[Klaus]

Maybe because they both have rather weak STF elements at almost around 1 stop for both while Sony is at 2 stops.

 

But you are saying Fuji and Laowa don't show that diffraction effect at all?

 

Well, look at the MTF charts ... I don't see anything special there in terms of overall characteristic.

[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.

[Klaus]

@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. 

[obican]

Well, look at the MTF charts ... I don't see anything special there in terms of overall characteristic.

 

But you've tested the Sony STF on a much higher density sensor, maybe that's why you see the diffraction effects more easily. That's why I suggested to test the Sony on a lower resolution sensor to see what happens. I'd still try to test the old Minolta STF version too.

 

Actually disregard, Fuji APS-C sensor isn't that far behind in density.

[Brightcolours]

@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

[Klaus]

Wim does not know these things.

 

Anyway, here is a discussion about it:

https://www.dpreview.com/forums/post/59063567

 

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.

[Brightcolours]

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?

[wim]

@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