This is the
second apo version 400mm, launched 1988. The
first was released in 1982 and was a 7 elements in 5 groups optical construction (link to pic). This compact 400mm is in size and structure very similar to the optically
much simpler
non-APO 400mm MC version listed here and is the most commonly available sigma 400mm APO. Visually the difference between the AF version (pic 1) and the MF version is the focus barrel which larger on the MF version (most AF ones are for canon, AF ones for pentax are rare/non-existent). Pics 3, 4 show an MF example with OM mount and the "zen" finish from the 1990's, notorious for becoming sticky. This can be cleaned off with eg meths (or alternatively, Dr Kopp in the review linked to below suggests using an automotive compound for restoring aged vinyl). Most of these "APO's" have this zen finish (conversely the non-APO 400's don't).
More importantly than deteriorating paint, these are known to be vulnerable to cemented groups becoming hazed -
avoid, can't be fixed. Pic 5 shows the front objective from a bad one. More commonly it's a speckled hazing of an interior group, pic 6, which, if it's not bad, has only a minimal effect on image quality.
Note the separate listings for the non "apo" 400's, eg
here, and the later 1995 AF version 3 is listed
here.
Description on sigma-imaging-uk.com history pages :
"To minimize the colour aberration, which is the inherent problem of ultra telephoto lens, this lens is using 2 ultra low dispersion glasses in the front lens group. To have high speed AF mode and avoid heavy load to the AF motor, it incorporates inner focusing system. In addition, with a floating lens element system, it will produce high contrast and sharp image in entire focusing range from infinity to closest distance of 4 meters. It is a lightweight, compact, ease to use, high performance ultra APO telephoto lens."
Normally found as PKA mount.
Construction 11 Elements in 8 Groups
Focal Length 400mm
Maximum Aperture ƒ5.6
Minimum Aperture ƒ22
Field of View (24x36) 6°
Minimum Focus Distance 400cm
Number of blades 6
Maximum Magnification 1:9.5
Filter Size 72mm
Diameter 85mm (max.)
Length 213.5mm
Weight 1,100g
Detailed review with crops (nikon) by
Dr Carlo Kopp This web page by Pete Ganzel illustrates disassembly of the lens.
Sigma product development engineer Yasuhiro Ohsone talks about the
development of sigma telephotos including this lens.
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