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08-05-2017, 06:54 AM
(This post was last modified: 08-05-2017, 06:55 AM by Brightcolours.)
I think it is a combined effect of the apodization element sitting further away from the image plane, and the Sony one being stronger and more gradual, the 2nd diffracting more light and the 1st spreading the diffracted light more.
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@Wim - Regarding the "graduated aperture" - is that even possible ?
Diffraction does only occur at the edge of materials that have a different refraction index, doesn't it ?
I have a hard time to believe that the APD element has a variable refraction index.
THAT BEING SAID - when looking at the bokeh highlights - the effect is only extreme (and I mean really extreme) at f/2.8. It is already massively reduced 1/3 stops down. That could indicate that the APD element does indeed consist of two different segments - with the outer ring having a very different refraction index.
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Quote:@Wim - Regarding the "graduated aperture" - is that even possible ?
Diffraction does only occur at the edge of materials that have a different refraction index, doesn't it ?
I have a hard time to believe that the APD element has a variable refraction index.
THAT BEING SAID - when looking at the bokeh highlights - the effect is only extreme (and I mean really extreme) at f/2.8. It is already massively reduced 1/3 stops down. That could indicate that the APD element does indeed consist of two different segments - with the outer ring having a very different refraction index.
Wim does not know these things.
Anyway, here is a discussion about it:
https://www.dpreview.com/forums/post/59063567
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08-05-2017, 11:51 AM
(This post was last modified: 08-05-2017, 11:54 AM by Brightcolours.)
Quote:Still doesn't explain why this only applies to this Sony lens. Even the old Sony 135mm f/2.8 T/4.5 didn't show that behavior (to this degree) - although to be fair - that was on 24mp and not on 42mp.
The Minolta 135mm f2.8 (T4.5) STF did not use the same apodization element, it did not have T5.6 but T4.5, and the element did not sit that far from the aperture?
And yes. sharpening skewing the MTF results a bit which has become more clear with the higher res. sensors also makes comparing results a bit difficult/pointless, in this case?
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08-05-2017, 08:10 PM
(This post was last modified: 08-05-2017, 08:12 PM by wim.)
Quote:@Wim - Regarding the "graduated aperture" - is that even possible ?
Diffraction does only occur at the edge of materials that have a different refraction index, doesn't it ?
I have a hard time to believe that the APD element has a variable refraction index.
THAT BEING SAID - when looking at the bokeh highlights - the effect is only extreme (and I mean really extreme) at f/2.8. It is already massively reduced 1/3 stops down. That could indicate that the APD element does indeed consist of two different segments - with the outer ring having a very different refraction index.
Who knows ....
I need to look at the formulas for a while, as it does sound in a way like a graduated aperture indeed.
In principle diffraction is based on slit-like aperture transitions, IOW, a sharp edge going straight from light to dark. I do not know whether there is an element involved that may affect diffraction when there is not a sharp transition, but a graduated one. It could well be; I've never looked into this type of behaviour in any detail.
In addition, I do not know how the APD element(s) are implemented, whether they still work at F/11, or whether it is a single fixed element of which more and more of the APD effect gets excluded by the actual diaphragm when stopping down.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....