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10-26-2008, 07:27 PM   #16
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@ Nesster - it seems quite surprising to get that much bokeh (and with that funky SA) from a 35/2.8 and not so close to the minimum range by the looks of it?

I've found a copy in poor condition and am awaiting some questions answered before delving in - I may hold out for a cleaner copy.

Thanks for the cool examples.

QuoteOriginally posted by k100d Quote
Zeiss has a few 135mm, 180mm , and the Jupiter-9 is a Zeiss clone
True - I was thinking specifically of the 50/1.5 based on your linkage above. Anything pertaining to SA at this point. It'll be my new bokeh obsession until I settle on the right lens for the job. I wonder if the other Sonnars were also under-corrected? I'll have something else to investigate now, lol.

QuoteOriginally posted by sharko Quote
Is spherical aberration basically the "swirl bokeh" that some older lenses tend to have?
Well, I believe to a certain degree, yes. There are many forces at work here that I don't yet fully understand, but uncorrected spherical aberration can give the background a concave appearance among other things and can also add a gentle glow to oof edges (see Nessters samples above). It seems over the years some lenses, such as the aforementioned Sonnar 50/1.5, specifically under-corrected for SA to gain this effect. In other cases, it was probably due to inferior optical formulation - but it still comes down to taste.

I'll try to find a link I'd read some time ago that attributed swirlyness to something else, or hopefully someone currently in the know will chime in.

10-27-2008, 06:23 AM   #17
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Here are some bokeh "rings" from my Sigma 30mm f/1.4 -

10-27-2008, 09:26 AM   #18
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I'll try to describe what it is (and why I'd want it in a photograph) visually -

Why SA's occur -

"Spherically shaped lenses and mirrors share a problem: their shape. Parallel light rays that pass through the central region of a spherical lens focus farther away than light rays that pass through the edges of the lens. The result is many focal points, which produce a blurry image"



Here, SAs effect on field curvature -



Its effect on sharpness -



Examples in photography - only one of these are my pictures, the rest are probably copyrighted to their original owners (attributed as described) -


by Brian Sweeney


2 by Samuli Ikäheimo




by futureancient




by Balrog


one by me - the Zeiss T*25 at minimum focus distance is uncorrected for such close distance (its fine outside of 6 inches, but as you close past that, note the bottom right in a motion like swirl)


And there you have it.
10-27-2008, 10:20 AM   #19
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personally 2, 4 and 6 have really distracting bokeh to me but i do love the swirly bokeh effect.
the noctilux is also a famous lens that has such a property.

10-27-2008, 11:04 AM   #20
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QuoteOriginally posted by thePiRaTE!! Quote
@ Nesster - it seems quite surprising to get that much bokeh (and with that funky SA) from a 35/2.8 and not so close to the minimum range by the looks of it?
Actually the behavior seems most pronounced at middle distances.


Here's another thread from a while back that goes over some of the same ground

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/17970-bokeh-sp...ng-result.html
10-27-2008, 11:08 AM   #21
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QuoteOriginally posted by k100d Quote
personally 2, 4 and 6 have really distracting bokeh to me but i do love the swirly bokeh effect.
the noctilux is also a famous lens that has such a property.
Ah yes, the Noctilux. I've said it before: if someone would take my money for an f1 in K, I'd gladly part with it. That said, the older Noc has a 3m minimum focus distance... thats quite a lot! The newer one is better (I think I read 1.1m) but is astronomically priced. Even I'm not that crazy, lol.

As for the samples - yeahp, ymmv (though fwiw, I love them all). I'm hoping they might trigger some more lens suggestions. I'd like to try a few different SA offenders (on the K20) and decide which one tickles my fancy before likely moving on to some other arcane bokeh tidbit to fascinate over, hehe.

Regards,


Kelly.
10-27-2008, 11:11 AM   #22
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QuoteOriginally posted by Nesster Quote
Actually the behavior seems most pronounced at middle distances.


Here's another thread from a while back that goes over some of the same ground

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/17970-bokeh-sp...ng-result.html
Sweet. Thanks again Nesster - I'll read it through shortly...
10-27-2008, 11:33 AM   #23
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QuoteOriginally posted by k100d Quote
personally 2, 4 and 6 have really distracting bokeh to me but i do love the swirly bokeh effect.
the noctilux is also a famous lens that has such a property.
4 and 6 look like the blur disks in the background are vignetted (+ a spherical aberration effect). The blur disks aren't symmetric; only the edge facing the center of the image is sharp.

On 2 you can see sharp edges surrounding the entire blur disk -- which makes me think that the blur disk is not being vignetted but merely distorted near the borders of the image.

10-27-2008, 01:04 PM   #24
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you might like this, not SA specific, but from RangeFinder people who are very conisseurish
The ultimate Bokeh thread; pics please - Rangefinderforum.com
10-27-2008, 07:48 PM   #25
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Lots of files of my work get dumped due to unpleasant bokeh.
So, I started to look for alternatives.

I attach three files. The first is a Zeiss M 50/1.5 that Kelly referred to above. The second two used a "soft focus" lens which which allows one
to shift an aspherical element. So maybe this post is not too far off topic.

