[JinDesu]

Bokeh shouldn't just be evaluated by itself. It's part of an image. Did you want the in focus subject to stand out? Did you want it to melt with the background? Did you want the blurred background to stand out? Did you want to incorporate lines in the background with the subject? Etc. All those factors are important to how pleasant bokeh is, in addition to how the blurred specular highlights are formed by your lens.

[Canada_Rockies]

causey, somehow my lightroom did not show EXIF (need to figure out settings). The "nervous" bokeh pic is 1/320, f 5.6, ISO 250. I see what you mean. Need to shoot more pictures.

When exporting to JPEG, make sure you select ALL METADATA when you export. It's about 2/3 of the way down the export dialog.

[micromacro]

When exporting to JPEG, make sure you select ALL METADATA when you export.

I changed that to copyright only long time ago and forgot. Thanks!

[bdery]

and also most likely experience in photography.

What do you mean by that?

[micromacro]

What do you mean by that?

I mean my lack of experience in photography. You can see something I can not see yet because I don't understand where to look.

[bdery]

I mean my lack of experience in photography. You can see something I can not see yet because I don't understand where to look.

That may be so, and indeed the "initiated" sometimes sees qualities in a work of art (whatever the type) that others won'T see. that being said, if you don't like the look of a particular lens' rendering, it's perfectly all right

[Lowell Goudge]

I see a lot of discussion about good bokeh, bad bokeh etc... So let's look at things a little more pragmatically.

There are, from my experience a fixed number of things that influence bokeh, although simple. In concept and easy to discuss qualitatively , quantifying these concepts is very complex. In fact one forum member was doing a PHD on the subject a few years ago. So here goes the list.

- focal length. This has a big influence because a lot of times smooth creamy bokeh is the result of relatively high magnification of the background relative to the foreground. This is simply a function of the ratio of background and foreground distances divided by focal length. The shorter the focal length the smaller the background relative to foreground so things take on a harder stronger appearance then if the same subject is shot with a long focal length and the out of focus items are larger.
- iris position. Not sure how to best describe this, but my experience with many preset lenses is that for any given aperture when compared to modern lenses, the rendering of the out of focus region is completely different. Inattribute this to the fact with many presets the lens design has the aperture close to the front element.
- iris shape, generally the rounder the aperture. The better the bokeh. Lenses with only 5-6 blades that collapse to a pentagon or hexagon seem to produce hard bokeh. Additionally they produce star bursts around bright points. This can be used creatively also. You get one line per corner that bisects the entire frame, therefore you get the impression of double the number of "spokes" with an odd number of blades, or the same number of spokes with even blade counts. If the blades do not close equally you get pairs of parallel spokes. Also some presets have sculpted blades that make mid aperture settings look like a flower. These produce interesting, but somewhat "cluttered" bokeh
- optical artifacts, somebody mentioned mirror lenses. These produce donuts due to the same principle as vignetting, but they are donuts instead of rounded images because the obstructed light is in the middle of the frame
- uniformity of illumination. When you get out of focus points turning into circles, the uniformity of illumination across the circle can greatly influence the bokeh. When looking at how a lens behaves check for hard vs soft edges on points of lights blown into circles, and look for brighter spec enters as opposed to edges, this can give better creamier results
- longitudinal CA. Look for lenses that produce green halos due to longitudinal CA, especially in B&W shots this can be very pleasing

The moral of the story is consider the above, and go out and play. Great bokeh is technique, and understanding how a lens behaves.

[micromacro]

In fact one forum member was doing a PHD on the subject a few years ago.

PhD on bokeh.Wow!
Thank you for such a detailed technical explanation. However the evaluation "good-bad bokeh" will be a quite mystery for me. From an artistic point of view I mean.

[wayne james]

no expert, here these were shot in the afternoon sun with a pentax 77 @ f1.8

[Lowell Goudge]

no expert, here these were shot in the afternoon sun with a pentax 77 @ f1.8

No, perhaps no expert, but the shots do show some of what i was talking about.

If you look closely at the shots, you can see the impact of uniform illumination through out what would be the circle that a point would generate. You can see what appear to be well defined wide arcs and lines from What must have been blades of grass or plant leaves. Where the edge of the out of focus appears, it is still a relatively hard line. Although if tie illumination of the out of focus area was brighter at the edge, it could be much worse

---------- Post added 05-25-2014 at 01:13 AM ----------

PhD on bokeh.Wow!
Thank you for such a detailed technical explanation. However the evaluation "good-bad bokeh" will be a quite mystery for me. From an artistic point of view I mean.

But it does not need to be a mystery. That is the point. The guy doing the PHD was doing it in advanced optics and math. Ok fine, very complex to make a quantitative analysis, but if you break things down to individual components, and try each component, you can get a qualitative understanding

Maybe set some "guidelines"
-Long better than wide
-round aperture better than geometric
-background further away from subject
-bigger background subjects better than small. Bigger =blotchy , small=confusing

The other thing to consider is aprochromatic lenses are not always the best, lenses with some lateral and longitudinal CA (read this as older lenses) can produce much better bokeh due to the separation of color in the background. This leads to less defined edges.

This last point is why some old lenses are sought after. Remember , every lens has a purpose, and it is your job to play with your gear until you know what every lens can do in every situation.

[Kerrowdown]

evaluate test bokeh of that lens

For me it's quite simple, is the end result pleasing to the eye, no science or clever measuring of anything for me.

[micromacro]

no expert, here these were shot in the afternoon sun with a pentax 77 @ f1.8

I really like #2 bokeh for such a contrast between round flower and straight bokeh lines. Very interesting.
On #1 I see yellow spots on background. I get them pretty often too, especially on big crop. I managed to get rid of them in lightroom reducing yellow color saturation, but it does not work well all the time depending on other colors balance.

It would be useful to know what causes those spots and how to avoid them. Do you know?

---------- Post added 05-27-14 at 08:04 AM ----------

Remember , every lens has a purpose, and it is your job to play with your gear until you know what every lens can do in every situation.

I leaned that for sure because I'm still testing and testing lenses instead of knowing them

[wayne james]

For me it's quite simple, is the end result pleasing to the eye, no science or clever measuring of anything for me.

yep, that about some's it up for me too.
I just play with the f-stops and shoot. then I figure out what works best for me.

now Mr Lowell Goudge would you mind posting some of your pictures, so we could understand / learn a little more.
Thanks

[Lowell Goudge]

yep, that about some's it up for me too.
I just play with the f-stops and shoot. then I figure out what works best for me.

now Mr Lowell Goudge would you mind posting some of your pictures, so we could understand / learn a little more.
Thanks

Check the early threads in the 135mm lens club, I compared a preset 135mm lens heads up against a more conventional (in terms of aperture) 135/3.5 SMC tak.

Also check the preset lens club, for examples of what lenses with round, forward placed apertures can do.

Lastly, check here, and look at examples, then think about my comments to see if you can identify the different points

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/132843-bokeh-club.html

[micromacro]

I think this bokeh is pretty good. Am I right? It's Vivitar VMC 135 f/3.5


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