jaapv Posted January 25, 2012 Share #41 Â Posted January 25, 2012 Advertisement (gone after registration) But in a pictorial (as opposed to scientific) photographic context there is only apparent depth of field because depth of field is a visually (not mathematically) assessed criteria. It is most likely that the OP was interested in this, unless there is some scientific application of lenses such as the 28/2......... Yep - we leave the unneccesary over-complicating of things (not that this is very complicated) to non-photographers Link to post Share on other sites More sharing options...
Advertisement Posted January 25, 2012 Posted January 25, 2012 Hi jaapv, Take a look here DOF for ASPH. I'm sure you'll find what you were looking for!
01af Posted January 25, 2012 Share #42 Â Posted January 25, 2012 But in a pictorial [...] photographic context there is only apparent depth of field because depth of field is a visually [...] assessed criteria. It is most likely that the OP was interested in this ... Sure. But it is still wrong to say, "with various lens designs, apparent depth-of-field may change but technically it's always be the same." Â Instead, apparent DOF changes, and technical DOF changes, too, so apparent DOF changes even more. Link to post Share on other sites More sharing options...
pgk Posted January 25, 2012 Share #43 Â Posted January 25, 2012 Instead, apparent DOF changes, and technical DOF changes, too, so apparent DOF changes even more. :eek:! Link to post Share on other sites More sharing options...
jaapv Posted January 25, 2012 Share #44 Â Posted January 25, 2012 :eek:! Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted January 25, 2012 Share #45 Â Posted January 25, 2012 The sensor/AA filter/sensor sites also has a big influence on how a given lens renders and that can also lead to a small change in perceived depth of field for that camera/lens. Â Also some 'not so sharp' lenses even with a tendency to CA, can look better on low MP sensors compared to high MP sensors of same size Link to post Share on other sites More sharing options...
01af Posted January 25, 2012 Share #46 Â Posted January 25, 2012 Also some 'not so sharp' lenses even with a tendency to CA, can look better on low MP sensors compared to high MP sensors of same size. A common misconception. When you define "look better" through the quality of the picture taken with the lens-and-sensor combo then it can never look better on the sensor with the lower pixel count. Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted January 25, 2012 Share #47 Â Posted January 25, 2012 Advertisement (gone after registration) A common misconception. When you define "look better" through the quality of the picture taken with the lens-and-sensor combo then it can never look better on the sensor with the lower pixel count. Â I don't agree. I know for a fact that: A low pixel count sensor don't see/reveal the CA, for some lenses so the image can 'look better' than a high pixel count sensor of same size/pixel pr mm that reveal every fault in the lens. Link to post Share on other sites More sharing options...
lars_bergquist Posted January 25, 2012 Share #48 Â Posted January 25, 2012 In other words: A sensor can have such a low pixel count that it does not record detail that is badly rendered. This is indubitably true. Â Similarly, when seeing a picture with offending detail, you can close your eyes and the picture looks much better. Â The old man who tries to think straight Link to post Share on other sites More sharing options...
DOUG66 Posted January 25, 2012 Share #49  Posted January 25, 2012 Hi, Andy Piper and 01af and the many others interested,  Andy there is no way that I can focus my ancient eyes on something as close as 27.2 mm, my near point is now about 500mm. and with even reading glasses it is about 200mm. I have however set up the experiment as shown in the attached photo. The 10x microscope is set on top of an up ended ice cream container used as light box the M6 camera body with the lens sitting on top of the light box. A leed ring light is mounted on the microscope optics to enable focussing the microscope on the focal plane of the M6 camera. I use this set up for cleaning the sensor of the M8. The lens is frocussed at infinity and the stop set at F2. The exit pupil though slightly out of focus, can then be viewed by the microscope. Results are as follows: The exit pupil of the 35mm ASPH is noticably smaller than the 35mm Series 4 Summicron when both lenses are focussed at infinity and stopped to F2. With the ASPH at F2 and the Series 4 at 2.8 the exit pupils are approximately equal. This would seem to show that the ASPH lens has enhanced DOF. Doug. Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/171240-dof-for-asph/?do=findComment&comment=1908885'>More sharing options...
