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Zeiss ZM 50 f/2 on mFT
#1
Hi Klaus,



Thanks for this review. I'm looking in to M mount lenses to use on my Sony Nex.



I found an interesting result and a comment in the [url="http://www.opticallimits.com/olympus--four-thirds-lens-tests/469-zeiss_zm_50_2_43?start=1"]ZM 50/2 review[/url] and wish you could explain it a bit more...



First the vignetting characteristic of this lens is very very good at 0.38 stops at f/2. For example the Panasonic Leica Macro-Elmarit 45mm f/2.8 is [url="http://www.opticallimits.com/olympus--four-thirds-lens-tests/490-leica_45_28?start=1"]1.22 stops wide open[/url]. And the ZM 50/2's review also confirms this by saying:



Quote:As a full format lens it has an easy play on micro-4/3 cameras when it comes to vignetting. Even at f/2 it's nothing to worry about in real world situations.





What I'm puzzled by is the comment you made regarding the lens' wide-open corner resolution figures:



Quote:The Zeiss lens delivers an impressive quality from f/2.8 onwards but it struggles a bit at f/2. It has no problems at max. aperture on the Leica M8 but it seems as if it's not aligned to the LiveMOS (4/3) sensor characteristics.



After seeing mFT and Sony Nex E-mount cameras with significantly closer flange distances than the M mount, I'm very strongly inclined to think that this offset micro-lens tech of Leica is marketing hype and a hack job to deal with the outdated sensors they put in to their digital M bodies.



I can't see, at least for the FourThirds area, how an M mount lens will have difficulties in getting light to hit the sensor than than any other mFT lens. I think the (low) vignetting characteristics confirm this.



Plus I don't think LiveMOS can be blamed here because it's still just a Bayer pattern system with supposed improvements in sensor fill-factor, read-out and built-in NR.



So my question is... does this mean the ZM 50/2 is actually a "bad" lens in the corners when it's wide open? Could it have been something else that was not accounted for in the review like the field-curvature? I've heard lenses like the Noctilux suffer quite a lot from this.



Hope to hear your thoughts on this <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='B)' />



Thanks!



GTW
#2
[quote name='genotypewriter' timestamp='1281454025' post='1647']

Hi Klaus,



Thanks for this review. I'm looking in to M mount lenses to use on my Sony Nex.



I found an interesting result and a comment in the [url="http://www.opticallimits.com/olympus--four-thirds-lens-tests/469-zeiss_zm_50_2_43?start=1"]ZM 50/2 review[/url] and wish you could explain it a bit more...



First the vignetting characteristic of this lens is very very good at 0.38 stops at f/2. For example the Panasonic Leica Macro-Elmarit 45mm f/2.8 is [url="http://www.opticallimits.com/olympus--four-thirds-lens-tests/490-leica_45_28?start=1"]1.22 stops wide open[/url]. And the ZM 50/2's review also confirms this by saying:









What I'm puzzled by is the comment you made regarding the lens' wide-open corner resolution figures:







After seeing mFT and Sony Nex E-mount cameras with significantly closer flange distances than the M mount, I'm very strongly inclined to think that this offset micro-lens tech of Leica is marketing hype and a hack job to deal with the outdated sensors they put in to their digital M bodies.



I can't see, at least for the FourThirds area, how an M mount lens will have difficulties in getting light to hit the sensor than than any other mFT lens. I think the (low) vignetting characteristics confirm this.



Plus I don't think LiveMOS can be blamed here because it's still just a Bayer pattern system with supposed improvements in sensor fill-factor, read-out and built-in NR.



So my question is... does this mean the ZM 50/2 is actually a "bad" lens in the corners when it's wide open? Could it have been something else that was not accounted for in the review like the field-curvature? I've heard lenses like the Noctilux suffer quite a lot from this.



Hope to hear your thoughts on this <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='B)' />



Thanks!



GTW

[/quote]



Field curvature is taken care of in all our tests.



e.g. the Voigtländer 15mm lens is supposed to be a very decent performer when used on the a Leica M6 (film) yet it performs poor on the M9 so there is a sensor dependency somewhere. The Z50 is a much more moderate lens so it SHOULD perform better especially on MFT.

