Aperture Blade Numbers

[scrichton]

I have just mounted up 4 lenses was either gifted or bought for peanuts on the eBay mis-spelt list. The panels have proved to be my only expense really.

Anyway.. the process lenses all Agfa Intergons 150/210/270 f9 have 5 bladed apertures and the dallmeyer and zeiss tessar multi-bladed near circular. I have not had much use apart from a few polaroids in the house so far, as my car getting welded a lot, but how much have people seen a difference with the shape of apertures?

I know the wider the lens theoretically the less it should matter, but the Agfa lenses were from a process camera that was cost wise way in excess of anything normally purchased for standard camera use. Like the difference between zeiss still camera lenses and motion lenses. So will it effect the image, other than the OOF shaping?

I would like to note I am asking this as an " out of interest " question, I don't care about LPI or refractive indexes of lenses. Just does this number of blades really matter in truth of daily use?

[Frank Petronio]

I think so, especially in back light situations and scenes that tend towards flare. That's why I shoot my five-bladed apertures wide open as often as I can.

[Ernest Purdum]

Since the AGFA lenses were made for process use, out-of -focus images, which are what are affected by diaphragm shape, would not have been significant to the lens designer or the original user.

You might notice a differnce say in something like an outdoor portrait with trees with many leaves as background out of focus highlights. Other than that, I wouldn't be too concerned.

[scrichton]

thanks guys, the answers I was looking for. I must admit I maily shoot wide open anyway as I take more pictures of people with the lengths I have, failing that I have a super-angulon and the crop tool in PS :-D

[andy bessette]

Anyway.. the process lenses all Agfa Intergons 150/210/270 f9 have 5 bladed apertures and the dallmeyer and zeiss tessar multi-bladed near circular.

I would like to note I am asking this as an " out of interest " question, I don't care about LPI or refractive indexes of lenses. Just does this number of blades really matter in truth of daily use?

Yo,

I would expect these five-bladed lenses to exhibit very harsh bokeh.

best, andy

THERE'S MORE TO OPTICS THAN MEETS THE EYE

[Dan Fromm]

Andy, why?

I ask because there's more to bokeh than specular highlights, which do indeed show as tiny images of the diaphragm.

[andy bessette]

Andy, why?

I ask because there's more to bokeh than specular highlights, which do indeed show as tiny images of the diaphragm.

Yo Dan,

with the process lens the entire plane is expected to be in focus, so there is no consideration given to the appearance of areas beyond the depth of field. When these lenses are used in general photography, especially when shooting near wide open for subject isolation, vast background areas will be out of focus. The bokeh in these areas is affected by the blades of the diaphragm.

Diaphragms having only a few straight-sided blades will be expected to produce the harshest bokeh because of diffraction caused as light is bent around these larger blades. Diaphragms having rounded blades (or numerous straight ones) minimize the effects of this diffraction.

best,andy

[Dan Fromm]

So, Andy, if I shoot wide open so that diffraction is minimized and the diaphragm is out of the way, will I then get good bokeh?

And what's wrong with process lenses anyway? I mean, there are, and I have or have had, heliar types and dagor types ... Tessar types too, come to think of it.

Cheers,

Dan

[andy bessette]

So, Andy, if I shoot wide open so that diffraction is minimized and the diaphragm is out of the way, will I then get good bokeh?

And what's wrong with process lenses anyway? I mean, there are, and I have or have had, heliar types and dagor types ... Tessar types too, come to think of it.



Yo Dan,

WHOA!

You are completely mistaken if you presume I mean to condemn process lenses in photography.

With regards to your rhetorical question, you will simply have eliminated the aperture blades as a potential problem, so you will get whatever bokeh that lens produces. Are you asking this because you do not believe the blades affect bokeh?

best, andy

THERE'S MORE TO OPTICS THAN MEETS THE EYE

[Dan Fromm]

Andy, I've already pointed out that out-of-focus specular highlights are rendered as images of the aperture. This is why nearly all mirror lenses render oof highlights as rings.

Surely there's more to bokeh, whatever that means to you, than rendition of out-of-focus highlights. Please explain more fully what you mean by bokeh and what influences it.

[andy bessette]

Andy, I've already pointed out that out-of-focus specular highlights are rendered as images of the aperture. This is why nearly all mirror lenses render oof highlights as rings.

Surely there's more to bokeh, whatever that means to you, than rendition of out-of-focus highlights. Please explain more fully what you mean by bokeh and what influences it.

Yo Dan,

once again, as you have ignored the question posed in my last post, I must assume you have your own hidden agenda. If that agenda is to defend your use of process lenses in photography, relax.

There is no way to accurately judge a lens's bokeh by looking only at the brand, design type, or number of aperture blades--one must look at the image created by that lens. However if I were looking for a lens possessing the best bokeh, I would look first among favored portrait lenses, not process lenses. Why? Because the process lens' designer was not concerned about bokeh. This is only what I would do. But if you happen to know of some ringers, please share.

best, andy

THERE'S MORE TO OPTICS THAN MEETS THE EYE

[Ole Tjugen]

The shape of out-of-focus highlights is controlled mostly by the number of aperture blades, but the rendition of the same highlights is controlled more by the amount of residual aberrations.

Most long telephoto lenses for 35mm (and DSLR) cameras demonstrate this very clearly: The background is softly blurred, but anything unsharp in the foreground shows "double tramline-bokeh". This is by design - these lenses are made for distant subjects, and the photographer has more opportunity to avoid unsharp foregrounds than to move a distant mountain.

Portrait lenses have some of the same design criteria: Soft smooth background, and there had better not be a foreground. So the lens makers have made sure that the background is softened by undercorrecting the spherical aberrations.

Process lenses have completely different design criteria: A flat object is to be reproduced as exactly as possible with as little distortion as possible. Softness of the background is not considered at all, since flat subjects have no background. So some are nice, some are harsh - regardless of the number of aperture blades.

[Dan Fromm]

Thank you, Ole.

Andy, I don't have a hidden agenda. But I find much that you've written in this thread wrong or incomprehensible.

[andy bessette]

Portrait lenses have some of the same design criteria: Soft smooth background, and there had better not be a foreground. So the lens makers have made sure that the background is softened by undercorrecting the spherical aberrations.

Process lenses have completely different design criteria: A flat object is to be reproduced as exactly as possible with as little distortion as possible. Softness of the background is not considered at all.

Yo Ole,

thank you.

best, andy

THERE'S MORE TO OPTICS THAN MEETS THE EYE