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Archive 2011 · New Zeiss article on the design of wide angle lenses
  
 
philip_pj
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p.2 #1 · p.2 #1 · New Zeiss article on the design of wide angle lenses


Thanks Ed and Tariq, the 24/2 is still quite unknown outside a few users, and few know their gear like you two do. Also of interest is that you both sold your copies, albeit for different reasons, flaws and moving on...I am a manual focus guy these days, can't kick the habit, but a comparison would be very interesting, it would take a Sony person with a ZA24 and a remount 25/2.

I read what Zeiss, who are usually fairly restrained and fact-based in their lens comments, had to say about it back in the early 90s, and it ties in with your comments, bluetsunami:

"All of the possibilities of correcting residual chromatic aberrations were utilised to the full." and "ensures that this new lens delivers superior image quality in all conditions." I'll say. Any lens that gets close to it will be worth looking at, I feel.

25mm is quite a bit narrower than 21mm, more versatile, great at close range...One Ant is also very interested in the difference it will make, probably will not have that 'must get close' vibe of the 21mm, and which really forces its signature look on you, despite the correction. I do a lot at f5.6-8, by which time it should be losing the corner smearing somewhat. We'll see, Jorge's images are not easy to gauge for overall rendering, for me at least.

Does anyone have any idea what the street price is likely to be and the delivery schedule? I saw $1700 somewhere, accuracy uncertain.

Bluetsunami, do you have any web material re the CA-MTF interaction, it seems lenses that lack CA are almost always excellent performers, or is that incorrect?



Dec 08, 2011 at 06:30 AM
Z250SA
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p.2 #2 · p.2 #2 · New Zeiss article on the design of wide angle lenses


Have a look at the MTFs of the Contax 200/3.5 Teletessar with the almost level sagittal and massively sloping tangential curves. Thats the result of heavy lateral CA. Compare it to the Hassy 250mm Superachromat that has no aberrations what so ever. I have both lenses, and the difference is huge. None the less images with the TT can be very nice indeed.


Dec 08, 2011 at 06:57 AM
AhamB
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p.2 #3 · p.2 #3 · New Zeiss article on the design of wide angle lenses


philip_pj wrote:
Bluetsunami, do you have any web material re the CA-MTF interaction, it seems lenses that lack CA are almost always excellent performers, or is that incorrect?


For (ultra)wide angles, that's probably true. Lateral CA is damaging to sharpness.
Tariq had some interesting experiences with different copies of the C/Y Distagon 28/2.8 though (a copy with extreme center sharpness but strong CA in the corners and a copy with less CA, better corners but not the same biting sharpness).


@ZS250: Are you sure the sloping of the tangential curves is causing CA? From looking at the MTFs of different apochromatic supertele lenses, I get the impression that the sloping is normal. For example: http://www.overgaard.dk/pdf/Apo-Telyt-R_280_mm_Technical_Data_en.pdf
When looking at the MTFs of the Canon superteles I see the same. The tangential curve always seems to drop off more when the lens is stopped down. Maybe tangential MTF is affected more by diffraction than sagittal with supertele lenses?



Dec 08, 2011 at 07:38 AM
theSuede
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p.2 #4 · p.2 #4 · New Zeiss article on the design of wide angle lenses


CA does affect the tangential curves in a negative way, but the main reason in a (good) telephoto lens for this behavior is astigmatism.

The "best focus" planes are not identical in sag/mer orientations. This is a normal compromise in the type of constructions you normally use in a longer lens. Ususally it is very hard to optimize for BOTH chromatic error and anastigmatic behaviour. And the chromatic error is much more damaging to the perceivable picture quality (unless the astigmatism is really, really strong...)

You have to differentiate between this and the "best focus achievable". Given an MTF-test where you continually optimize the target distance as picture height increases (allow some optimization for curvature of field) you wouldn't see this behaviour.



Dec 08, 2011 at 09:51 AM
Z250SA
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p.2 #5 · p.2 #5 · New Zeiss article on the design of wide angle lenses


AhamB wrote:
@ZS250: Are you sure the sloping of the tangential curves is causing CA?


Here are two 100% 5D2 crops at f/5.6 from middle far left with the TT and the SA. Yes, Im pretty sure that the LaCA is causing the sloping tangential (vertical branches in the images). Of course there might be components of other As as well as suggested. But the La is pretty strong. I was actually curious about the MTFs of the TT and had to see for myself. Got the SA for pretty much the same reasons. Funspensive, the knowledge digging...















Dec 08, 2011 at 06:50 PM
douglasf13
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p.2 #6 · p.2 #6 · New Zeiss article on the design of wide angle lenses


theSuede wrote:
CA does affect the tangential curves in a negative way, but the main reason in a (good) telephoto lens for this behavior is astigmatism.

