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Optical design of 1980s Dialyt 8x30

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Old Monday 1st July 2019, 02:37   #1
tenex
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Optical design of 1980s Dialyt 8x30

Can anyone tell me about the optical design (especially number of elements) of the West German 8x30 Dialyt B T* of the 1980s? It really isn't as sharp (etc) as modern roof prisms, even those of the early 1990s like Trinovid BA, and I'm wondering whether the principal reason is the lack of phase coating (as I've previously assumed) or just a design with too few elements, due to limitations of transmission coatings, like any other bino of that period.
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Old Monday 1st July 2019, 04:42   #2
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Originally Posted by tenex View Post
Can anyone tell me about the optical design (especially number of elements) of the West German 8x30 Dialyt B T* of the 1980s? It really isn't as sharp (etc) as modern roof prisms, even those of the early 1990s like Trinovid BA, and I'm wondering whether the principal reason is the lack of phase coating (as I've previously assumed) or just a design with too few elements, due to limitations of transmission coatings, like any other bino of that period.
I'd have to look up the optical design. However, I got an early Dialyt 8x30 BGAT*P (mine wasn't even marked BGAT*P on the pair itself, only on the box) and did a couple of thorough comparisons between it and a slightly older Dialyt 8x30 BGAT*, so I can say with some confidence that the phase coating makes a very clearcut difference, both in resolution and in contrast. In fact, at the time I was more than surprised how large the difference is in reality. I did similar comparisons between a Dialyt 10x40 BGA from the early 1980s, a 10x40 BGAT* and a BGAT*P with similar results.

Since I later got a Trinovid 8x32 BA as well, I can also say with some confidence that there is no difference in resolution between the Zeiss and the Leica. The Leica has higher saturation and is fully waterproof though. The Leica also doesn't have any problems with veiling glare whereas any Zeiss 8x30 is pretty bad in that respect. BTW, the Dialyt 10x40 doesn't have the same problems.

It's these differences that made me get the Leica as well, not the resolution / sharpness or transmission.

Hermann

Last edited by Hermann : Monday 1st July 2019 at 04:47.
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Old Monday 1st July 2019, 12:32   #3
henry link
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Here's a cutaway of the 8x30 Dialyt: cemented doublet objective lens, 4 element Konig eyepiece. A simple design, but nothing obvious there except a lack of phase correction that would prevent it from being sharp in the field center.
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Old Monday 1st July 2019, 14:31   #4
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Thank you both. I don't have a P* version here to compare with, but it's useful to know that the lack of phase coating (confirmed by experiment) is the real issue with this old bino. It's irritating because I bought it in 1989: by then it should have been P*, and I didn't know the difference. Now it's a car or office bino.

The other odd thing about it was that focusing actually moved the objectives, which isn't as smooth or easy as internal focusing. It's still kind of classy, though.
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Old Monday 1st July 2019, 15:55   #5
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Originally Posted by tenex View Post
Thank you both. I don't have a P* version here to compare with, but it's useful to know that the lack of phase coating (confirmed by experiment) is the real issue with this old bino. It's irritating because I bought it in 1989: by then it should have been P*, and I didn't know the difference. Now it's a car or office bino.

The other odd thing about it was that focusing actually moved the objectives, which isn't as smooth or easy as internal focusing. It's still kind of classy, though.
The 10x40B Dialyt focused in the same way, by moving the objectives. Mine always focused smoothly but you need to check the barrel surface that the objective moves over because there tends to be a smear of grease left by the lens and particles can stick to it.

Using the binos at altitude in a pressurised aircraft cabin was mighty strange as it dramatically changed the feel of the focus.

Lee
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Old Monday 1st July 2019, 16:11   #6
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...
The other odd thing about it was that focusing actually moved the objectives, which isn't as smooth or easy as internal focusing. It's still kind of classy, though.
Hello Tenex,

True internal focussing, according to an expert, may actually increases chromatic aberration, although it may be optimised for the middle distance. A floating internal focussing lens would solve the problem.

