Hi Jan,
I have used the Olympus 50 mm macro on the E-410, E-510, E-520, E-3 and I am now testing the new E-620/PT-E06 combo and these are my thoughts.
When the Sigma 105 macro first came out I was put off by the fact that you could not shift from Af to manual while the lens is in a housing. Then I continued to hear the reports of poor AF speeds which are amplified by low light conditions found in many U/W settings. Athena makes the best port for this lens and I am not sure if it will fit into your Inon port.
Olympus has had the 100 mm macro on the "road map" for over four years now, before the Sigma was released. It is now the "ONLY" lens left on the 2009 road map which has not been released so perhaps it may at last come by years end.
I have used the following combos with excellent results, 50 & 35 plus the 1.4 tele converter using the Athena posts for these lenses and the Athena 1.4 extension ring.
I also use the Inon M-165 diopter. The same combos can be used with the 50 macro and your Inon port. I like the Inon port because you only need one gear for manual focus with any of the lens combos.
I also use the 50 & 35 macros with the 2 X tele converter and the Athena extension ring. The 35 has a hard time in AF because it becomes about an F/7 lens. The 50 however will AF quite well in average light. With the M-165 you have about a 1.6/1 or 3.2/1 in 35 mm terms ratio. This allows for some very small critters and requires a bit of practice. I did a three hour dive at the Blue Herion Bridge yesterday with the 50/ 2 x tele combo plus diopter combo and was able to get off over 240 images.
My understanding is that the fine ReefNet Co. +10 diopter is being released in a 67 mm thread which would take the 50 mm from 1:2 to 1:1 or twice life size in 35 mm terms. The ReefNet lens will be the most cost effective way to get the 50 to 1:1 but will reduce the working distance. The 1.4 & 2 X tele converters add working distance.
The combo I use most is the 50 macro & 1.4 tele with the M-165.
Photo #1-50 mm macro with 2 X tele converter at 1:2 (lens fully extended)
Photo #2-50 mm macro with 2 X tele converter at 1:2 (lens fully extended) Inon M-165 C/U lens.
Photo #3-35 mm macro, crab in glass tube.
Phil Rudin
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