Zeiss New Product Development and How SF Binoculars Were Created (1 Viewer)

[Gijs van Ginkel]

Konrad Seil published an excellent SPIE paper in 1991 about the do's and don'ts with regard to prism coatings, that may shine some light on this discussion (Seil was the optical engineer for the Swarovski EL and the Zeiss SF).
Gijs van Ginkel

 

[John A Roberts]

Konrad's Seil's 12 page article from 1991 is entitled 'Progress in Optical Design'
It includes:
- discussion of lens coatings, along with prism designs and phase correction coatings, and also
- images and discussion of prism mounting in Swarovski Traditional ('Habicht'), SL and SLC models

The article can be be found here on the University of Arizona's website: https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/10/Seil-1991.pdf

The link directly opens the 2 MB PDF

John

 

[eronald]

Konrad Seil published an excellent SPIE paper in 1991 about the do's and don'ts with regard to prism coatings, that may shine some light on this discussion (Seil was the optical engineer for the Swarovski EL and the Zeiss SF).
Gijs van Ginkel

Thank you for the very interesting pointer, below is a link to the PDF for other interested individuals.

https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/10/Seil-1991.pdf

My idiot's reading of this says that porro prisms should be fairly generic, and also that one could expect substantial brightness improvement in an old instrument by using porros coated at the entry and exit faces, and made of glass with good transmission. The lenses would be left untouched. Also my intuition says high-transmitting glass for porros might be cheap because glass rejected for roof prisms might serve well.

I suspect that people who repair out of warranty binoculars as a trade know what they are doing better than the rest of us, and are already set up to do disassembly, cleaning, reassembly, collimation and releathering in a cost-effective way, and that if there were a real demand for updating instruments, they would also find a way.

Edmund

PS.
From reading the paper, the issues involved in roof prisms appear much more complex.

 

[Troubador]

Many thanks to both John and Edmund for providing the link to Konnie Seil's paper.

Lee

 

[jring]

My idiot's reading of this says that porro prisms should be fairly generic, and also that one could expect substantial brightness improvement in an old instrument by using porros coated at the entry and exit faces, and made of glass with good transmission. The lenses would be left untouched. Also my intuition says high-transmitting glass for porros might be cheap because glass rejected for roof prisms might serve well.

Hi,

coating just the surfaces of porro prisms is not going to improve things so much - after all it's just 4 surfaces (or even two if the prisms are cemented).

Objective is also 4 surfaces in the case of the usual fraunhofer or air spaced doublets (and 2 again for cemented doublet).

The largest gains will in the eyepiece as they usually have 3 or more groups and with 2 surfaces per group huge gains can be had for coating these.

Joachim

 

[eronald]

Hi,

coating just the surfaces of porro prisms is not going to improve things so much - after all it's just 4 surfaces (or even two if the prisms are cemented).

Objective is also 4 surfaces in the case of the usual fraunhofer or air spaced doublets (and 2 again for cemented doublet).

The largest gains will in the eyepiece as they usually have 3 or more groups and with 2 surfaces per group huge gains can be had for coating these.

Joachim

Joachim,

You are totally right. But to do a group you still have to disassemble it and also deal with the cemented doublets somehow. If the lenses are coated you need to decoat them, probably. Or maybe not. Someone has pointed out that single coatings are an acceptable first layer for multi-coating.

I was thinking of the Porro prism as a drop-in swap, and of transmittivity as much as of the surfaces, a glass change together with a coating change might make a really perceptible difference to the view. Think absoption spectrum.

In the case of old roof prism binos the dielectric coatings on the prisms makes a huge difference in sharpness with just that change as the paper points out, while in some designs there is an astonishing number of reflections. Maybe one can buy/remake these parts and drop them into old roofs

At some point I guess someone with access to an optics small-run manufacturing or prototyping lab will chime in and tell us what optical parts modern machines can custom make, when it comes to lenses, prisms, and coatings.

Living in France, I have learnt that there is usually some trick to get 80% of the results at 20% of the effort I suspect that the procedure you suggest is the most rational, for a hobbyist disassembling and cleaning oculars and possibly recoating a couple of lenses there maybe is the most effective time investment, the simplest, and the least risky as it wouldn't interfere with the collimation of the rest of the system.

At least we're having a fun discussion

Edmund

PS. The interesting takeaway from this discussion is that phase-coated prisms define the turning point at which roof-prism designs can truly compete with porros for sharpness.

 

[Patudo]

I don't think re-coating old lenses is realistic for the reasons already mentioned. A simple solution would be to have a good PRC optical company make/redesign new multi-coated lenses and prisms as replacement sets. There must be thousands of old Dialyts and Trinovids out there - the question is are there hundreds of owners willing to upgrade their old binoculars with new glass (and would hundreds be enough?). The glass used in top end PRC binoculars eg. the former Zen Ray and Vortex Razor seems pretty good. Holger Merlitz and others have also noted that porro prism binoculars require less strict tolerances than roofs, and if so replacement lenses and prisms (which would not require phase-coating) for the great classic porros would be less costly. Top tier PRC glass, in binoculars of the mechanical quality of an old Trinovid or Oberkochen, could make for a seriously nice package. I just don't know whether there is the business case for it - probably not, as presumably someone would have tried it if so?

 

[eronald]

I found this pdf by accident, it talks about transmission losses eg. in prisms. Dont know if it is really useful. I suspect some really old binos have substantial losses through absorption in the prisms, and not only surface-transition losses in the lenses.

https://www.schott.com/d/advanced_o..._tie-35_transmittance_of_optical_glass_us.pdf

Edmund