Happy bird watching,
Arthur
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Old Tuesday 2nd July 2019, 00:08   #7
james holdsworth
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Yep, a world of difference between the P and non P version of this bino.
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Old Tuesday 2nd July 2019, 04:43   #8
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I've had a chance to go through and get into order what I’ve collected about the 8x30 Dialyts, so here goes . . .
(I’ve also made a point of indicating where I’m uncertain as to details e.g. there is some useful but not completely clear data about the early Zeiss roof prisms at the Europa website:
http://www.europa.com/~telscope/czpstwr.txt )

The centre focus 8x30 B Dialyt was offered for just over 40 years! - from 1964 to 2004 (in 2005 it was finally replaced by the 8x32 Victory FL)

Versions
There were 3 different body designs:
- the original 1964 long bodied version (see the page from the 1964 catalogue)

- the first short bodied version from 1969, which resulted in a 100 gram/ nearly 4 oz weight saving (see the attached cross section)

- the second short bodied version from 1987 (?), with the diopter wheel located on the front of the bridge
(see the photo comparing versions 3 and 1, from: https://www.birdforum.net/showthread.php?t=268166 )

In terms of easy visual identification:
- the first two versions had co-located focus and diopter wheels, with the body of the first version being noticeably longer
- and on the 3rd version, in addition to the new diopter wheel location, the rear edge of the bridge angled inwards from the barrels towards the focus knob


Finishes
All 3 versions were available with a leatherette finish, and in addition the 2nd and 3rd versions were also offered in rubber armoured versions
However, judging by the relative numbers of second hand offerings, the RA versions were far more popular than the leatherette ones


Optics
I’ve not been able to obtain the details of the optical construction of the 1st version but there is no reason to imagine that it was more sophisticated than the later versions
- or that it was airtight

The optical construction of the 2nd and 3rd versions is the same - see both the cross-section that I posted of version 2, and that of version 3 provided by Henry in post #3 above
As noted previously on this thread, the design used external focus by movement of the objective lens pair
(this is in contrast to an internal focus system, where the physical length of the optical system - from the front objective lens to the rear eye lens - remains constant during focusing)

continued . . .
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Old Tuesday 2nd July 2019, 04:47   #9
John A Roberts
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continued . . .

Coatings
- the original version had single coated lenses, aka T coating, and silver (?) coating on the 3 non-Total Internal Reflection surfaces of the Schmidt-Pechan prisms

- in 1978, Zeiss introduced multi-coating of lenses, with units marked T* instead of T
multi-coating seems to have been introduced progressively across the product line, with it being added to the 8x30 B Dialyt by 1983

- in 1989, Zeiss introduced phase coating of the 2 roofed surfaces of the prism pair, with units typically marked P or later on P*
(the latter seems to have been done for conformity with the T* marking)
and it seems that phase coating was immediately applied across the Dialyt line including to the 8x30 B
see the 3 images originally from John Dracon, they include then contemporary details both about phase coating and the current specifications
(they're from post #14: https://www.birdforum.net/showthread.php?t=349555 )

- in 1999, Zeiss introduced dielectric coating of the 3rd non-TIR surface of the Schmidt-Pechan prism pair
again it seems that the coating was immediately applied across the Dialyt line - however, there is no marking on a unit to indicate the presence of the coating

As with any premium manufacturer, one would expect that the quality of the Zeiss coatings would have incrementally improved over time
and in support of this, Arek of Allbinos provides 2 graphs detailing changes to the 10x40 version of the Dialyt: https://www.allbinos.com/index.php?art=169


Contemporaneous Alternatives
See my recent post for information about the Leitz and Swarovski alternatives: https://www.birdforum.net/showpost.p...4&postcount=13
- the B version of the Leitz 8x32 was not introduced until 1974, and the rubber armoured version until 1979
- the original Swarovski 8x30 of 1985 did not have a B eyepiece, which was introduced with the airtight Mk II version in 1989
and like the Zeiss, the 8x30 Swarovski was also an external focus design

n.b. Zeiss also made an individual focus version of the 8x30 Dialyt. It was introduced in 1967 and was last listed in the 2004 catalogue
It focused by eyepiece movement and had a smaller Field Of View than the CF version. It's image and specifications are included in the data provided by John Dracon.


John
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Old Tuesday 2nd July 2019, 17:18   #10
tenex
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Quote:
Originally Posted by John A Roberts View Post
the original version had single coated lenses, aka T coating, and silver (?) coating on the 3 non-Total Internal Reflection surfaces of the Schmidt-Pechan prisms...
I thought there was only one mirrored (non-TIR) surface on a SP prism pair. What have I misunderstood?
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in 1989, Zeiss introduced phase coating of the 2 roofed surfaces of the prism pair, with units typically marked P or later on P*...
Interesting PR material there. I always wondered how they handled the issue of having sold (premium!) binoculars that would "cause eyestrain" for decades already.