If I had to guess we're primarily talking about the design of the micro-lenses on the sensors possibly in conjunction with the "depth" of the sensitive layer of the (retracted) photo-diodes.
#3
[quote name='Klaus' timestamp='1281457195' post='1648']

Field curvature is taken care of in all our tests.



e.g. the Voigtländer 15mm lens is supposed to be a very decent performer when used on the a Leica M6 (film) yet it performs poor on the M9 so there is a sensor dependency somewhere. The Z50 is a much more moderate lens so it SHOULD perform better especially on MFT.

If I had to guess we're primarily talking about the design of the micro-lenses on the sensors possibly in conjunction with the "depth" of the sensitive layer of the (retracted) photo-diodes.

[/quote]

Yes, that, and the relative thickness of film, which covers up a lot of field curvature problems already, and the fact that silicon also has optical properties, unlike the emulsion used in film. And at certain angles of incidence this really comes into play, especially because about half of the light is reflected back as well (with film that is only about 2-3%).



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 ....
#4
[quote name='Klaus' timestamp='1281457195' post='1648']

e.g. the Voigtländer 15mm lens is supposed to be a very decent performer when used on the a Leica M6 (film) yet it performs poor on the M9 so there is a sensor dependency somewhere.

[/quote]



Thanks for your reply. I have no doubt that the M8 and M9 sensors have trouble (due to their outdated designs) when dealing with light hitting from high angles of incidence, especially on their larger sensor areas. I'm still puzzled how this issue could be there on the more modern and much smaller mFT sensors, especially when there's no sign of this happening when looking at the amounts of vignetting.



As for the Voigtländer 15mm issue on digital M... again I think it's a result of the M sensors being bad. For example, here's the same lens (but in SL mount) [url="http://www.16-9.net/lens_tests/15mm_test1.html"]hack mounted[/url] on 5D MkI and compared against the Sigma 12-24:



http://www.16-9.net/lens_tests/15mm_test1b.html



On the more modern and smaller mFT and Nex APS-C sensors, I expect it to perform even better.





[quote name='wim' timestamp='1281473125' post='1652']

Yes, that, and the relative thickness of film, which covers up a lot of field curvature problems already, and the fact that silicon also has optical properties, unlike the emulsion used in film. And at certain angles of incidence this really comes into play, especially because about half of the light is reflected back as well (with film that is only about 2-3%).

[/quote]



Interesting stuff, Wim... thanks for adding. Like I said to Klaus, I'm still puzzled how none of these are reflected in the vignetting <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/laugh.gif' class='bbc_emoticon' alt='B)' />







GTW
#5
[quote name='genotypewriter' timestamp='1281490119' post='1658']

Thanks for your reply. I have no doubt that the M8 and M9 sensors have trouble (due to their outdated designs) when dealing with light hitting from high angles of incidence, especially on their larger sensor areas. I'm still puzzled how this issue could be there on the more modern and much smaller mFT sensors, especially when there's no sign of this happening when looking at the amounts of vignetting.



As for the Voigtländer 15mm issue on digital M... again I think it's a result of the M sensors being bad. For example, here's the same lens (but in SL mount) [url="http://www.16-9.net/lens_tests/15mm_test1.html"]hack mounted[/url] on 5D MkI and compared against the Sigma 12-24:



[url="http://www.16-9.net/lens_tests/15mm_test1b.html"]http://www.16-9.net/...5mm_test1b.html[/url]



On the more modern and smaller mFT and Nex APS-C sensors, I expect it to perform even better.





Interesting stuff, Wim... thanks for adding. Like I said to Klaus, I'm still puzzled how none of these are reflected in the vignetting <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/laugh.gif' class='bbc_emoticon' alt='B)' />



GTW

[/quote]

The latter I think purely because the 50 is an F/2 to start with, has a relatively narrow AoV, and is not a retrofocus lens...



BTW, looks like 16-9.net had an exceptional 12-24 for testing.... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />



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 ....
#6
[quote name='wim' timestamp='1281514588' post='1667']

The latter I think purely because the 50 is an F/2 to start with, has a relatively narrow AoV, and is not a retrofocus lens...

[/quote]



Not sure how narrow AOV can make things worse. Narrow AOV means the lens is long and therefore the nodal point of the lens is further away from the sensor and doesn't this mean the light hits fairly straight-on (just like in the case with long APS-C lenses being usable on FF than wide APS-C lenses?)



Similarly for the aperture, I think a large aperture lens would have less issues than a small aperture lens because the light doesn't have to bend as much? The only problem would be mechanical vignetting from the rear because the exit pupil won't be a perfect circle when viewed from the far corners.