The "best focus" planes are not identical in sag/mer orientations. This is a normal compromise in the type of constructions you normally use in a longer lens. Ususally it is very hard to optimize for BOTH chromatic error and anastigmatic behaviour. And the chromatic error is much more damaging to the perceivable picture quality (unless the astigmatism is really, really strong...)

You have to differentiate between this and the "best focus achievable". Given an MTF-test where you continually
...Show more

Hi. In the past, you've mentioned that Leica really isn't using an exceptionally thin IR filter on the M9. Do you know what Leica is doing to preserve sharpness at the edges? Does it mostly come down to the lack of an AA filter? Thanks.



Dec 08, 2011 at 07:23 PM
sebboh
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p.2 #7 · p.2 #7 · New Zeiss article on the design of wide angle lenses


Z250SA wrote:
Here are two 100% 5D2 crops at f/5.6 from middle far left with the TT and the SA. Yes, Im pretty sure that the LaCA is causing the sloping tangential (vertical branches in the images). Of course there might be components of other As as well as suggested. But the La is pretty strong. I was actually curious about the MTFs of the TT and had to see for myself. Got the SA for pretty much the same reasons. Funspensive, the knowledge digging...



that looks like CA is the least of it's problems for the TT.



Dec 08, 2011 at 07:36 PM
bluetsunami
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p.2 #8 · p.2 #8 · New Zeiss article on the design of wide angle lenses


philip_pj wrote:
Bluetsunami, do you have any web material re the CA-MTF interaction, it seems lenses that lack CA are almost always excellent performers, or is that incorrect?


I've only seen it referenced in this particular article (I haven't read that many though), but the lack of CA definitely points to an excellent performing lens especially in the edges and corners with wide angle lenses. The nearly total lack of CA seems to really give a nice sense of accuity or clarity that I think is even appreciable when its really minimized (as apposed to corrected in post) and is probably the main reason why the 2.8/21 Distagon can produce the images its produces.



Dec 08, 2011 at 08:22 PM
wayne seltzer
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p.2 #9 · p.2 #9 · New Zeiss article on the design of wide angle lenses


Zeiss has recently used special glass in both the new 35/1.4 and now the 25/2 to reduce lateral CA to very low levels.


Dec 08, 2011 at 08:43 PM
Z250SA
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p.2 #10 · p.2 #10 · New Zeiss article on the design of wide angle lenses


sebboh wrote:
that looks like CA is the least of it's problems for the TT.


Well, the image was for showing a comparison of LaCA in relation to two very different MTFs. That part is not quite at best focus. The whole image is actually quite nice viewed on full screen 27" iMac, but perhaps too OT to show here in a wide angle discussion.



Dec 08, 2011 at 08:50 PM
 

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sebboh
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p.2 #11 · p.2 #11 · New Zeiss article on the design of wide angle lenses


Z250SA wrote:
Well, the image was for showing a comparison of LaCA in relation to two very different MTFs. That part is not quite at best focus. The whole image is actually quite nice viewed on full screen 27" iMac, but perhaps too OT to show here in a wide angle discussion.


my point was that just because CA is worse on TT and the MTF is also worse doesn't mean that the CA is major cause for the drop in MTF. hard to tell since you say it is misfocused, but it looks to me from your picture as though CA is only playing a minor role in the MTF drop off.



Dec 08, 2011 at 09:38 PM
Z250SA
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p.2 #12 · p.2 #12 · New Zeiss article on the design of wide angle lenses


sebboh wrote:
my point was that just because CA is worse on TT and the MTF is also worse doesn't mean that the CA is major cause for the drop in MTF. hard to tell since you say it is misfocused, but it looks to me from your picture as though CA is only playing a minor role in the MTF drop off.


When you compare the CA around horizontal and vertical branches you see that the vertical has lots of LaCA, the horizontal none. As the vertical corresponds to the tangential curve and the horizontal to the sagittal, Id say that it is indeed the LaCA that does the damage to the tangential curves of the TTs MTF.

Of course I might see "too much" in these very images as I have formed my opinion by comparing a few more images of these lenses as well as others, such as the Contax 180/2.8 Sonnar, 100-300 Vario-Sonnar, some Canons, Hassys 150 and 180, etc. Im actually pretty convinced. So by being wrong I might actually learn something! Must do a star test some day (we have sun set at 3pm these "days").



Dec 08, 2011 at 10:05 PM
sebboh
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p.2 #13 · p.2 #13 · New Zeiss article on the design of wide angle lenses


Z250SA wrote:
As the vertical corresponds to the tangential curve and the horizontal to the sagittal


how's that? where is the crop from on the image? i figured it was fro a corner.



Dec 08, 2011 at 11:26 PM
denoir
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p.2 #14 · p.2 #14 · New Zeiss article on the design of wide angle lenses


Z250SA wrote:
As the vertical corresponds to the tangential curve and the horizontal to the sagittal, Id say that it is indeed the LaCA that does the damage to the tangential curves of the TTs MTF.


