Lens Apertures -- How Round Is Round Enough ?

I'm aware there's some controversy regarding what makes good bokeh... or if such a thing even exists. I don't intend to start a riff. I'm convinced (I know) that lens design and aperture roundness both affect OOF image quality both in front of and behind plane of focus. So, please let's not get into a heated debate over "bokeh". I saw some animus a couple years ago when I asked about bokeh. I posted back then that, IMO, a nice round aperture was as important as lens design regarding pleasant bokeh and a few disagreed. That's okay but, again, let's keep this focused on the image rendering benefits of rounder apertures.

So... how round is round enough?

I just bought a 250mm Imagon in an older Copal #3 shutter that has ten blades (it's not here yet). I'm thinking it's aperture is "round enough" such that it would be very difficult to discern the difference between using the shutter's built-in adjustable aperture vs. using a perfectly round disc insert (outer holes blocked because I don't like the effect). The ten-blade Copal #3 aperture is not as nearly perfectly round as many older apertures with 12-20 blades but it's not bad.

So, what do you think? Is the ten-blade aperture in the older Copal #3 "round enough" that I can use it rather than the slip-on discs (peripheral holes closed) such that I can't tell the difference?

I always wonder about posts like this. Why are you using the aperture blades at all if you want out of focus areas? For example my Zeiss 35mm F2.0 has only 3 blades. I usually only bring them into the light path when I want to minimize or eliminate out of focus areas. Also, on an Imagon the plates have their own round central aperture opening.

He's using the aperture blades as an alternative to the disc insert as a means of adjusting diffusion.

The old copal3 is good. I'd say anything with more than 8 blades is good, but shape of the blades matter.

Shutters/lenses with a minimal amount of blades sometimes render bright reflections as stars.

If a scene is 100% in focus (like a f64 style scene) or with scheimpflug, it's not going to matter, just like on an enlarger lens when you're basically focusing grain not a scene.

jp498 said:

He's using the aperture blades as an alternative to the disc insert as a means of adjusting diffusion.

The old copal3 is good. I'd say anything with more than 8 blades is good, but shape of the blades matter.

Shutters/lenses with a minimal amount of blades sometimes render bright reflections as stars.

If a scene is 100% in focus (like a f64 style scene) or with scheimpflug, it's not going to matter, just like on an enlarger lens when you're basically focusing grain not a scene.

Click to expand...

Precisely correct. In fact, the Imagon I purchased has no discs included so I'll have to make some if I want to use inserts. I won't be closing down more than one or two f-stops. If I want sharp/contrasty images then I'll choose a different lens. I don't want the "star effect" and I don't want OOF areas to be "jittery". I won't be using any Imagon at f64.

Same answer as last time. The shape of the aperture only affects the shape of the OOF highlights, not their nature. It's still the least important factor, behind spherical aberration, apodisation and reflectiveness of the blade edges.

Since you have an Imagon, it's pretty good in that department. Consider the sink strainers that people use; they're a kind of like a dithered/halftoned apodisation filter but they're full of hard edges. If that kind of thing (a highlight point turning into a big disc surrounded by lots of little ones) is acceptable to you, then basically any old aperture will be fine. The 10-blade will be fine.

I would also assert that image content and composition is far more important than blade-counting. I've got some great results from lenses with 5 or 6 blades - you can definitely see the hexagons - but they're not a detraction from the image.

The thing that surprises me is so many pay no attention to OOF areas. I don't always want a bit of chromatic or spherical aberration but I do sometimes want a little in special circumstances. The thing is these distortions are not the same as the distortion created by jagged apertures, which is unpleasant to my eye. This isn't always obvious but it often is. It's most visible when there is more contrast between bright and dark objects in OOF areas.

I don't like the effect of the sink strainer inserts. In fact, in my OP I mentioned this. I'll only be using the inserts with the outer holes closed or just the shutter's built-in aperture... if it's round enough.

Old-N-Feeble said:

The thing that surprises me is so many pay no attention to OOF areas. I don't always want a bit of chromatic or spherical aberration but I do sometimes want a little in special circumstances. The thing is these distortions are not the same as the distortion created by jagged apertures, which is unpleasant to my eye. This isn't always obvious but it often is. It's most visible when there is more contrast between bright and dark objects in OOF areas.

I don't like the effect of the sink strainer inserts. In fact, in my OP I mentioned this. I'll only be using the inserts with the outer holes closed or just the shutter's built-in aperture... if it's round enough.