Thanks also for your chronology. My 8x30 (leather) is the later model with the rear diopter, therefore made just between 1987 and 1988 (when "P" was introduced).
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Old Wednesday 3rd July 2019, 08:02   #11
John A Roberts
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Correction: Only 1 non-TIR surface on a Schmidt-Pechan prism pair

Tenex

You are of course right, there is only 1 non-Totally Internally Reflective surface on a Schmidt-Pechan pair
- the bottom surface on the Pechan prism as indicted in the attached diagram
(and prior to the use of phase coating the 2 roof surfaces were left uncoated)

I'm at a loss as to why I indicated otherwise. I think perhaps I was mindful that there was a total of 3 prism surfaces that could benefit from reflective coatings

Apologies to all


continued . . .
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Old Wednesday 3rd July 2019, 08:03   #12
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Anti-Reflective coating on Schmidt-Pechan prisms

I should add for completeness, that as can be seen from the diagram, the facing surfaces of the two prisms perform both transmissive and reflective functions
- and so can benefit from anti-reflective coating to aid the transmission function
- though with a consequent adverse effect on the reflection function

This is one of the issues that's explored in Konrad Seil's 1991 paper 'Progress in binocular design'
The conclusion is that a single layer coating provides the best balance in performance, see: https://wp.optics.arizona.edu/optome.../Seil-1991.pdf


John

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Old Wednesday 3rd July 2019, 13:11   #13
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At the risk of adding confusion I think it's worth noting that Schmidt-Pechan prisms can be configured in different ways.

The diagram John provided shows an S-P in which the light travels through the prism system in the opposite direction from the way it travels through the Zeiss 8x30 Dialyt cutaways. In the Dialyts light from the objective lens travels first through the Schmidt prism (which in this configuration has the non-TIR mirror coated face) and then through the Pechan prism (which has the roof).

The cutaways below show two contemporary binoculars (Swarovski EL-SV above, Zeiss SF below) that both use Schmidt-Pechans, but with the configurations reversed.
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Old Tuesday 8th October 2019, 10:43   #14
John A Roberts
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I recently came across the following image that complements those in post #8
It compares the leatherette covered v2 and v3 versions of the 8x30

The image is from the auction site Clars: https://live.clars.com/lots/view/1-1...noculars-group


John
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Old Tuesday 8th October 2019, 21:30   #15
Canip
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John,
You write in post #8 that only the third version (1987?) had the diopter wheel at the front.
That design change must have happened much earlier, because my mid - 1970s Dialyt had that design already, see:

https://binocular.ch/wp-content/uplo...-c-705x529.jpg

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Old Tuesday 8th October 2019, 23:54   #16
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Hi Canip,

Looking at the two photos on your site, the particular model is clearly what I describe as the 3rd version
It has both the diopter wheel located on the front of the bridge, and the rear edge of the bridge angled inward from the barrels to the focus knob
(for those interested, the images are from Canip/ Panic’s excellent site at: https://binocular.ch/zeiss-8x30-b-dialyt/ )

As to when the versions were introduced, I based this on the data from Peter Abrahams’ Europa site, see: http://www.europa.com/~telscope/czpstwr.txt
Consistent with the 3rd version's introduction in 1983, the cross-section of the second version in post #8, is from a 1981 Zeiss pamphlet
(and the other images in the pamphlet are also of the second version)

So are you sure that your unit dates from the mid-1970’s?
As it's marked T* (indicating multi-coating) it must date from 1978 at the very earliest
And it seems from the Europa data that T* coating was progressively introduced across the product line, with the 8x30's not multi-coated until 1983
Again consistent with this, my 1981 pamphlet designates the x40 and larger models as T*, but not the x30 and smaller models


John
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Old Wednesday 9th October 2019, 05:55   #17
Canip
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Thank you, John.
Memory is a tricky thing, but I am convinced I had the 8x30 before 1980. With a bit of luck, I may still find the purchase receipt. Let me go and dig.
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Old Thursday 10th October 2019, 19:06   #18
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Quote:
Originally Posted by John A Roberts View Post
So are you sure that your unit dates from the mid-1970’s?
As it's marked T* (indicating multi-coating) it must date from 1978 at the very earliest
And it seems from the Europa data that T* coating was progressively introduced across the product line, with the 8x30's not multi-coated until 1983
Again consistent with this, my 1981 pamphlet designates the x40 and larger models as T*, but not the x30 and smaller models
For what it's worth, Zeiss told me (based on serial number) that my 8x30B T* was manufactured in 1982. It is as shown in your photos here, diopter in front.
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