These days i'm using a great 180mm.
It sat for long time in a drawer, cause it was not the best focal for APS-C, and was too slow for low light use.
It is the Sigma Apo Macro 5.6/180mm. It was released in 1993, and was later made in AF mount too.
AFAIK the Pentax version was sold in MF version only.
On my K-1 is proving to be exceptional.
Only one limit: speed. Only one defect: the "Zen finish" has become goo-ish close to the diaphragm ring, where i used to hold the lens between my fingers (to support the camera or mount/unmount the objective).
Probably the last time i used it (in the woods) my sweat was acidic, or my fingers got in contact with some stuff that later attacked the non-slip, matte finish that protects the barrel. Sigma used it for a certain time, i remember.
The problem is not unknown, many Zen finish lenses are showing this kind of decay of the rubber coating.
If anyone has found a way to fix/harden the surface, making it less sticky without also removing the silkscreened markings, it would be a great information. Sharing it would help others in the same situation.
Fortunately my lens is not a mess, just a little sticky close to the diaphragm ring, while the rubber of the focusing ring is still fine.
All in all the problem is more psychological than practical... but it's a good reminder to always wipe the lens with a microfiber cloth after use, if it will be stored for some time!
Optically the lens is simply amazing, considering its age:
- sharp wide open, VERY sharp at f/8
- no CA at all, even in high contrast areas
- nice bokeh
In my experience, not all macros have a nice OOF rendition. For example, my Sigma EX DG Macro 2.8/50mm has a terrible bokeh, in my opinion.
The lens is very small for its focal, and very ergonomic to use (it's a PKA).
The only limitations are the macro range (1:2) and the speed (f/5.6).
It's an uncommon lens, but if you happen to find one, i suggest to give it a try. At close range it's the best 180/200mm i tried on the full frame.
Unfortunately i like low light photography, so my new Tamron 180mm will likely have more chances to illuminate the sensor of my K-1.
I don't expect the Tamron to outperform the Sigma Macro at mid diaphragms, though.
Anybody else owns this Sigma?
cheers
Paolo