Sagittal is in the radial direction towards the center of the image. Tangential is the same orientation as a tangent to a circle around the image the image. It's not horizontal and vertical - it uses a polar coordinate system.



Dec 08, 2011 at 11:46 PM
atran
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p.2 #15 · p.2 #15 · New Zeiss article on the design of wide angle lenses


denoir wrote:
Sagittal is in the radial direction towards the center of the image. Tangential is the same orientation as a tangent to a circle around the image the image. It's not horizontal and vertical - it uses a polar coordinate system.

Could you give an illustration or something? I am quite confused because I remember when I was in school, the polar coordination system is defined by distance between points and an angle (azimuth)



Dec 08, 2011 at 11:55 PM
philip_pj
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p.2 #16 · p.2 #16 · New Zeiss article on the design of wide angle lenses


I recall Andy Piper saying the longer tele Contaxes were not popular because of quite high CA, he felt it was due to lack of ED glass. I have the 100-300mm, like Z250SA, and it shows a very little lateral CA - it has three ED elements.

Shorter (slow) telephoto lenses from that Contax line seem well-behaved in this laCA respect, such as the 85mm and 100mm Sonnars, and like the linked 280/4 Leica Telyt, they show almost identical lower tan lines, most obvious in the 40 lpmm 'fine structure' lines. I assumed that these are well tolerated by lens designers who have bigger problems to address, and thanks to theSuede for the explanation. All these lenses have excellent resolution.

Jorge's images and Zeiss's claims on the lack of CA in the new 25mm seem to indicate that CA can indeed be constrained even with the lens showing some divergence of sag/tan lines for the 40 lpmm set, which you can see in its f4 chart. So maybe it is the ED glass elements doing that job on the CA. They also use both ED elements and Asph surfaces in the less complex ZA 24/2.



Dec 08, 2011 at 11:59 PM
sebboh
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p.2 #17 · p.2 #17 · New Zeiss article on the design of wide angle lenses


atran wrote:
Could you give an illustration or something? I am quite confused because I remember when I was in school, the polar coordination system is defined by distance between points and an angle (azimuth)


correct. the distance is from the center of the frame (the origin on an x,y graph) on a line radiating outward (this is a sagittal line) the distance coordinate in polar coordinates defines a circle of fixed distance from the origin. at any point on the circle you can draw a tangent to it. these represent tangential lines on an mtf.



Dec 09, 2011 at 12:10 AM
wayne seltzer
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p.2 #18 · p.2 #18 · New Zeiss article on the design of wide angle lenses


philip_pj wrote:
I recall Andy Piper saying the longer tele Contaxes were not popular because of quite high CA, he felt it was due to lack of ED glass. I have the 100-300mm, like Z250SA, and it shows a very little lateral CA - it has three ED elements.

Shorter (slow) telephoto lenses from that Contax line seem well-behaved in this laCA respect, such as the 85mm and 100mm Sonnars, and like the linked 280/4 Leica Telyt, they show almost identical lower tan lines, most obvious in the 40 lpmm 'fine structure' lines. I assumed that these are well tolerated by lens
...Show more
How about the Contax N 70-200mm 3.5-4.5 MTF's. How would you compare them to the 100-300 concerning CA?



Dec 09, 2011 at 01:24 AM
philip_pj
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p.2 #19 · p.2 #19 · New Zeiss article on the design of wide angle lenses


Wayne, I confess I have never understood what happened in several of the N class lenses' MTF, especially the zooms. This one you cite has the same 'ED' elements as the late CY zooms like the 100-300mm, but the tan lines are all over the place, like a drunken sailor on his way to the door.

It's odd, since the MTF chart for that 70-200N are very similar to the 'problem' chart in the CZ article this thread is about, to illustrate the effect of symmetrical wide angle lenses on APS-C sensor cameras...people speak very highly of the wide range N mid-zoom, 24-85/3.5-4.5, yet its MTF indicates it should barely work! I once asked a user about it, and he said he 'didn't do MTF', so there...maybe CZ need to revisit these lenses and test them again.

Even the Planar 85/1.4 chart is very strange. Sometime back, one the knowledgable guys here, Toothwalker from memory, said some of Zeiss data on older lenses was something he had knowledge of from CZ, but did not want to publish on the net. Fair enough, I figured they maybe had some type of optical bench glitch...but it got published anyway!



Dec 09, 2011 at 03:02 AM
philip_pj
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p.2 #20 · p.2 #20 · New Zeiss article on the design of wide angle lenses


If you have one, maybe run off a shot of something planar and look at the outer half of the frame, anywhere after 150mm will do, anywhere from wide open to f8. A row of trees with fine branches, 90 degrees to the lens axis would do fine. In good light, this is a tough test for edges/corners definition. CA also, of course.


Dec 09, 2011 at 03:08 AM
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