[quote name='wim' timestamp='1281514588' post='1667']

BTW, looks like 16-9.net had an exceptional 12-24 for testing.... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />

[/quote]



Actually, I've seen exceptionally good performance from that lens... unfortunately the zoom misalignments and sample variations put people off too much. Otherwise, its distortion free and the CA is very very low.
#7
Sorry for the rather short reply, I should have been a bit more clear.



[quote name='genotypewriter' timestamp='1281538488' post='1673']

Not sure how narrow AOV can make things worse. Narrow AOV means the lens is long and therefore the nodal point of the lens is further away from the sensor and doesn't this mean the light hits fairly straight-on (just like in the case with long APS-C lenses being usable on FF than wide APS-C lenses?)[/quote]

Yes, you are right, the larger the AoV, the more vignetting you get towards the edges of the sensor, with one of the reasons being that because the sensitive areas of the site wells are not at the surface of the sensor, but literally in a small well, which means that unless you have a sensor with perfect little lenses over th esites in exactly the right position for a certain AoV, you will miss part of the light. However, I would expect the effect of the cosine rule to have a larger effect with large AoV lenses, IOW, normal optical rules causing the largest part of the effect.



The AoV part also comes into this when light gets reflected of the sensor, or rather of the site well bottom. But that I would expect to cause the infamous fringing effects. towards the sides of a sensor.



Regarding the size of the sensor, well that also has an effect. The larger the sensor, the wider the AoV will be for the same FL, and vignetting is directly, almost exponentially, related to AoV. That's the cosine rule I was referring to above. Whether a lens is designed for APS-C or for FF doesn't matter in this regard, the only dfiference will be the FL number on the lens for a similar AoV.

Quote:Similarly for the aperture, I think a large aperture lens would have less issues than a small aperture lens because the light doesn't have to bend as much? The only problem would be mechanical vignetting from the rear because the exit pupil won't be a perfect circle when viewed from the far corners.

Well, AoV is in principle independent of aperture, so that isn't true, actually. However, there are some designs lately, where, by means of having a separate image projecting part as part of the design in a lens, the light rays are kept as parallel as possible. Still with a distinct AoV, but much less than one would expect from such a lens. In a way this is a modified retrofocus type of design, and AFAIK, really only used in WA lenses so far, which for slrs have to be of a retrofocus design anyway. It may introduc all kinds of other optical problems, however, such as higher barrel distortion levels.



The reason for vignetting at large apertures, apart from the effects of the AoV, is twofold, namely that a barrel doesn't have infinite width, and there also is the effect of light rays refracting differently towards the edges of a lens than they do in the centre, although the first effect is the strongest.



The cats eyes effect in specular highlights, f.e., is actually caused by mechanical vignetting of the lens barrel, and is much more common with large aperture complex lenses than with small aperture simpler lenses (which tend to be a lot shorter in build). That is a very rough generalization, I know, but provided a manufacturer doesn't create an absolute minimalistic design but overdesigns the glass and barrel a little, you should have no more vignetting than optical theory allows for.



There are a few lenses that actually do better in this regard, the new TS-Es come to mind: they do better at least for the unshifted or untilted part of an image ... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />. But then, they aren't very fast lenses either.

Quote:Actually, I've seen exceptionally good performance from that lens... unfortunately the zoom misalignments and sample variations put people off too much. Otherwise, its distortion free and the CA is very very low.


Well, the lack of distortion is IMO the only redeeming feature of that lens, for me anyway. I tested two for half a day, took the best one home, and was horrified by the vignetting in real life shots (at any aperture and FL), the CA, the behaviour with regard to flare and ghosting, and the blur or rather smearing towards the edges and in the corners. The only good part in the images was about a 1/3 crop, ok, maybe a 1/2 crop. And that was the better lens of the two. A third one I tried wasn't any better either.



I exchanged it for a Nikkor 14-24, which is very good, but a little awkward to work with on a Canon body, and later on replaced that with a TS-E 17L, which proved to be even better again and is quite easy to work with. Ok, the Nikkor with G-EOS adapter is twice the price of the Sigma, and the TS-E almost 3X the price, but I guess that is what it costs to get a really good lens in that focal range. So, granted, for the money the Sigma is still very good, as there isn't anything else in its price class, or when you need 12 mm and can't do a two-image shift panorama, but personally, I couldn't live with it. Fortunately, I am fine with 17 mm and the occasional stitched shot <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />.



