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Elmarit-M 90mm - aperture wide open non-circular?


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Hi all,

a while ago I've bought a used Elmarit-M 90mm (latest version) for which I found a few days ago by accident that the aperture blades do not fully disappear when the lens is used wide open. Consequently, the bokeh balls aren't circular, but have a more "saw blade"-like shape. If I turn the aperture ring beyond 2.8, which is possible by a tiny bit, the blades retract a bit more, but never completely (cp. attached images). 

As I wasn't sure whether this is by design or a defect, I have contacted Leica Support and they tell me that this is the normal behaviour, but offer a CLA for the lens nonetheless.

Could any other owner please check with his or her lens?

Thanks in advance,
Rolf

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I think this is due to inaction over time. Most mechanisms benefit from periodic exercise, especially when lacking regular usage. 

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21 minutes ago, wda said:

I think this is due to inaction over time. Most mechanisms benefit from periodic exercise, especially when lacking regular usage. 

Actually, no.

This is often normal.

Leica has an old-school idea about lens construction: design the lens (glass) with margin for error, and then install and adjust the moving aperture to the calibrated required aperture diameter needed for the exact focal length of the individual unit.

This sometimes results in the calibrated aperture opening being smaller than the round glass elements.

For example, with the 90 Elmarit, Leica assembles the lens, and then measures its precise focal length, which may be 89.5mm, 90.0mm, 90.5mm or 91.0mm.

Since the maximum focal length can be as high as 91 mm, the glass is designed to be 91mm/2.8 or 32.5mm across (at the exit pupil).

A lens that that is measured as an 89.5mm lens needs an opening of 89.5/2.8 = 31.96mm > 1.04 mm smaller than the maximum. The aperture leaves are thus adjusted to that smaller diameter, and the leaves begin to show around the edges.

Additionally, Leica also adjusts the brass focus cam at the back,  that connects to the camera, based on the final measured focal length - an 89.5mm lens will focus slightly differently than a 90mm lens.

Look on the Elmarit's focusing ring right beside the infinity mark and you will find two tiny sideways numbers that indicate the exact focal length of that particular lens example.

For example,    05    engraved on the lens indicates the true focal length of that actual unit is 90.5mm.

Those numbers are there so that if the lens is ever sent in for service, the techs will know exactly how to adjust it specifically.

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1 hour ago, adan said:

Actually, no.

This is often normal.

Leica has an old-school idea about lens construction: design the lens (glass) with margin for error, and then install and adjust the moving aperture to the calibrated required aperture diameter needed for the exact focal length of the individual unit.

This sometimes results in the calibrated aperture opening being smaller than the round glass elements.

For example, with the 90 Elmarit, Leica assembles the lens, and then measures its precise focal length, which may be 89.5mm, 90.0mm, 90.5mm or 91.0mm.

Since the maximum focal length can be as high as 91 mm, the glass is designed to be 91mm/2.8 or 32.5mm across (at the exit pupil).

A lens that that is measured as an 89.5mm lens needs an opening of 89.5/2.8 = 31.96mm > 1.04 mm smaller than the maximum. The aperture leaves are thus adjusted to that smaller diameter, and the leaves begin to show around the edges.

Additionally, Leica also adjusts the brass focus cam at the back,  that connects to the camera, based on the final measured focal length - an 89.5mm lens will focus slightly differently than a 90mm lens.

Look on the Elmarit's focusing ring right beside the infinity mark and you will find two tiny sideways numbers that indicate the exact focal length of that particular lens example.

For example,    05    engraved on the lens indicates the true focal length of that actual unit is 90.5mm.

Those numbers are there so that if the lens is ever sent in for service, the techs will know exactly how to adjust it specifically.

Andy, thank you for that information. I hadn't realized that Leica continued the practice of marking lenses produced as late as the last 90 mm Elmarits. Mine, one of the last to be coded, actually shows '10' in very tiny figures, though it is of academic interest to me.

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Thanks guys for your feedback and the interesting discussion so far - I had never noticed the tiny figures on the focussing ring.

Coincidentally, mine also shows a "10" for this particular lens. Therefore, David, I would be interested whether for your lens the aperture blades do in fact fully retract.   

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50 minutes ago, robotography said:

Thanks guys for your feedback and the interesting discussion so far - I had never noticed the tiny figures on the focussing ring.

Coincidentally, mine also shows a "10" for this particular lens. Therefore, David, I would be interested whether for your lens the aperture blades do in fact fully retract.   

My iris blades closely resemble yours at full aperture.

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My lens also has the small number 10 but looks almost circular. However, I just had the lens returned from Leica USA (great service by the way), where it was given a CLA and 6-bit coding. Regrettably I do not remember how it looked before servicing.

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My 90mm Elmarit, also a 10, is not perfectly round at f2.8 (barely shows sawtooth effect) but appears round to me as I move the aperture ring more open than f2.8. Hasn’t bothered me but i will look for this effect.

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Posted (edited)

I have a 90mm Elmarit-M "10" (in other words a 91mm lens) and when the aperture is set to f/2.8, the bokeh balls have a slight saw-tooth shape. However, I can turn the aperture ring slightly beyond f/2.8 and this opens the aperture blades fully and then the bokeh balls are circular.

Edited by LarsHP
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Posted (edited)

For visual reference, here's two bokeh ball shots with my 90mm Elmarit-M respectively at f/2.8 setting and slightly beyond the f/2.8 mark.

This makes enough difference that when shooting subjects where bokeh quality is important, I turn the aperture past the f/2.8 mark, but for images where this isn't the case, I just set the lens to f/2.8. I don't see any exposure difference.

The images are crops from the center of the image and in 100%.

Edited by LarsHP
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Posted (edited)

Similar here - although I no longer have the elmarit (and yes regret selling it - chrome 6bit) -  I remember I used to hold the aperture ring beyond 2.8 when there were bright highlights in the background...

 

Edited by NigelG
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Ok, my interest was peaked. My results from a quick test show a more circular OUF ball at f/2.8. Certainly not perfect, but nothing I would be disappointed about. The nudge past f/2.8 looks better though.

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4 hours ago, cbarber said:

Ok, my interest was peaked. My results from a quick test show a more circular OUF ball at f/2.8. Certainly not perfect, but nothing I would be disappointed about. The nudge past f/2.8 looks better though.

 

What precise focal length does your lens have? (Check the small two-figure number next to the "m" on the distance scale.)

Your lens seems to have less saw-tooth and difference between fully open and clicked at f/2.8 than my sample.

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19 hours ago, LarsHP said:

What precise focal length does your lens have? (Check the small two-figure number next to the "m" on the distance scale.)

Your lens seems to have less saw-tooth and difference between fully open and clicked at f/2.8 than my sample.

The small number is ’10’.

Attached is a photo taken at f/2.8. My lens does not seem to exhibit the degree of jaggedness that the lens in OP images show at f/2.8. I’ve had the lens for many years and recently decided to have Leica service it. Perhaps that has helped.

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2 hours ago, cbarber said:

The small number is ’10’.

Attached is a photo taken at f/2.8. My lens does not seem to exhibit the degree of jaggedness that the lens in OP images show at f/2.8. I’ve had the lens for many years and recently decided to have Leica service it. Perhaps that has helped.

 

Okay, then my sample has slightly more aperture "cut" than yours even though it's the same exact focal length. I don't consider it an issue as long as I can just open the aperture beyond the f/2.8 mark.

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