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12-16-2011, 04:02 AM   #46
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The 'onion rings' don't appear as regular as Newton's Rings. They may well be caused by a combination of things such as baffles, lens tubes, lens edges and interference patterns working together and there may not be a singular cause for them to exist. I can see that an aspheric element could have a kind of peak, or corner, in it's curve and as such, at that corner ( a circular ring on the lens surface) that light could be diverted out of the line of sight and as such could appear darker.

Of course I have absolutely no credibility in this matter.

12-16-2011, 04:17 AM   #47
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OK, I checked out the Distagon pic and I say the bands are the edges of the lens elements are causing it because they are new reflectors in the scenario. That upper left 'onion ring' looks like a tube pointing outward at ab oblique angle to the focal plane.. it almost looks like a picture of the actual lens elements.

Last edited by bossa; 12-16-2011 at 04:23 AM.
12-16-2011, 06:40 AM   #48
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QuoteOriginally posted by bossa Quote
I checked out the Distagon pic and I say the bands are the edges of the lens elements are causing it because they are new reflectors in the scenario
are you familliar with Occams razor?

nice theory, however a lot of things have to go wrong with the lens design to make your explanation plausible, and Cosina do not strike me as the kind of manufacturer to make those kind of mistakes. If the bands are as reflective as you suggest than taking an image of anything with bright highlights would cause flare on a scale that would render the final image unrecognisable. And as for lens elements making images of themselves is utterly impossible when taking depth of focus into account. No, I think this effect it is caused by aspherical element manufacturing flaws.
12-16-2011, 08:57 AM   #49
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Who would have thought that a "fun" exercise like this would fill 4 pages of controversy over such a subjective thing as bokeh? I just want to see episode 2 now that I own 2 of the lenses used in episode 1.

12-16-2011, 02:40 PM   #50
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QuoteOriginally posted by Digitalis Quote
are you familliar with Occams razor?

nice theory, however a lot of things have to go wrong with the lens design to make your explanation plausible, and Cosina do not strike me as the kind of manufacturer to make those kind of mistakes. If the bands are as reflective as you suggest than taking an image of anything with bright highlights would cause flare on a scale that would render the final image unrecognisable. And as for lens elements making images of themselves is utterly impossible when taking depth of focus into account. No, I think this effect it is caused by aspherical element manufacturing flaws.
Regardless of Okhams Razor it seems possible for the sum of a system's attributes to manifest in an extreme situation in a single form. If the bands you speak of are the fault of aspheric elements in the lens design then it would seem that there would be one or two bands per element at most and as such more bands should require more elements. This is shear speculation on my part based on no facts or real understanding of optics at this level. Having ground a couple of telescope mirrors,playing around with spherical and parabolic mirrors, I can say that the 'onion rings' we have seen in the pictures supplied remind me of out of focus stars and images of optical tube assemblies where the light from the star is a backlight in such an image. The COC in the supplied pictures could be a an image of the optical and tube assembly in the lenses used.

See the 2nd row of images (down the page) of star images (referring to spherical aberrations) and collimating a Newtonian telescope: FAQ about Collimating a Newtonian telescope

Of course they may have nothing to do with what we are talking about but they do look a little similar.

Last edited by bossa; 12-16-2011 at 02:51 PM.
12-16-2011, 04:46 PM   #51
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QuoteOriginally posted by bossa Quote
Having ground a couple of telescope mirrors,playing around with spherical and parabolic mirrors, I can say that the 'onion rings' we have seen in the pictures supplied remind me of out of focus stars and images of optical tube assemblies where the light from the star is a backlight in such an image. The COC in the supplied pictures could be a an image of the optical and tube assembly in the lenses used.
interesting article, I didn't know newtonian telescopes could be such a pain to work with. However as you stated "Of course they may have nothing to do with what we are talking about but they do look a little similar." just because they look similar doesn't mean that the same mechanism is involved. In a newtonian telescope the optical path light follows is substantially less complex than the path light takes when passing through a camera lens, remember that the refractive indexes of the glass elements used in a lens can be dramatically different, the geometry of the lenses themselves, and take into account that the elements are multi-coated and others may be single coated. Also the internal baffles and barrels inside the lens are painted black, ribbed or covered in felt* to prevent them from reflecting any light.

I have noticed a similar issue I have seen when using lenses with an inordinate amount of dust in them, this dust on the internal elements shows up as dark spots in OOF highlights, one of my old takumar 50mm f/1.4 lenses suffers from this:





Full frame image from a dust infested Takumar 50mm f/1.4 - black point set to 50, contrast set to +100 in LR to amplify the effect

This effect confirms my theory that this phenomenon is caused by imperfections in the lens elements themselves, not by wayward reflections/refractions.

*the internal surface of the rear baffle holding the last element of the FA77 is covered in felt.

Last edited by Digitalis; 12-16-2011 at 10:03 PM.
12-16-2011, 04:56 PM   #52
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Re the dust showing up... this points to what I was saying in that the OOFHL may be an actual picture of the actual lens assembly itself.

My comment about the Newtonian was to try and point to the bit about spherical aberrations mainly.
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