(11-19-2018, 10:25 AM)obican Wrote:(11-18-2018, 02:58 PM)you2 Wrote:(11-18-2018, 12:29 PM)Klaus Wrote: Well, it is just a 50mm lens so you have to get fairly close for a real shallow DoF.
And yes, it seems darn sharp - at least at 30mp (which is not a lot these days)
There is a zeiss paper that talks about this aspect of lens design. For a given focal length (50, 80, ...) the lens design can play a significant factor in the total blur in foreground/background. The net summary is not all xxmm lens are created equal in this aspect. However, it can be tricky to design a lens to meet different objects (clean bokeh, high bokeh, high resolution). The paper didn't really go into that aspect it just explained in detail why different lenses of the same focal length had different amount of blurring.
DOF only depends on two things, Magnification and Aperture. So, lens design apart from these two factors shouldn't create any difference in DOF. Total background/foreground blur is something different but then even then only depends on the Magnification and Aperture. You can't change sensor size, lens design, amount of glass, number of blades or anything else and expect a difference in the amount of DOF / background blur without touching those two variables.
That was the argument that trigger someone digging out the paper. That optical design can in fact play a role in actual DOF for two lenses with the same focal length and aperture can have different DOF. I believe the details were along the lines that DOF is defined as the area from the point of focus that retain focus and by bending the light at sharper angels you can change this area.
(11-18-2018, 03:41 PM)Brightcolours Wrote: Can you find that paper again? In my (Probably failing in this case) memory the paper seemed to just make the proposition without any actual explanation or substance?
If I find it later I'll follow up with a link. I couldn't find it last night. I know it was at least 10 years ago (not one of the newer papers); and the person presented it (dug out the link) in one of the many DOF arguments. My recollection, which is not exact since I only skimmed the paper many years ago, is that it presented two real lenses and showed how one have a higher degree of bending the rays to change the area of DOF.