75 Summilux Quandary

[tom0511]

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Interesting. I find the way of transition between focal plane and background a very important one and I do confirm that lenses of same focal length at same f-stop can show different behaviour.

I also think sensor size plays a big role. Abrupt transition between very sharp focused plane and background makes life more difficult IMO. Slightest missfocusing leads to problems, als if you choose too narrow DOF/f-stop it can look ugly.

So I find this factor quite important for some sort of subjects (portraits for example)

[pico]

The images show the speed of in to out of focus. Older lenses usually being more gradual. I'd say you can see the f1.4 is a narrower DOF, with a much slower transition to out of focus. This slower transition often (for me) gives a  are natural look to the Bokeh

 

Agreed. When the OOF behind the subject is particularly abrupt, thus harsh, then I consider the lens to be over-corrected for spherical aberration. It's ugly to me, and seems to be the direction Karbe has chosen. Each to his own. I'll take Mandler's designs.

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[pgk]

Agreed. When the OOF behind the subject is particularly abrupt, thus harsh, then I consider the lens to be over-corrected for spherical aberration. It's ugly to me, and seems to be the direction Karbe has chosen. Each to his own. I'll take Mandler's designs.

 

I suspect that its the use of aspheric elements which do this as a byproduct of ('over'  ) correcting spherical aberration around the point of focus. I equally suspect that this is the reason for less pleasant bokeh, to some extent at least. Interestingly I've been out today shooting with a mix of Karbe and Mandler lenses. At mid to small apertures the Karbe designs are immaculate in their precise accuracy of representation of all in-focus information, whilst the Mandler are not quite so 'precise' but are 'smoother' and still yield fine detail, but not quite as obviously. Both designers produce(d) fabulous lenses though, but I do think that each has its place and depending on subject matter can have its 'drawing' reinforced at times. I particularly like Mandler designs used 'contra jour' when they can really work very well indeed.

[lct]

Not sure what focus rulers may prove but according to this one (Datacolor SpyderLenscal), the Summilux 75/1.4 (middle) seems to be softer in the foreground and sharper in the background than the Summicron 75/2 (right) at f/2. At f/1.4 (left), the Summilux looks generally softer but seems to retain the same kind of bokeh if anything. FWIW.

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[NB23]

So, again, it's all physics.

Less front, so more behind.

More front, so less behind.

 

All in all, same dof at same settings.

Edited September 30, 2016 by NB23

[pgk]

Not sure what focus rulers may prove but according to this one (Datacolor SpyderLenscal), the Summilux 75/1.4 (middle) seems to be softer in the foreground and sharper in the background than the Summicron 75/2 (right) at f/2. At f/1.4 (left), the Summilux looks generally softer but seems to retain the same kind of bokeh if anything. FWIW.

 

My perception is that the middle image has the greatest dof of the three by a narrow margin, or perhaps because of the bokeh, or whatever. But I agree that a test using a B&W target does not represent actuality. I'd hazard the guess that the perception of dof is more complex than a simple mathematical formula can indicate and has a lot to do with soft transitions and conveying details which, whilst they may not be clear, still provide brain processable data. We could go on and on so all I will say is that I'm sure that not all lenses are equal and that dof is a simple concept which is in reality far more complex than we often think.

[lct]

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I don't see any DOF difference in my snaps above either. Bokeh is another story.

[pgk]

I don't see any DOF difference in my snaps above either. Bokeh is another story.

 

Bokeh affect dof because your perception of what is sharp depends to an extent on its 'blurring shape'. The transition between what clearly is sharp, what you can make out and understand, and what is oof is not as simple as our naive notion of a circle of confusion because we actually photograph and view complex shapes (and in full colour which is why set charts are of limited use).

[lct]

Bokeh affect dof because your perception of what is sharp depends to an extent on its 'blurring shape'. The transition between what clearly is sharp, what you can make out and understand, and what is oof is not as simple as our naive notion of a circle of confusion because we actually photograph and view complex shapes (and in full colour which is why set charts are of limited use).

 

Well I'm no techie at all but as i understand it, DoF is a distance based upon focal length, aperture and circle of confusion (CoC). DoF remains the same as long as those factors remain constant. But DoF changes in case of CoC variation due to different film or sensor format, visual acuity, viewing distance, etc. Your "non naive" notion is taken into account by such a variation i guess but i may be wrong.

[pgk]

Well I'm no techie at all but as i understand it, DoF is a distance based upon focal length, aperture and circle of confusion (CoC). DoF remains the same as long as those factors remain constant. But DoF changes in case of CoC variation due to different film or sensor format, visual acuity, viewing distance, etc. Your "non naive" notion is taken into account by such a variation i guess but i may be wrong.

 

Actually (and unfortunately I can't find a link) Zeiss have written an explanation about dof variation based upon lens design.

[michaelwj]

Well I'm no techie at all but as i understand it, DoF is a distance based upon focal length, aperture and circle of confusion (CoC). DoF remains the same as long as those factors remain constant. But DoF changes in case of CoC variation due to different film or sensor format, visual acuity, viewing distance, etc. Your "non naive" notion is taken into account by such a variation i guess but i may be wrong.

Increased spherical (or other) aberrations reduce the sharpness in the plane of focus. The result is that there is a larger depth of sharpness that is not different to the plane of focus, therefore the dof appears to extend further. So it is a way a variation in visual acuity.