Pls help Summarit-M 75/2.4 not rounded bokeh circles WO?

[aCIDfire]

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Hello guys, I need some help identifying where is the problem with Summarit-M 75/2.4 - I bought it used for a good price in local store overall in perfect condition. Problem is with aperture blades wide open - when you look from the front of the lens, aperture blades are not fully retracted in barrel. In the barrel behind the aperture blades is a circle/rounded part so if you look through the lens from the back or front you see perfect circle. When I take some shots with OOF lights, bokeh circles wide open are not perfectly rounded,it looks like stopped down a bit. I tried it on my A7r II with 2 adapters (Voigt VM-E and TechartPro) - same result. Maybe there is some mechanical/electronic information for the lens when you put it on M body? I don´t have any leica M camera to try it. Where can be the problem? Any idea? Other much cheaper lenses have perfectly circled/rounded bokeh circles. 

My friend has 75/2.5 and told me that his lens is OK on A7 body. 

 

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[Echo63]

I have seen this behaviour in a lens before (can't remember which one though)

 

if you look at the centre, they are round, and towards the edges, it is flattened with the narrowest widest axis being 90 degrees from the centre.

 

 

I think it may have something to do with the lens appearing slightly oval when viewed from the side (where the light is coming from) and only looking circular when viewed straight on

[Hannes Lummes]

 

 

if you look at the centre, they are round, and towards the edges, it is flattened with the narrowest widest axis being 90 degrees from the centre.

 

No they are not round anywhere, not even in the center. Some of the aperture blades don't seem to open fully.

[david strachan]

It's as Echo says.  Edge light is vignetted, and caused oval shapes because your just not shooting straight down the light.

All lenses do this.

 

cheers..

[TomB_tx]

The OP notes that even in the "round" highlights you can see the aperture blade segments slightly forming a polygon outline on the blur circle, and this is his complaint, not the common football shapes on off center highlights.

This is a valid observation, but is very common on many lenses, especially where the aperture of the elements is slightly larger than the stated aperture, so the diaphragm is calibrated to trim the max aperture a bit to properly calibrate the f-stop. Many Leica lenses show the edges of the aperture blades when "fully open" for this reason.

I certainly don't consider it a defect, just a sign that the design makes sure the actual max aperture is not over stated.

[Michael Geschlecht]

Hello Everybody,

 

This change in image shape as the image gets closer to the edge of the format is called "mechanical vignetting".

 

It occurs because the image circle that exists for the light rays coming straight down the "tube" of the lens parallel to the axis is circular.

 

As the image comes from a greater & greater angle away from that axis: The partially cut off image image (which now is in effect going thru a "tilted tube") changes shape to what you are lookijng at as the image comes thru this "tilted tube".

 

Best Regards,

 

Michael

[DezFoto]

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Perfectly normal behaviour, nothing to worry about.

[aCIDfire]

Thank you guys! The lens is overall a great performer for portraits, landscapes. I send a message to a store where I bought the lens, they don´t have another 75/2.4 to compare but summarit-M 75/2.5 has the same slightly closed aperture blades wo. 

[lct]

Perfectly normal behaviour, nothing to worry about.

 

+1

[Hannes Lummes]

I don't have a single lens which wouldn't show perfect blur circles wide open in the center. My Elmarit M 90 was like that when I bought it (used), because the aperture blades didn't open fully, but Leica fixed it. Got to wonder how people find this is acceptable. Is it really that common? I have 10 lenses, all perfect.