I've just acquired a mint secondhand 90mm Elmarit-M and would welcome some comments on the shape of the iris.

At all settings apart from two, the iris is a regular nine-sided shape, each side being a straight line (or almost so).

However, at 2.8 and the half stop between 2.8 and 4, the leaves don't come together in this way - there is a pronounced 'wave' effect from one leaf to the other.

Does this make any difference to the resulting picture? There seems to be some suggestion that the shape of the iris affects the out of focus details - does it make any difference to this?

My 50mm 'lux is regular at all stops; my 35mm 'cron ASPH shows a similar structure to the 90, but not as pronounced (perhaps because it's all on a smaller scale).

-- Paul Hart (paulhart@blueyonder.co.uk), May 17, 2002

Answers

Greetings Paul- I own this lens, too, and I have made the same observations of it's diaphragm shape- just the other day I was looking at this. But I have been shooting with this lens for more than a year, and never had any complaints with the results- actually I find the bokeh to be more than satisfactory. I used to own an older 90TE- the old Leica lens I have ever sold- and I don't miss it. I like the performance of this newer 90 Elmarit-M over all.

-- drew (swordfisher@hotmail.com), May 17, 2002.

Not to run these photos into the ground, but here is a representation of the 90mm Elmarit M's rendition of out of focus highlights compared to the Nikon 105mm f/2.5. Both images were made at f/4.0 and it is clear that the Leica shot has very clean OOF highlights... basically round compared to the 6 bladed Nikkor.

Use your lens at any aperture and enjoy it. It is one of the best medium telephotos out there.

90mm Elmarit M aperture shape and out of focus rendering of highlights

-- Al Smith (smith58@msn.com), May 17, 2002.

Paul: Aperture shape has some influence on the OOF areas - but so do the number of leaves, the position of the diaphragm in the optical path, the residual aberrations in the design, etc.

My 90 TE (thin) has a distinct 'gear' or 'star' shaped opening at the middle apertures (f/4.5 - f/11) and I notice the backgrounds are slightly more choppy than with the 90 'cron - emphasize slightly. However the TE is also modestly sharper, so I can't tell for sure if the difference is due to the aperture shape or simply the fact that the optics are just - different.

Shoot some pictures and report back - can YOU see 'waves' in the images?

-- Andy Piper (apidens@denver.infi.net), May 17, 2002.

Thanks to you all so far, and particulaly to Al Smith - the photos are helpful and the overall effect of the Leica lens is very pleasing...

I sold an 90mm APO ASPH to replace it with the more compact, manageable Elmarit-M and so far have no regrets...

Paul

-- Paul Hart (paulhart@blueyonder.co.uk), May 17, 2002.

I used to have a 35mm f/2.8 Summaron with diaphragm leaves that formed a complex aperture shape that changed from one f-stop to the next. I remember convex bumps intruding into the aperture. I didn't know bokeh from schmokeh back then, but I never saw anything to complain about.

-- Bob Fleischman (RFXMAIL@prodigy.net), May 17, 2002.