01af Posted January 26, 2012 Share #50  Posted January 26, 2012 This would seem to show that the ASPH lens has enhanced DOF. No, it doesn't. As I already said—depth-of-field depends on both the size and the position (distance from image plane) of the exit pupil. At infinity focusing, these two parameters always cancel each other out exactly; at shorter focusing distances, size takes precedence over distance but at "normal" shooting distances, the effect still is mostly negligible. Link to post Share on other sites More sharing options...
01af Posted January 26, 2012 Share #51  Posted January 26, 2012 And oh, by the way—when looking at the lens cross-section diagrams in Erwin Puts' Leica Compendium then you can see that the exit pupils' distances for the Summicron-M 35 mm (IV) and Summicron-M 35 mm Asph indeed are significantly different. The former's is approx. 48 - 50 mm; the latter's is approx. 34 - 35 mm. As the exit pupils' sizes must differ by the same factor as their distances, the Summicron-M Asph's exit pupil at f/2 being nearly the same as the Summicron-M (IV)'s at f/2.8 sounds about right. Link to post Share on other sites More sharing options...
DOUG66 Posted January 26, 2012 Share #52 Â Posted January 26, 2012 Thanks for your reply 01af, I I have checked your calculations and I agree with them. I have measured up the physical dimensions of the two 35mm Summicron lenses and it would appear that for the ASPH the exit pupil is slightly less than 7mm in front of the flange which is what I would expect. However in the case of the series IV the exit pupil is 5.25mm behind the front of the lens or aproximately 2.25 mm behind the centre surface of the front element. I find this very hard to accept in the design of a wide angle lens. Do you know how this exit pupil distance was obtained, Was it physically measured or was it calculated by reversing your calculation and assuming no enhancement of DOF. I seem to remember that I had read somewherw that the 50mm Summilux 1.4 did infact exhibit enhanced DOF of aprox one stop, but having searched all day I could not find it again. I do not posess the financial luxury of posessing a pair of Summiluxes or even one to measure it up. Doug. Link to post Share on other sites More sharing options...
01af Posted January 27, 2012 Share #53  Posted January 27, 2012 I find this very hard to accept in the design of a wide-angle lens. There is nothing to 'accept.' It's the way it is, period. In fact, a longer exit pupil distance generally is a good thing because it means the rays forming the corners of the image will hit the sensor at a less oblique angle and thus, reduces natural vignetting. On the other hand, it tends to increase artificial vignetting and requires the rear element to be large, so if you want a fast lens for a bayonet mount with a narrow throat (such as the Leica M bayonet) then exit pupil distance must be short. The Summilux-M 35 mm Asph's exit pupil distance also is about 35 mm, i. e. pretty short.   Do you know how this exit pupil distance was obtained ... No, I don't. I'd say a lens with a negative rear element tends to have a shorter exit pupil distance; with a positive rear element the exit pupil distance will be longer. But that's hardly more than just a rule of thumb ...   ... was it physically measured or was it calculated by reversing your calculation and assuming no enhancement of DOF? Sorry, I don't understand this question. Both size and position of the exit pupil are determined by the lens design.   I seem to remember that I had read somewhere that the Summilux 50 mm did in fact exhibit enhanced DOF of approx. one stop ... I can positively confirm that the Summilux-M 50 mm 1:1.4 Asph has less depth-of-field (and also more background blur) than the Summarit-M 50 mm 1:2.5, at the same aperture and same focusing distance; the difference corresponds to an estimated half or maybe three-quarters of an f-stop (slightly less than one full f-stop). The same is true for the Summilux-M 35 mm 1:1.4 Asph, compared the the Summarit-M 35 mm 1:2.5.  In both pairs, it's always the Summilux that has less depth-of-field. In the 50 mm pair, the Summilux has the wider exit pupil; in the 35 mm pair, the Summilux has the narrower exit pupil, compared to the respective Summarits. So obviously there are more factors affecting depth-of-field (at a given focal length, focusing distance, and aperture) than just pupil magnification. As I said before: Pupil magnification does affect depth-of-field but at regular shooting distances, the effect thereof is insignificant. It will become significant in macro photography only. Other factors—like for instance the degree and the character of the residual lens aberrations, and maybe still others—are more significant. Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted January 27, 2012 Share #54 Â Posted January 27, 2012 I would say that the difference in shooting with a lens that is corrected for flat field, vs. shooting a lens with a curved plane of focus, that difference is much more significant than ASPH vs. Non-ASPH and exit pupil. Link to post Share on other sites More sharing options...
