I FINALLY Understand... Bokeh & Aperture Roundness

[Old-N-Feeble]

It finally "clicked" in my diseased old brain.


I've often pondered the elusive "creaminess" of the out-of-focus areas of some lenses. What appeals strongly to me are sharp highly corrected high-contrast lenses with lots of aperture blades. None of my modern lenses have such an aperture. They all have the typical out-of-round apertures.


I DO realize there are other qualities that differentiate modern lenses from classic but... it's ONLY the round apertures that interest me.


Are there modern shutters into which I can transfer my #0, #1, and #3 sized cells? I realize I'll need new scales. That's okay.

BTW, I don't need flash sync.

 

[BrianShaw]

Mike, I think the days of lots of aperture blades ended in the 1950's or 1960's.

 

[BrianShaw]

You might be able to find some later Compur shutters and swap your modern cells into them.

 

[Old-N-Feeble]

Thanks... I'll search for Compur shutters.

 

[BrianShaw]

My experience, though, is that the lens bought in an older Compur shutter is just as good as a newer lenses.

 

[Maris]

Round apertures are available for all lenses merely by using lenscaps with nicely made holes in them.

With normal and long focal lengths the problem of vignetting tends not to arise but wide-angle lenses (particularly retrofocus designs) need testing individually. But why stop with round apertures. Try squares, triangles, stars, flowers and so on. Years ago I did a portrait shoot with a lens masked with black paper bearing the cut-out initials of the subject. The final picture repeated those initials in every out of focus specular highlight!

 

[Nicholas Lindan]

Bokeh has little to do with the shape of the aperture (within reasonable limits, of course).

A lens with unacceptable bokeh with a 5 or 7 blade aperture will have unacceptable bokeh with a perfectly round aperture.

Interestingly a lens that has terrible bokeh for things that are more distant than the focus point will have wonderful bokeh for things that are nearer.

 

[John Austin]

Bokeh* as I understand it is a function of the way spherical aberration is corrected, or not - The following chart is the best description of Bokeh I have yet found - It is from the 1897 book by Conrad Beck



However, a modern aperture will give a funny shaped circle, but as good bokeh is considered to be smooth with circles of out of focus light shown without a harsh edge that becomes less of a problem - When looking for lenses for LF the OOF zones are a deciding factor in my decision, one of the reasons I like my Heliars**

* "Bokeh" is too trendy a term and like everything else they name the Japanese did not discover or invent it, proof of which is the Beck illustration

** The failings of Heliars is subject for another discussion which I am sure has happened in the past - To me it is a problematic design which perfectly suits some subjects - I do not use my Heliars for landscape photography and prefer my better balanced Skopar, Xenar and Ysarex designs

Now to scan last week's images for email proofs to a client before the big silver jelly prints get made - After that I get the money which will all go to a dentist for some crowns - One of the joys of aging

John

 

[Old-N-Feeble]

I think, with the highly-corrected modern lenses I'll be using, that aperture roundness is the limiting factor. Would it help if I listed the lenses?

 

[John Austin]

No need for a list - Look through a backlit tree and see how the OOFs appear - Then visit as many other LF photographers and do the same with their lenses - After that make your lens set decisions - Many older designs had a better balance of corrections and this balance seems to have been lost in the thrust for sharpness at the loss of equally important properties

 

[polyglot]

"Highly corrected" does not imply good bokeh at all, it just means that spherical aberration is well corrected. As it happens (over-)correction of SA tends to cause terrible bokeh and some of the prettiest bokeh you'll see comes from lenses with severely under-corrected SA. The SA causes the edges of the highlight discs to be softly rounded off; exactly correcting for SA results in sharp-edged bokeh and over-correcting SA (a common approach to getting a bit more sharpness) results in nisen-bokeh, i.e. line doubling because the edges of the highlight discs are brighter than their centres.

If you want the ultimate in bokeh, you need to use an apodisation filter by the aperture, e.g. Minolta's 135 STF.

