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Archive 2014 · When does Zeiss see it fit to use anomalous partial dispersion glass?

  
 
Rodluvan
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p.1 #1 · p.1 #1 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Why does Zeiss put anomalous partial dispersion glass in eg ZF2/35 but not 2/28?

Seeing that both are of Distagon design and fairly similar in most aspects.
Is it simply a decision made on the basis of cost (deliberately making 2/28 less lavish) or does the slight difference in lens design and FL introduce fundamentally more aberrations in the 2/35 that forces them to compensate using such glass?
From what I can tell it has little, if anything, to do with FL as they use it both the 2.8/15 and 2/135 as opposed to asphericals that is predominately (exclusively?) used in wide angle lenses.



Feb 17, 2014 at 03:21 AM
Rodluvan
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p.1 #2 · p.1 #2 · When does Zeiss see it fit to use anomalous partial dispersion glass?


No one?


Feb 17, 2014 at 01:11 PM
Jman13
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p.1 #3 · p.1 #3 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Unless you get a Zeiss design engineer in here, I highly doubt anyone can definitively answer the question. There can be speculation, but hard answers would have to come from Zeiss.

My guess is they were able to acheive the design goals on the 28/2 without using that type of element, whether those goals have a lower standard of correction or a lower target price, I couldn't say.



Feb 17, 2014 at 01:41 PM
LightShow
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p.1 #4 · p.1 #4 · When does Zeiss see it fit to use anomalous partial dispersion glass?


I have to agree, we won't know why unless someone from Zeiss comments on it.
Generally they will use what material they need to to simplify the design, using exotic glass can possibly permit them to reduce the number of elements or the element can be of a less complex design and much easier to grind.



Feb 17, 2014 at 02:29 PM
JonPB
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p.1 #5 · p.1 #5 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Rodluvan wrote:
...the slight difference in lens design and FL introduce fundamentally more aberrations in the 2/35 that forces them to compensate using such glass?


I would say "different" rather than "more." As you note, aside from the 2nd element in the 35/2 replacing the 2nd and 3rd elements in the 28/2, the basic layout appears to be much the same. The rest of the elements have visibly different curvatures, however, and we don't know what kinds of glass they're made of. Likely, the stronger refraction of the wider lens meant that spherical aberrations, distortion, or field curvature were a larger concern than with chromatic aberration in the 35/2. The MTF curves suggest that the 28/2 has more field curvature as it is, and it has a mild moustache distortion whereas the 35/2 is relatively linear.

At any rate, Zeiss decided that the APD element was optimal in the 35 and not in the 28. I'd hardly say that the 28/2 is less lavish, as it costs more than the 35/2--which may be entirely due to the mechanical complexity of mounting the second and third elements properly, whereas the 35/2 only mounts one element in their stead.

Cheers,
Jon



Feb 17, 2014 at 03:39 PM
Steve Spencer
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p.1 #6 · p.1 #6 · When does Zeiss see it fit to use anomalous partial dispersion glass?


I will offer my speculation, so take it with a grain of salt. The 28 f/2 is clearly based on the C/Y mount 28mm f/2, so Zeiss was working with an existing design when they made the 28 f/2 for the ZE/ZF mount. The first lenses that they introduced in this series were predominantly based on these older designs and did not include APD elements (e.g., 50 f/1.4; 85 f/1.4). The 35 f/2, IIRC, came out a bit later and there is no C/Y mount version of it (C/Y had a 35 f/1.4 and 35 f/2.8), so it seems they developed a new lens from scratch. The newer lenses in the series started incorporating APD glass, so as they developed a new design it must have made sense to include that element.


Feb 17, 2014 at 05:03 PM
j.liam
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p.1 #7 · p.1 #7 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Steve Spencer wrote:
I will offer my speculation, so take it with a grain of salt. The 28 f/2 is clearly based on the C/Y mount 28mm f/2, so Zeiss was working with an existing design when they made the 28 f/2 for the ZE/ZF mount. The first lenses that they introduced in this series were predominantly based on these older designs and did not include APD elements (e.g., 50 f/1.4; 85 f/1.4). The 35 f/2, IIRC, came out a bit later and there is no C/Y mount version of it (C/Y had a 35 f/1.4 and 35 f/2.8), so it seems
...Show more

Interesting theory. The Z* 21 is based on the early CY design, retaining most of its characteristics. Does it contain special glass?



Feb 17, 2014 at 05:31 PM
v_deakin
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p.1 #8 · p.1 #8 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Of course, there is the little matter of a Distagon 35/2.0 from the Contarex line sprung to life well before its C/Y siblings.


Feb 17, 2014 at 05:48 PM
Steve Spencer
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p.1 #9 · p.1 #9 · When does Zeiss see it fit to use anomalous partial dispersion glass?


j.liam wrote:
Interesting theory. The Z* 21 is based on the early CY design, retaining most of its characteristics. Does it contain special glass?


