28 Elmarit Asph - What causes this?

[J J Kapsberger]

The star pattern, that is (which I like).

Lens: 28 M-Elmarit Asph.
F-stop: f/8-11?

Spot meter on the sky above the steeple.

 

[murrayatuptown]

Supposedly some sort of diffraction or Fourier Transform phenomenon relate to aperture shape, according to a physics prof I had. I think the diffraction is a physical reality and Fourier Transform is merely a mathematical explanation.

While there are many different aperture shapes (and number of aperture leaves), he alleged odd vs even had the most profound effect of the shape of such phenomena. He said they both produce such things but they are different looking.

I never an across anything in writing discussing more of what he said, however.

Not sure if that helps.

& I am wondering what happens with truly round apertures like old Polaroid cameras and Waterhouse Stop lenses...if star patterns ever appeared with them.


Murray

 

[laptoprob]

Could a more round aperture give the halo all over, full circle? Or as a set of 'UFO's? Similar to flare I guess.

 

[alexz]

Is far as I remember from my SLR days, shooting scences featured by spectacular highlights - such kind of effect is often achieved by small apertures. As per my understanding, small aperture cases a diffraction of the rays entering the pupil.

 

[Meleica]

From photonotes.org:

"Why does it matter how many blades the aperture diaphragm has?

The adjustable aperture diaphragm in most camera lenses consists of a number of flat wedge-shaped metal blades. As you adjust the lens aperture settings these blades rotate in or out, and the aperture opening changes size in an iris-like fashion.

The shape of the hole made by this adjustable diaphragm depends on the number of blades and the shape of the blades. For example, if you have a 5 blade aperture diaphragm then the aperture will be a pentagon in shape. An 8 blade aperture diaphragm will of course yield an octagon.

There are two areas in which this aperture shape affects the final image. First, the shape of lens flare on a photograph is typically governed by the shape of the aperture. You may have seen photographs with pentagonal or hexagonal lens flare, for example, or star-shaped highlight areas in a photograph taken with a small aperture setting. Second, it’s generally held that the closer the aperture is to a circle the smoother out of focus areas (bokeh) tends to be, though it isn’t the only factor contributing to bokeh. Many lenses have at least 6 or 8 aperture blades, frequently with curved edges, to approximate a circular aperture opening for this reason. Canon have in fact started billing some of their recent lenses as having “circular” apertures, indicating near-circular openings."


Hope this helps
Dan

 

[Magus]

Post deleted by posters request

 

[sting-ray]

And that correction, Magus, is hilarious!