Click to expand...

That's exactly why so many photographs, which could be outstanding, aren't. The out-of-focus character of a photograph can be very distracting if the lens/shutter being used is not well understood. Also, don't be surprised that so many photographers are not artists, or have little knowledge of what constitutes a "pleasing picture" to others. They know what they like, and nothing else matters. If they own the camera and lens, they have a vested interest in that equipment. Therefore it must be good equipment, regardless of the appearance of the photographic works created using said equipment. But, many kudos to those photographers that "pay attention" to what they are doing. They realize there's a more to the creation of a pleasing photograph than buying just any photographic apparatus.

I use Waterhouse style stops on most of my cameras. Those of course are free of blades. I prefer apertures that are as close to round as possible. I recall counting the blades on one of the shutters recently, and if memory serves it had 17 blades. I recall it being perty round throughout it's range.

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What constitutes pleasing out-of-focus characteristics is a bit involved. I distinguish this subject from "soft focus" pictorial photography per se.
Having multi-bladed apertures is obviously helpful; but it's also a function of lens design. For example, I have four different 360mm lenses for
8x10 film. Most of the time I want everything in focus, but certainly not always. My Fuji A 360 has a modern Copal 1 shutter with just a few
blades, so not a very nice background blur. Utterly superb for most other applications. Then I have a classic Kern Dagor in a multi-bladed 3S
shutter. Give a nicer effect for portraiture, but otherwise not really good random background blur - a bit busy. Then there's an astoundingly
sharp 360 Apo Nikkor dialyte process lens with a wonderful multi-bladed aperture, but distracting "double-lined" background blur. Frustrating. Then I remembered that somewhere I had an old coated Carl Meyer tessar-style process lens with a multi-bladed shutter. Mounted that on
a lensboard and wow! You just never know until you look thru the things at your intended subject matter and working apertures.

Drew... Is it dialyte designs in general you don't like the OOF areas of, or just the Apo Nikkors? Is it Tessar designs in general you prefer the OOF areas of or just the Carl Meyer process lens you have? Have you tried any of the Tessar formula Apo Nikkors?

Interesting question. But I'm certainly not going to go out and collect a whole bunch of lenses I don't need just to find out. Most of these process lenses I acquired free. The Apo Nikkors in particular make superb enlarging lenses and do my repro work, like making enlarged interpositives and internegs. I was thinking about trying a Fuji 420 L tessar formula - heavy, and not an ideal shutter, before remembering I
already had a Carl Meyer tessar. Of course, there are numerous old tessars out there, which portrait photographers already know about and
often pay top dollar for. My Nikkor M taking lenses are modern tessars (the most modern rendition of that design, in fact), but give that fairly
miserable Nikonish double-lined effect, so just optical formula doesn't answer the question. Carl Meyer was of course just a private marketing
label, so I have no idea who actually manufactured the lens. It's modern enough to give a very crisp enlarged print in its own right. Not as
big an image circle as my other 360's, but ample enough for most of my 8x10 applications. I don't own any of the older Apo Nikkors or G-Clarons back when they were made tessar-style. If I stumble on something cheap, I might try. Otherwise, I'm getting old enough myself that
I don't want a lot of unnecessary spares laying around. I'll be doing a steep hill tomorrow with a full pack with the Ries and 8x10, tuning up for a long backpack trip with 4x5. But I've got a solid carbon fiber tripod already in reserve for when I hit my 70's, so I can stay with 8x10
as my primary format awhile longer, at least in terms of day hiking.

Drew... Are you sure it's Nikon's version of the Tessar formula that bothers you or is it the 5 or 7 blade apertures in those newer shutters?

These are really two different issues. The roundness of the aperture determines the shape of the out-of-focus highlights etc. The characteristics of background lines is another issue. I don't want to get into convoluted arguments about what might or might not constitute
ideal "bokeh', but almost everyone agrees that no-no's include conspicuous polygons and double-lines or related distracting rendition of unwanted detail. No different with Nikkor small optics. Most are miserable in this respect, but then they specifically engineered certain items like the fast 85's and defocus-control 105's and 135's for exceptionally pleasing background blur. Most modern view camera lens have given up on that kind of thing, with the exception of a few soft-focus options per se, which is not the same thing. Even with modern plastmats, I find that images taken with my old Schneider Symmar S have more pleasing out of focus rendition than the otherwise superior, sharper,
and more contrasty plastmats which replaced them. Different lenses have different personalities at times. Nice to have choices.