Meopta S2 Mysteries (1 Viewer)

I had a look at the Meopta website and their 2018 Sports Optics catalogue this morning. I left with a few questions, particularly about the S2 spotting scope.

The cutaway of the S2 angled version on page 38 of the catalogue shows a prism configuration quite unreadable to me. I've puzzled over it before, but a new description in the 2018 catalogue has this cryptic description: "A special system of 3 Porro prisms also provides the option of occasional astronomical observation". That statement suggests that perhaps the prism is an odd variant of a Porro Type 2 in which two of the three prisms are rotated in such a way that a 45º deviation results. That would be unique among spotting scopes, but if true it would have the advantage of not requiring mirror coatings compared to a Porro Semi-Pentaprism arrangement or phase correction compared to a Schmidt roof prism.

I also noticed that the objective lens in the website specs is described as 7 elements in 5 groups. I can't find all those elements in the cutaway. It looks like 4 or at most 5 in 3 groups unless maybe the prism is included as 3 elements in 2 groups.

Finally I noticed that Meopta has been using a superior multicoating they call Meolux on certain rifle scopes for several years, but for some reason has yet to introduce it on the binoculars or the S2 spotting scope, which still use the less transmissive Meobright. Why would they not use their best coating on their flagship products?

Anybody know anything about any of this? Maybe Lee could ask his contact at Meopta for some Enlightenment.

Henry

Hi Henry,
Why would astronomical observations benefit more from this system?
It seems an odd statement.

Any spotting scope can be used for astro observations, how is this different?

Some very high quality lenses use coatings that are not seen in the usual consumer lenses.
It may be that the rifle scopes are considered military optics and more highly specified.

Binastro said:

Why would astronomical observations benefit more from this system?
It seems an odd statement.

Click to expand...

I think they merely mean that the angled version is more suitable for astronomical observations.

The cutaway drawing of the S2 (and also that of the B1 binocular) falls under the category of "artist's impression". It would be interesting if the marketing people could provide us with more information but sometimes one has to question their understanding, or at least ability to communicate the details.

The graphic showing Meolux, Meobright and standard multi-layer coating also begs a few questions. To what instrument does it apply? What is the difference between these coatings and how many layers do they have? Are they tailored to the refractive indices of the specific elements and are there even coatings on the internal surfaces of cemented groups, as I believe is the case with Pentax XW eyepieces?

It would be a major achievement, Lee, if you could motivate some of the technical people from the optics manufacturers to participate on this forum!

John

Binastro said:

Why would astronomical observations benefit more from this system?

Click to expand...

Hi,

why an image erecting system consisting only of porro prisms (and thus no roof prisms) would be preferable for astronomy seems fairly easy to see:

- only total internal reflection - thus no need for silvering or aluminizing with the corresponding loss of light.

- no roof edge - no need for phase coating.

- no roof edge - no chance of an imperfect roof edge being visible.

But I have not found a way to combine 3 porro prisms to erect the image and offer a 45 deg eyepiece angle.

Joachim

jring said:

But I have not found a way to combine 3 porro prisms to erect the image and offer a 45 deg eyepiece angle.

Joachim

Click to expand...

Joachim,

I couldn't figure out how this could be done either, but today I cobbled together the components of a Porro prism in a way that does erect the image and offer a 45º eyepiece angle. I used four diagonal prisms in series, but I think Meopta accomplishes the same thing more elegantly with two diagonal prisms and what we might call a "half Porro". I think that's where the "3 Porro prisms" comes from, but it should read "a Porro prism divided into 3 parts" as is usually done with type II Porros. The rotatioal twists seen in the photo below between the first and second and third and forth diagonals is what allows this configuration to divert the exit beam by 45º while maintaining the normal image erection of a Porro.

If you look at the prism in the cutaway of the S2 on page 38 of the 2018 Meopta catalogue I believe you can see a diagonal prism is the first to receive the light from the objective. It diverts the beam 90º to the right into the "half Porro", which is rotated on the axis of the beam to divert it down, backwards and back again to the left into a second diagonal prism (invisible in the cutaway) which is also rotated on the axis of the beam so that the beam exits at a 45º angle from the entrance.

To me this looks like a very good way to make an angled scope. I'm surprised it hasn't been used by others.

John,

The instrument appears to be an unspecified rifle scope. Somewhere there is a mention that Meolux has 99.8% transmission and Meobright 99.7%, but of course with no mention of wavelength or refractive index. That would make Meolux about equal to the current offerings from other Alpha brands and Meobright a little behind.

From the graph I would expect about a 2% improvement over Meobright at 550nm, around 3% at 650nm and the most difference in the blue, around 4-5% at 440nm for complex binoculars or spotting scopes. The biggest visible difference would probably be more natural color.

Henry

Nice experiment Henry.
Gijs van Ginkel

Hi Henry,

very nice - that's most probably it!
And indeed, if all this is done with prisms and thus total internal reflection, it is preferable to anything containing roof prisms.

Joachim

Tringa45 said:

It would be a major achievement, Lee, if you could motivate some of the technical people from the optics manufacturers to participate on this forum!

John

Click to expand...

Working on it.

Lee

Just thought I would add a little more to my experience with simulating an angled Porro prism of the type that appears to be used in the S2. Just as you might expect rotating the entrance and exit diagonal prisms can accommodate any eyepiece angle from 0º to 90º. Each prism just needs to be rotated exactly half the desired eyepiece angle (in opposite directions) in order to keep the erect image from tilting. A 45º angle requires each to be rotated 22.5º, etc.

This system along with Nikon's oversized Schmidt seem like they should be everybody's first choices for angled scopes.

Henry,
Is that how fully variable eyepiece angle spotting scopes work?

Orion Grandview vari-angle 20-60x80 spotting scope for instance.
Or the one sold by Ace Optics.

Hi Binastro,

I wondered about that too. I suppose it's possible, but it's hard to visualize how it would work. The entrance prism would have to remain fixed and the exit prism would have to rotate along with the eyepiece, so the third prism would somehow have to rotate in a way that allows exactly half the total eyepiece angle to come from each.

Henry

I suppose it could have 2 to 1 gearing.
As the eyepiece is pulled down a prism could rotate.
A cheap broken vari angle spotting scope could provide the answer.

Our side piston lift has 2 to 1 action and has worked for decades.

@Henry Link, Among the top models, we have the Nikon ED82 (https://www.birdforum.net/showthread.php?p=3865770) & Kowa 883 (https://www.birdforum.net/showthread.php?t=125302) covered. Any chance of getting a review from you on the Meopta S2 82mm?

Cheers,
Kumar