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Canon FD 24mm f1.4 L
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PostPosted: Thu May 24, 2012 8:26 pm    Post subject: Concert with canon fd 24/1.4 Reply with quote


Last edited by hoanpham on Sat Jan 02, 2016 12:12 pm; edited 1 time in total

PostPosted: Fri May 25, 2012 1:45 pm    Post subject: Reply with quote

These onion rings are no airy disks.
The onion rings show the manufacturing of the aspherical lens surface.

Airy disks size have maximum brightness in the center - these onion rings at this pictures have a minimum there.
Wikipedia http://en.wikipedia.org/wiki/Airy_disk:
"In optics, the Airy disk (or Airy disc) and Airy pattern are descriptions of the best focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light."
In case these onion rings are the best focused spot, the resolution of this lens would be only ~50 Linepairs per image height.
Airy disks diameter for the first minimum should be maximum ~ pixel size of the camera.
Airy disks are - a bit simplified - the point spread function of our lenses. And the complete image our camera sees, is made of a lot of small airy disks (simplified). So the airy disks better be small - and they are small, smallest with fast lenses wideopen. Here roughly 1.4 m on the sensor.

PostPosted: Fri May 25, 2012 2:00 pm    Post subject: Reply with quote

Thanks alot for the explaination.
I need to dig deeper into this.
Is there any easy book i can borrow from the library to read more about it? Or any text book that not required advance math?

Will modern optical processes remove these marks?

PostPosted: Sat May 26, 2012 12:13 pm    Post subject: Reply with quote

It looks a little soft to me? Or do I need glasses?

PostPosted: Tue May 29, 2012 10:17 am    Post subject: Reply with quote

ZoneV wrote:
These onion rings are no airy disks.
The onion rings show the manufacturing of the aspherical lens surface.

Ok I admit I was off with the Airy disk nomenclature, but sure is closer to real effect than "onion rings". Let's call it "out of focus diffraction pattern" to be more precise. The diffraction though is the same one as one that produces an airy disk.

The information about the pattern that I wrote is true, it shows how well corrected an optical system is. I know this from telescope mirrors, which are a more precisely corrected than camera lenses, all of them are paraboloids (aspherics). Some information about recognising abberations is here: http://www.telescope-optics.net/diffraction_pattern_and_aberrations.htm

PostPosted: Thu May 31, 2012 8:38 pm    Post subject: Reply with quote

I think at telescopes one see the airy disks because of further enlarging the image from the mirror.

"Onion"rings is only a common name, not a real description about how the lens looks like.
I think only on lenses with aspherical elements sometimes (not with every light) onion rings can be seen, for example Samyang 35/1.4, Samyang 85/1.4, Canon FD 85/1.2 FD 24/1.4.
On very well regarded pure spherical lenses one see no onion rings, for example Zeiss 85/1.4 (C/Y), Zeiss 50/1.4, Zeiss S-Planar 60/4, Minolta Rokkor 58/1.2..
I am very sure that the aspherical lens surface is the reason for the "onion" rings. Airy rings from lenses with normal iris are always bright in the center.

hoanpham, Wikipedia is pretty good.
I know no source that has deeper information about bokeh, aspherical lens influence on bokeh and such.