Yes it does and a lot of it, but the 21 came later than the 28, 50P, & 85P, and I think I recall Toothwalker saying that the C/Y version also had special glass that could no longer be used because of environmental reasons (perhaps lead?), so perhaps the APD elements replaced the non-environmental glass of the C/Y version.



Feb 17, 2014 at 09:15 PM
jcolwell
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p.1 #10 · p.1 #10 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Steve Spencer wrote:
Yes it does and a lot of it, but the 21 came later than the 28, 50P, & 85P, and I think I recall Toothwalker saying that the C/Y version also had special glass that could no longer be used because of environmental reasons (perhaps lead?), so perhaps the APD elements replaced the non-environmental glass of the C/Y version.


Sounds like the glass used in the Canon EF 200/1.8L. Of course, it's not so much what's actually in the glass, it's the process that's used to make the glass, and what happens to the waste from that process.



Feb 17, 2014 at 09:19 PM
Steve Spencer
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p.1 #11 · p.1 #11 · When does Zeiss see it fit to use anomalous partial dispersion glass?


v_deakin wrote:
Of course, there is the little matter of a Distagon 35/2.0 from the Contarex line sprung to life well before its C/Y siblings.


Yes there was a 35 f/2 Contarex lens, but are you suggesting the ZE/ZF 35 f/2 is in some way a modification of that design? They seem quite different to me, but maybe I am missing something. They do have the same number of elements, but not the same number of groups and they look nothing alike. I would love to know more if there is a connection between the design of these two lenses.



Feb 17, 2014 at 09:30 PM
v_deakin
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p.1 #12 · p.1 #12 · When does Zeiss see it fit to use anomalous partial dispersion glass?


I've no idea, Steve, what, if anything, got passed from Contarex to later ZE/ZF Distagons. I simply meant that there was a precedent for a 2/35 Distagon like there was for a 2/28.


Feb 17, 2014 at 09:53 PM
Keith B.
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p.1 #13 · p.1 #13 · When does Zeiss see it fit to use anomalous partial dispersion glass?


When lead glass is disposed of, it can leach lead into water once it's crushed in a landfill.
I have read years ago that the CY 35/1.4 is inherited from the Contarex days.
I've had both the ZF 35/2 and 28/2 for several years, on both Nikon D3 and D800 cameras.
While both are very good lenses at large object distances and optimum apertures, the 35/2 is the higher performing lens at larger stops(flatter field, I guess) and especially at close range. If I know I'll want to focus at 2' or 1' distance, and have very small detail recorded well, the clear choice is the 35/2.



Feb 17, 2014 at 10:06 PM
jcolwell
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p.1 #14 · p.1 #14 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Keith B. wrote:
When lead glass is disposed of, it can leach lead into water once it's crushed in a landfill....


That's true, but it's not the main problem. What do you think happened to the sludge from the lead-infusing process? Down the drain... Much like pesticide residues going down the river.

It's a good thing that we have more than one Earth.

Oh wait a minute... We only have one. Be mindful.



Feb 17, 2014 at 10:18 PM
Rodluvan
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p.1 #15 · p.1 #15 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Cheers chaps. Like many of you said, I guess all we can do, in the end, is speculate.

What struck me is that the lenses lacking these exotic solutions are generally the lenses considered weakest in the zeiss dsl line up, namely 2.8/25, 2/28, 1.4/50 and 1.4/85. The correlation is 1:1 hinting towards a causality.

So are they weakest by choice or consequence?



Feb 18, 2014 at 03:05 AM
AhamB
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p.1 #16 · p.1 #16 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Keith B. wrote:
When lead glass is disposed of, it can leach lead into water once it's crushed in a landfill.


Aren't lenses grinded using water as a coolant (and as a lubricant when polishing)? That would mean they had leaded water to clean in the first place.

Edited on Feb 18, 2014 at 05:39 AM · View previous versions



Feb 18, 2014 at 03:12 AM
Rodluvan
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p.1 #17 · p.1 #17 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Rodluvan wrote:
Cheers chaps. Like many of you said, I guess all we can do, in the end, is speculate.

What struck me is that the lenses lacking these exotic solutions are generally the lenses considered weakest in the zeiss dsl line up, namely 2.8/25, 2/28, 1.4/50 and 1.4/85. The correlation is 1:1 hinting towards a causality.

So are they weakest by choice or consequence?


Oh, that 50MP doesn't have any either.



Feb 18, 2014 at 05:19 AM
edwardkaraa
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p.1 #18 · p.1 #18 · When does Zeiss see it fit to use anomalous partial dispersion glass?


Rodluvan wrote:
Cheers chaps. Like many of you said, I guess all we can do, in the end, is speculate.

What struck me is that the lenses lacking these exotic solutions are generally the lenses considered weakest in the zeiss dsl line up, namely 2.8/25, 2/28, 1.4/50 and 1.4/85. The correlation is 1:1 hinting towards a causality.

So are they weakest by choice or consequence?


I think Zeiss designers have a predetermined idea of what look they want to achieve with a lens and at what price point. The weakest lenses in the line up are the ones with the most appealing drawing style.



Feb 18, 2014 at 10:10 AM





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