 

[Moopheus]

If you want the ultimate in bokeh, you need to use an apodisation filter by the aperture, e.g. Minolta's 135 STF.

So, "ultimate bokeh" means "almost completely featureless backgrounds"? It's kinda dull, actually.

 

[John Austin]

In the end I don't do the sums, just look at a lens' image before deciding if I like it - But I still think overall balance of properties is more important than just sharpness

I am surprised no one has attacked me for commenting on the properties of early Heliars

 

[Old-N-Feeble]

Grumpy... That's precisely what I'm doing. I'm making an overall observation that very round apertures make better images (stopped down a bit) than octagonal ones. Lately, that's become very obvious to me. Though, lately, my powers of observation and logic are weak.

 

[Leigh B]

And the reason you've splattered this same nonsense across (at least) three different fora is ______?

- Leigh

 

[polyglot]

If you shoot 35mm, have a look at some images from a CZJ Flektogon 35/2.4. Hexagonal (and very obviously so) aperture, but still beautiful bokeh; Dead Link Removed Dead Link Removed (digital photos of no artistic merit, but nevertheless an illustration of the lens).

 

[steven_e007]

I thought 'bokeh' was just a word you slipped into the title on eBay to try and get a better price for your lens.


.... like 'petzval'.

 

[John Austin]

"Highly corrected" does not imply good bokeh at all, it just means that spherical aberration is well corrected. As it happens (over-)correction of SA tends to cause terrible bokeh and some of the prettiest bokeh you'll see comes from lenses with severely under-corrected SA. The SA causes the edges of the highlight discs to be softly rounded off; exactly correcting for SA results in sharp-edged bokeh and over-correcting SA (a common approach to getting a bit more sharpness) results in nisen-bokeh, i.e. line doubling because the edges of the highlight discs are brighter than their centres.

If you want the ultimate in bokeh, you need to use an apodisation filter by the aperture, e.g. Minolta's 135 STF.

Hang on, what I actually typed was "I understand it is a function of the way spherical aberration is corrected, or not" - I have added the bold type

 

[johnielvis]

you want round,do what maris says with the lenscap OR you can cut your own disks and put them in place of where your aperture blades are--right in the shutter provided the lens doesn't cramp in there. Or get a process lens with waterhouse slides and use perfect circles..

easiest is what maris said--I use front aperture all the time with projection lenses--works great--the old polaroid cameras used this for like f90 or something--thelenscap had a hole in it for that purpose.

 

[Old-N-Feeble]

Okay... if "some" spherical aberration is necessary to produce nice bokeh then maybe I should be looking for Imagons, SF Ektars, SF Fujinons, etc. I'd only use the discs with the periferal holes closed though. I hate the effect created with them open. I'd definitely use them "stopped down" a bit. Am I crazy or is this one way to get what I want?

 

[Old-N-Feeble]

RE: front aperture. Doesn't that degrade image quality in other ways? I thought the aperture needed to be placed precisely at the nodal point. Also, that method wouldn't work with lenses of shorter-than-normal focal length would it? Maybe I'll give it a try.

 

[Old-N-Feeble]

And the reason you've splattered this same nonsense across (at least) three different fora is ______?

Why do you care, Leigh?

 

[BrianShaw]

... actually, Mike, I had similar thoughts. I find it difficult to remember which forum I responded to, and don't like having to re-read entire threads to figure out what's been said here or there. But I'm not criticizing. I'm getting old and feeble-minded too it seems.

 

[Old-N-Feeble]

Understood... I realize that many of the same members are on multiple forums but not all members are them same. I'm just hoping for enough input from other folks to give me an understanding of something I've been ignorant about all these years.

 

[E. von Hoegh]

Understood... I realize that many of the same members are on multiple forums but not all members are them same. I'm just hoping for enough input from other folks to give me an understanding of something I've been ignorant about all these years.