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Re: [OM] Slightly OT, Achromatic Macro Lens

Subject: Re: [OM] Slightly OT, Achromatic Macro Lens
From: Moose <olymoose@xxxxxxxxxxxxx>
Date: Sat, 22 Feb 2003 13:12:38 -0800
Simple answer, Sure.

Most close-up lenses that mount on the front of lenses are single element meniscus lenses. The aberration's that they introduce into the resulting image are relatively modest because of their very modest 'power'. They have long focal lengths, so their surfaces are sections of large spheres and spherical aberration is fairly small. It's hard to hold the camera steady enough for sharp close-ups and DOF is poor, so most users looking at 4x6 prints or slides on their old Carousels are simply amazed that they got the close-up shot.

Achromatic close-up lenses are mostly cemented doublets with much better correction of aberrations and will give results superior to the single element versions. Nikon and probably other first line manufacturers make achromatic CU lenses. Oly sidestepped the issue by only making one CU lens of very modest power (the problem escalates fairly quickly with power) for the OM series, the 40 cm fl 49mm and 55mm lenses. They also say in the descriptions " Since the depth of field is extremely small in close-up photography, the lens aperture should be stopped down between F8 and F11 to obtain sharp image definition." What they don't mention is that using a small aperture will also minimize the effect of the CU lens.

Interestingly, Oly later made achromatic CU lenses for the IS series of cameras. Since they are 49 and 55mm, they may be used on any lenses with those filter thread diameters.
A-Macro is a 49mm cemented doublet (2 element, 1 group)
B-Macro is a 55mm air spaced doublet (2 element, 2 group)
A-Life Size Macro is a 49mm air spaced triplet (3 element, 3 group)

None of the above stuff will perform as well as a proper macro lens or the Zuikos with built-in close focus correction. Beyond about +1, CU lenses will generally be inferior to the use of exension tubes.

Wordy Moose

Wayne Harridge wrote:

Dear Zs,

I have just found a "SIGMA ACHROMATIC MACRO LENS" (that's exactly how
its labelled), it appears to be just a close-up diopter lens, looks
about +2, a bit thicker than my other cheap diopters.  Does anyone know
anything about it, whether it is any good ?




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