Re: [OM] IMG: Wednesday Observations

Subject: Re: [OM] IMG: Wednesday Observations
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Thu, 21 May 2020 11:30:13 -0800
Acrobatic Eyes Moose wrote:
> Unfortunately, the bokeh makes my eyes spin in my head. A common problem with 
> 50 mm lenses and certain combinations of
> subject and back ground distances. I've got even uglier examples from the OMZ 
> 50/3.5 macro and 50/1.8.

On this specific picture, I definitely agree. There is a combination
of camera-subject-background distances, texture, aperture, and image
processing which can create a rather "busy" background. Most 50mm
lenses tend to be subject to this a little more than the average bear.
My 35/2.8 and 100/2.8 are also lenses which will go nuclear on you in
some combinations, but are otherwise pretty glorious.

What surprises me is that the Four-Thirds 50/2 Macro was specifically
engineered to avoid this trait as much as possible. I think this is
more of a one-off situation, where the optical "frequency" of the
background created an interference pattern with the lens
characteristics. As the lens is highly corrected for the focus plane,
the out-of-focus blobs will reach a maximum spread and then can fold
back in on themselves generating ring patterns. This 50/2 is generally
very resistant to the fold-back ring issue.

The newer lens designs can be very different. Today's primes are more
like fixed focal length zoom lenses. The image is generated by a
couple of lens groups and then magnified/reduced by another group.
Focus adjustment is internal--again, just manipulating the focus point
of the image already generated. The primary lens groups are so
optimized for a focus trait or bokeh, and the other lens groups
essentially apply a diopter to correct the actual focus.

I was curious how the Sony SEL2870 handled close-up stuff (reasonably
close up as it isn't macro). This lens very much follows the above
model as it has a hard limit on the bokeh blob spread and is applying
internal focus correction and zoom to "tweak" the response. It's a
very "dry" lens that imparts no "character" on the image. It's
respectable, but the images have a clinical look that makes me want to
mimic our toy poodle when she has some fuzz in her mouth and does that
backwards licking thing to get it out. It's to lenses, what a Taco
Bell $1.29 hardshell is to Mexican Food. Usually edible, but...

AG Schnozz
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