50 Apo swirling bokeh

[Csacwp]

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My copy of the 50 Apo is blisteringly sharp but has swirling bokeh, especially when the background is busy with plants. Sometimes though it will even swirl smoother backgrounds, like if I took a 3/4 portait at a dirt road. Is this normal for the Apo? I’d say the amount of swirling is about half as much as my 75 Summilux.

[otto.f]

I don’t think anyone can say that without examples

[mmradman]

The way I read the post - background in my picture is busy and bokeh I am getting is also busy, my expensive APO Summicron is POS. What do you expect, mind reading lens able to alter busy into not so busy in keeping with the price tag?

 

I don’t see busy, M246 with APO 50mm.

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Edited January 18, 2018 by mmradman

[Csacwp]

My 50 apo would have swirled that... the bottom of the out of focus area would have curled upwards on both sides towards the top. I suppose this isn’t normal... I’m out of town now and restricted to a phone, but I can post examples of mine when I get home in a couple of weeks.

Edited January 18, 2018 by Csacwp

[mmradman]

Some say picture is worth thousand words. Please post examples of busy/swirly OOF. Is your lens first or later batch? Maybe send some sample images to mothership and request explanation.

[lct]

Please post examples of busy/swirly OOF [...]

 

+1

[Csacwp]

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Will do, I’ll post them as soon as I get home. It’s a current batch... I used to have one from the initial batch (no swirl), but Leica replaced it.

[adan]

Which type of swirly bokeh are we talking about?

 

There is this type: http://lensamanual.net/images/?id=2992 - due to optical vignetting

 

- or there is the type that comes from molded ASPH surfaces ("target" swirls within each blur circle):  https://www.reddotforum.com/wp-content/uploads/2014/10/Noctilux-50mm-f0.95-Bokeh-1200x520.jpg

 

I can see a 50mm f/2 lens in an E39 barrel - OR one with ASPH elements (or both, in the case of the 50 APO-Summicron) - producing either or both of those, under the right (or wrong) conditions....

 

...and consider it normal.

[Csacwp]

It’s sort of like the first image you linked to but not as severe. Reminds me a lot of the swirl from the 80 lux R. I thought the 50 apo was under no circumstances supposed to do that?

[LocalHero1953]

We need pictures

[Csacwp]

I will try to post some today... have to find an internet cafe.

[adan]

I can't imagine the APO-Summicron-M not doing that - in at least some situations. Optical vignetting (OV) effect.

 

Any lens that 1) has a large aperture value (f/2.0+) and 2) is not infinitely thin front to back, will get vignetting due to the fact that it is a long "tunnel" - the lens barrel itself crops the round aperture to a cat's-eye shape.

 

https://cdn.photographylife.com/wp-content/uploads/2013/10/Optical-Vignetting.png
 

....when used wide-open. And the APO-Summicron, like most fast Leica M lenses, does this also (note cat's-eye aperture when seen off-center).

 

http://www.meteor.com.hk/shop/11623-thickbox_default/apo-summicron-m-50mmf2-asph.jpg

 

Stopped down, of course, the aperture becomes small enough to avoid being cut off by the barrel, so we get a symmetrical, uncropped aperture, and even bokeh across the whole image. At, say, f/5.6 or smaller - which is likely about the aperture mmradman used for his picture above. (Note - BTW - that optical vignetting is vignetting - it makes the picture edges and corners darker because the aperture is effectively smaller and passing less light when cut off by the lens barrel).

 

http://doi.ieeecomputersociety.org/cms/Computer.org/dl/trans/tp/2010/12/figures/ttp20101222763.gif

 

Now, blur circles (i.e. the blurs that make the bokeh) take on the shape of the aperture as it appears from the image plane. So if a lens has OV, the blur circles around the edge take on the same cat's-eye shape as the aperture seen from that angle. And because the lens produces a circular radially-symmetrical image, the cat's-eye blurs also line up tangentially around the center of the image (i.e. at the top and bottom they are horizontal, and on the sides they are vertical, and in the corners they change angles in a curve from vertical to horizontal).

 

https://img00.deviantart.net/a43b/i/2016/010/3/8/swirly_bokeh_by_hispanhun-d9nffs0.jpg
 

....which is the primary cause of "swirling bokeh." All those "lined-up-in-a-circle" blurs can end up looking like circular motion blur.

 

However, it won't show up in every situation - it requires subject matter that in structure and brightness/contrast, produces strongly differentiated blur circles. Pinpoint lights, a dense pattern of leaves or branches silhouetted against bright sky, etc.

 

It is not a lens "aberration" (the glass misdirecting light, as with CA, or coma or astigmatism). It is just a physical cropping of the aperture. Therefore whether a lens is APO or ASPH or not is mostly irrelevant. It is just a function of squeezing a 50mm f/2 lens into an E39-diameter lens barrel.

 

I'd be interested in seeing some examples from your earlier 50 APO, which you say did not do this (at some point - no rush!). I suspect it was the situation (smaller aperture, softer-toned backgrounds) that avoided the effect being noticable, not an actual difference in the lenses.

[mdemeyer]

Jim Kasson in his blog “The Last Word” has written and published excellent material on this subject. It should be required reading for all with an interest (positive or negative) on bokeh.

 

I can’t find the start of the series on this, but here’s a post showing this for the APO-Lanthar 60 Macro lens.

 

http://blog.kasson.com/the-last-word/652-apo-lanthar-oof-psfs/

[mdemeyer]

http://blog.kasson.com/the-last-word/building-a-bokeh-simulator/

 

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