In a landscape pic, I find leaves hard to photograph and I am pleased
with the softness and mystery.

gary
Attached Images
     
10-27-2008, 08:36 PM   #26
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QuoteOriginally posted by gtmerideth Quote
Lots of files of my work get dumped due to unpleasant bokeh.
So, I started to look for alternatives.

I attach three files. The first is a Zeiss M 50/1.5 that Kelly referred to above. The second two used a "soft focus" lens which which allows one
to shift an aspherical element. So maybe this post is not too far off topic.

In a landscape pic, I find leaves hard to photograph and I am pleased
with the softness and mystery.

gary
I like that red leaf photo Gary, very smooth. You have such a strong collection of lenses, I envy you!

Are these crops? I'd like to see the whole Sonnar shot. You can start to see a bit in the top left of highlights, but I can't tell if its 'swirly'. Do you find it shows a lot of SA wide open? I noted after reading up that the old version of the lens had three elements to the 5 of the newer one, makes me wonder if Zeiss didn't rectify to some extent the amount of SA?
10-28-2008, 10:31 AM   #27
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The Sonnar shot is the full frame minus a little crop off the right hand side.
The shot is very representative of what the lens accomplishes wo. Everything is soft, progressively, fore, mid and background. The design of this lens found a niche in shooting head shots of Hollywood stars in the 30's and 40's. Soft glowing edges.

I don't know how to answer your question about SA. The soft focus lens uses element movement technique but produces a completely different result. I did a lot of Polaroid transfers, when that was going on, and the soft focus prints are very close. The prints look nothing like those on the screen.

Back to the topic. It is known that the Sonnar design has tendancy for
SA but is more successful than Planars for low flare and high contrast.
So, your exploration might take you to identifying Pentax compatible glass which uses the Sonnar design. Six or seven elements in three groups.

It's a fascinating subject and thanks for getting our minds going.
g.

Last edited by gtmerideth; 10-28-2008 at 10:39 AM.
10-28-2008, 05:18 PM   #28
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QuoteOriginally posted by gtmerideth Quote
...It is known that the Sonnar design has tendancy for
SA but is more successful than Planars for low flare and high contrast.
So, your exploration might take you to identifying Pentax compatible glass which uses the Sonnar design. Six or seven elements in three groups.

It's a fascinating subject and thanks for getting our minds going.
g.
So far I've determined 1957 Takumar preset 55/1.8 & 2.0 were based on the Sonnar. There was another 55/1.8 in the same year that was a different optic formula as well, so it could get a bit confusing (comparing serial numbers, etc) These might pose a challenge to locate.

Also, Leitax (a company producing adapters to use Leica R-mounts on Pentax K-mounts.) Has produced an adapter to use Zeiss Contax lenses on K as well. In that line-up are an 85 and 135mm in Sonnar.

Personally though, I think I'd be more interested in the older 50mm range stuff - probably the Takumar as it would likely be more apt to produce obvious SA.

I've also noticed that the Takumar 135/3.5 (the older the better) was an SA offender, thanks Jay for reminding of the Taks.

My first research subject should be here in a few days, I hope to have some pics up soon.

K.
10-28-2008, 08:17 PM   #29
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i am eagerly awaiting you're final decision!

there was a thread a while back about the zeiss biotar 75/1.5 i think in which we started talking about "swirly" bokeh (a little too vague a term i think).

spherical aberration mostly causes blurriness i thought? i was under the impression (thanks to the biotar thread) that the "swirling" oof highlight effect was caused by optical vignetting (the so-called cat's-eye effect). someone in that biotar thread also pointed out that the "swirliness" is also caused by astigmatism.

many of the photos in this thread show the cats-eye effect, which is something i am lusting after a bit myself (i think it would be more difficult to achieve with 35mm lenses on an aps-c format though since the image circle is being cropped).

am i wrong? or maybe you are really looking for an astigmatic, optically vignetting lens?

i found the biotar thread (kelly, you should be aware of it, it looks like you posted in it as well - responding to me infact!): https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/27552-zeiss-je...iotar-m42.html that is another lens that i would love to have, if only it didn't go for soooo much on ebay.
10-28-2008, 10:16 PM   #30
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You might be entirely right. I may be misappropriating what I'm seeing to the wrong phenomenon.

I guess the lenses I've undertaken to source for this will likely thus end up a mixed bag of performers... I might still find what I'm looking for, if a little blindly it seems.

...and absolutely YES - aps-c is cropping and straining all my wonderful FF glass! I keep hoping for a FF body, but having said that, in-body shake reduction and value brought me to this platform and I still really appreciate both aspects above all else. I definately feel a nearly overwhelming sense of wanting to get into an M8, but $$$... I just make the best with what I've got myself into (also fairly blindly) and I'm pretty happy in that thus far.

Thanks for posting that link, it totally slipped my mind. It would have saved a lot of re-sourcing of info in google. My mind is like a sponge... a small one. I soak up everything and replace it. Honestly though, I only sleep a few hours a night while I get on a bender to learn something, it's all be very interesting - really appreciate the advice and linkage from everyone.
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