jaapv Posted January 27, 2012 Share #55 Â Posted January 27, 2012 Quite apart from the theoretical discussion of the depth of DOF, it must be emphasized the the subject matter has an influence on the perception of sharpness. A low contrast subject will appear to have a wider zone of relative sharpness than a high contrast subject. Equally the frequency of the subject is important. High frequency parts of the image require more shapness than low frequency ones ( in a portrait critical focus must be on eyes and eyebrows, not the nose, despite the whole face appearing to be "sharp".) I have a feeling this is of more importance than design differences between lenses. Link to post Share on other sites More sharing options...
DOUG66 Posted January 27, 2012 Share #56  Posted January 27, 2012 Hi all, Reasoning that the exit pupil of a lens must be in the same optical plane as the iris diaphragm of the lens otherwise it will cause vignetting, I have measured the optical distance of the diaphragms of the two Summicrons from the film plane. Results:- Series IV 35mm Summicron 46mm ASPH 35mm Summicron 36mm  This would seem to agree with the theory within experimental limits, and I stand corrected. My thanks to all for your patience. Doug. Link to post Share on other sites More sharing options...
01af Posted January 27, 2012 Share #57  Posted January 27, 2012 Reasoning that the exit pupil of a lens must be in the same optical plane as the iris diaphragm of the lens otherwise it will cause vignetting ... ... which isn't true (where did you get this idea from?) ...   ... I have measured the optical distance of the diaphragms of the two Summicrons from the film plane. Results: Summicron-M 35mm (IV) 46 mm ... ... which is wrong ...   ... Summicron-M 35 mm Asph 36 mm ... ... which is wrong again.   This would seem to agree with the theory within experimental limits, and I stand corrected. Obviously you're confusing the lenses. The distance between the physical aperture diaphragm and the image plane is approx. 36 mm for the Summicron-M 35 mm (IV) and approx. 46 mm for the Summicron-M 35 mm Asph—so you got it inverted. In both cases, the exit pupils are not where the aperture blades are. In the former lens, the exit pupil is before the diaphragm; in the latter, behind. In any case, the distance between exit pupil and aperture diaphragm has nothing to do with vignetting. Link to post Share on other sites More sharing options...
Guest #12 Posted January 28, 2012 Share #58  Posted January 28, 2012 And oh, by the way—when looking at the lens cross-section diagrams in Erwin Puts' Leica Compendium then you can see that the exit pupils' distances for the Summicron-M 35 mm (IV) and Summicron-M 35 mm Asph indeed are significantly different. The former's is approx. 48 - 50 mm; the latter's is approx. 34 - 35 mm. As the exit pupils' sizes must differ by the same factor as their distances, the Summicron-M Asph's exit pupil at f/2 being nearly the same as the Summicron-M (IV)'s at f/2.8 sounds about right.  last week you said he writes "heaps of nonsense"... is this an appropriate source? Link to post Share on other sites More sharing options...
01af Posted January 28, 2012 Share #59 Â Posted January 28, 2012 Last week you said he writes "heaps of nonsense" ... is this an appropriate source? For lens cross-section diagrams, I guess it is. After all, he doesn't draw these himself. Link to post Share on other sites More sharing options...
Guest #12 Posted January 28, 2012 Share #60 Â Posted January 28, 2012 For lens cross-section diagrams, I guess it is. After all, he doesn't draw these himself. Â oh, I thought he had some software he complained about Link to post Share on other sites More sharing options...
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