On 7/12/2011 10:20 AM, Carlos J. Santisteban wrote:
> Fernando wrote:
>> The bokeh seems odd to me: donuts appear in the OOF background as if it was
>> a catadioptric tele. - Of course, no one at the Flickr group noticed . . .
>> Do you find this somehow odd (or is it just me?) - if so, how can this be
>> explained?
> <http://www.flickr.com/photos/jikatu/5918710077/in/contacts/lightbox/><http://www.flickr.com/photos/jikatu/5918710077/in/contacts/lightbox/>
>
>
> I think it's an unhappy combination of things... first, it's not unusual for
> a Macro lens to be somewhat 'overcorrected' on spherical aberration, leading
> to ring-like backgroung highlights.
It's not limited to macro lenses. It is common in double-Gauss (Planar) designs
in the 'normal' to moderate tele focal
length range, as well as in many other highly corrected modern lens designs,
including many zooms.
The example you show is classic, highly corrected macro lens focused relatively
close, quite distant background with
point highlights. Many lenses will do that. For example look at this shot with
the Zuiko 50/1.8, miJ version.
<http://www.moosemystic.net/Gallery/tech/Lenses/Misc/5018bokeh.htm>
It's a useful example because it shows different stages of the effect. In the
upper left, it shows moderate problems,
with the edges bright, but the centers still partially bright, as well. At the
upper right, the bokeh has become bright
circles with dark centers. How much of the difference is due to different focal
distances and how much to the different
sizes of the the highlights, I can't be sure. The Zuiko 50/3.5 macro can be
even worse.
There are explanations with examples here
<http://www.kenrockwell.com/tech/bokeh.htm>
and here. <http://www.luminous-landscape.com/essays/bokeh.shtml>
Although they have different causes, this kind of bokeh and mirror lens OOF
rings can look quite similar. This mirror
lens image could easily be mistaken for non-mirror lens bad bokeh.
<http://www.moosemystic.net/Gallery/tech/Lenses/Sigma600/Juniper.htm>
Notice that I didn't mask the sharpening, and just what Carlos mentioned
happened, sharper rings.
In other cases, mirror OOF rings are clearly not bad ordinary bokeh.
<http://www.moosemystic.net/Gallery/MPhotos/Maine/Sigma600/pages/12_1695lces.htm>
> And if the picture has been over-sharpened a bit, those rings may look like
> in the picture you say.
>
> In other words, if you look closely, unlike those from mirror lenses, these
> donuts aren't "hollow", really ;-)
Exactly, but in some cases, that distinction just isn't obvious.
Ring Around the Moose
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