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 ....
#8
Hmm I'm still puzzled by how resolution can be affected by the angle of incidence without any added vignetting.



[quote name='wim' timestamp='1281541825' post='1678']

Regarding the size of the sensor, well that also has an effect. The larger the sensor, the wider the AoV will be for the same FL, and vignetting is directly, almost exponentially, related to AoV. That's the cosine rule I was referring to above. Whether a lens is designed for APS-C or for FF doesn't matter in this regard, the only dfiference will be the FL number on the lens for a similar AoV.



...



There are a few lenses that actually do better in this regard, the new TS-Es come to mind: they do better at least for the unshifted or untilted part of an image ... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Smile' />. But then, they aren't very fast lenses either.

[/quote]



I'm not sure whether I agree with your first comment because as you said in the last part, a large image circle does help reduce the vignetting. Also there are many examples of the same focal length+max f-number combinations producing different levels of vignetting mainly because of design.





[quote name='wim' timestamp='1281541825' post='1678']

Well, the lack of distortion is IMO the only redeeming feature of that lens, for me anyway. I tested two for half a day, took the best one home, and was horrified by the vignetting in real life shots (at any aperture and FL), the CA, the behaviour with regard to flare and ghosting, and the blur or rather smearing towards the edges and in the corners. The only good part in the images was about a 1/3 crop, ok, maybe a 1/2 crop. And that was the better lens of the two. A third one I tried wasn't any better either.

[/quote]



Yes, it doesn't sound too different from what most people encounter with the 12-24, unfortunately. Not sure if you've seen the review below:



http://www.juzaphoto.com/eng/articles/si...review.htm



IMO, this is not the sharpest sample of the lens I've seen but it's still very good. There was another test from a lesser known guy somewhere on the net which was more of a chart test and the one he had was even more impressive.



GTW
#9
Hi geno,

[quote name='genotypewriter' timestamp='1281974177' post='1815']

Hmm I'm still puzzled by how resolution can be affected by the angle of incidence without any added vignetting.[/quote]

Under normal conditions you get (optical) vignetting simply because the image is stretched out further towards the edges than it is in the centre. Because the image is stretched out, it is logical that the resolution is also affected.



Also, the larger the angle of incidence of light (the more it diverges from the optical axis), the more the light will get refracted, and hence the spectrum of light broken up. This reduces resolution drastically, as it is very difficult to put all wavelengths of light back together again. This is why there generally is both more CA and less resolution towards the edges and corners of a frame then there is in the centre, where light essentially travels parallell to the optical axis of a lens.



However, I don't entirely know what the effect of relatively deep site wells is on reflected light and potentially the image, as reflected light might be refracted by the site well's edges, as well as light getting into the site well. I was speculating about this, to be very honest. I don't know for sure what the ultimate effect is. I do know that this is likely one of the reasons for the CA towards the edges of the frame with UWA lenses, especially non-retrofocal ones. I also know that PF is more apparent with digital than it is with film, which is an indicator that the sensor assembly contributes at least partly to PF. In an area that suffers from PF, the resolution is also a lot less than in surrounding areas. I reckon PF is caused at least partly by reflection or refraction of certain parts of the sensor assembly, and thereby is not only related to high contrast transitions (where it is blatantly obvious), but also to certain angles of incidence in a specific spot on the sensor, and probably to whether PF shows up or not. Again, speculation on my part, however.

Quote:I'm not sure whether I agree with your first comment because as you said in the last part, a large image circle does help reduce the vignetting. Also there are many examples of the same focal length+max f-number combinations producing different levels of vignetting mainly because of design.

That may well be the case here. Do note that I was really trying to speculate why this might be the case. I am very interested in this type of behaviour, because I don't particularly like (extreme) vignetting a lot myself as it also takes away from available DR if you correct it. The lens is rather long for a 50 mm, also because of the two static elements at the back for additional close focus and possibly other corrections. This means a long lens barrel, which may well cause more mechanical vignetting. This may not show up in the same way as with e.g. mechanical vignetting caused by a too small filter, as a lens barrel is completely defocused, but it will likely have an influence, and that influence may be rather large.

