity focus than
>the zoom alone at MFD--curious.
>
>As Moose is interested largely at 400mm, the extension doesn't look that
>useful or practical, but perhaps at shorter FL's.
>
>Closely revisiting CU lens for upcoming trip, Mike
>
Chris
When the going gets weird, the weird turn pro
- Hunter S. Thompson
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