Importance of aperture shape?

blockend · Oct 3, 2015

I recently bought a box of compact cameras, mostly 80s and 90s varieties, and in the course of testing them was surprised how many had square or triangular aperture blade openings. How much does the shape of the aperture matter to the overall image?

Sewin · Oct 3, 2015

Bokeh would be affected.

blockend · Oct 3, 2015

Sewin said:
Bokeh would be affected.

It would if the aperture was wide enough, but as most are auto exposure cameras with a maximum aperture of 2.8 or 3.5, and typically shoot at 5.6 or higher, I'm wondering if the shape of the opening has a perceivable effect on image sharpness or resolution across the range?

Gerald C Koch · Oct 3, 2015

Considering the quality of the lenses in these cameras the aperture shape is not that important.

Oren Grad · Oct 3, 2015

Gerald C Koch said:
Considering the quality of the lenses in these cameras the aperture shape is not that important.

Many compact cameras that are considered optically quite respectable have odd iris shapes. Grabbing a few cameras from my user-collection just now, my Olympus 35RC, Olympus XA and Minox 35GL all have irregular iris shapes that change in interesting ways with aperture setting. I'm sure I'd find more if I dug further.

Any effect on MTF (resolution/contrast) would be subtle at best, and short of remounting the glass in a shutter with a different iris shape there'd be no way to isolate and measure it. However, under some circumstances these odd iris shapes can have visible effects on the rendering of out of focus areas.

ic-racer · Oct 3, 2015

blockend said:
I recently bought a box of compact cameras, mostly 80s and 90s varieties, and in the course of testing them was surprised how many had square or triangular aperture blade openings. How much does the shape of the aperture matter to the overall image?

Usually has little or no effect. Wide-open images, of course won't show any effects of the blades. When stopped down, the circles of confusion become small and difficult to tell if round or not. Of course, once you get the cameras you can see for yourself.

RobC · Oct 3, 2015

compact cameras tend to have shorter focal lengths and shorter focal lengths tend to have much greater DoF and therfore bokeh only comes into it when focus is on close subjects.

p.s. circle of confusion is smaller at wide apertures in the focal plane. Its bigger at smaller apertures. (resolutoin is greater the wider the aperture. See "rayleigh limit"). DoF is greater but actual resolution is less as you close down lens.

Sirius Glass · Oct 3, 2015

Sewin said:
Bokeh would be affected.

+1

blockend · Oct 3, 2015

As the cameras are from major manufacturers like Nikon and Canon, I'm assuming the shape of the light entering has no discernible effect on image quality. Some have f2.8 maximum aperture and four or six element lenses, so not semi-disposable quality, just simple aperture shapes.

thuggins · Oct 5, 2015

Oly's Trip 35 has a square aperture. I recall reading somewhere that aperture shape has no impact on image quality.

Slixtiesix · Oct 6, 2015

The shape of the aperture can have an impact if you have isolated highlights in the frame that are out of focus, e.g. shooting backlit branches of a tree, or lighting chains on christmas decorations, or something. In those cases the highlights will adapt the shape of the aperture.

Importance of aperture shape?

Privacy & Transparency

Privacy & Transparency