Quote:Yes, it doesn't sound too different from what most people encounter with the 12-24, unfortunately. Not sure if you've seen the review below:



[url="http://www.juzaphoto.com/eng/articles/sigma_12-24_review.htm"]http://www.juzaphoto...2-24_review.htm[/url]



IMO, this is not the sharpest sample of the lens I've seen but it's still very good. There was another test from a lesser known guy somewhere on the net which was more of a chart test and the one he had was even more impressive.



GTW

Yes, I have seen Juza's test, and I saw another one as well, not the chart test however. If you look carefully at the detail of the corners/edges in any of the photographs taken with a Sigma EX 12-24, you will notice the smearing of detail, on FF that is. And in high contrast situations, the CA towards the corners is truly of a magnitude you don't want to know about, although that may be caused by the same smearing effect (coma/astigmatism probably).



Do note that the winter landscape photograph Juza shows, has distinct smearing in the detail of the large rocks in the bottom corners. This at F/11, where these should be really sharp. I saw a similar photograph somewhere else, where it was even more obvious, because the person testing the lens also showed 100 % crops of the bottom corners. He was quite happy with it however.



Here are some of my results with the Sigma 12-24, deliberately taken under difficult conditions, whole image first, followed by a 100% crop of the top right corner, which shows its flaws best:



[Image: Sig12-24-02.jpg]



[Image: 12-24-01.jpg]



Do note that this part of the image is well within DoF. Also note the smearing of detail, and the heavy CA. This photograph, and the whole test set I did to which it belongs, really freaked me out, and this was the best lens out of 3 I tried in the shop! It is also why I ended up with a Nikkor 14-24 first (good but awkward to operate if you want to choose a specific aperture other than F/8, wide open or fully closed), followed by a TS-E 17 <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' /> (better than the Nikkor, and probably the sharpest lens I own). And I couldn't be happier, as far as UWA is concerned. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />



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 ....
#10
[quote name='wim' timestamp='1281991861' post='1827']

Under normal conditions you get (optical) vignetting simply because the image is stretched out further towards the edges than it is in the centre. Because the image is stretched out, it is logical that the resolution is also affected.

[/quote]



Hmm, not sure if I can see what you mean here. First of all, I don't think there's any more stretching of the objective plane on a non-retrofocus lens than there is on a retrofocus one.



Secondly, if the non-retrofocus design means the nodal point of the lens sits closer to the image/sensor plane than on a retrofocus design, then it means light has to travel a shorter distance... this should, on the flipside, reduce light fall off (without considering the sensor response w.r.t. AOI).





[quote name='wim' timestamp='1281991861' post='1827']

Also, the larger the angle of incidence of light (the more it diverges from the optical axis), the more the light will get refracted, and hence the spectrum of light broken up. This reduces resolution drastically, as it is very difficult to put all wavelengths of light back together again. This is why there generally is both more CA and less resolution towards the edges and corners of a frame then there is in the centre, where light essentially travels parallell to the optical axis of a lens.

[/quote]



I agree about the high refraction within the lens due to lens design... my question is how can such a lens perform better on film than on digital but show no increases in vignetting on digital?





[quote name='wim' timestamp='1281991861' post='1827']

However, I don't entirely know what the effect of relatively deep site wells is on reflected light and potentially the image, as reflected light might be refracted by the site well's edges, as well as light getting into the site well. I was speculating about this, to be very honest. I don't know for sure what the ultimate effect is. I do know that this is likely one of the reasons for the CA towards the edges of the frame with UWA lenses, especially non-retrofocal ones. I also know that PF is more apparent with digital than it is with film, which is an indicator that the sensor assembly contributes at least partly to PF. In an area that suffers from PF, the resolution is also a lot less than in surrounding areas. I reckon PF is caused at least partly by reflection or refraction of certain parts of the sensor assembly, and thereby is not only related to high contrast transitions (where it is blatantly obvious), but also to certain angles of incidence in a specific spot on the sensor, and probably to whether PF shows up or not. Again, speculation on my part, however.

[/quote]



Maybe we should think about what we haven't really talked about so far... for example film thickness and its role in reducing spherical aberrations, etc. I think even more so the reason is the magnification at which we look at digital images. You wouldn't print a 35mm slide/negative to the size of 86"x57" and look at from 2 feet away even if it was really that good, but every 12MP FourThirds image gets the same magnification on a regular 24" monitor when viewed at 100% <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='Big Grin' />



GTW
  


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