What if...... (2 Viewers)

jan van daalen · Jan 18, 2020

henry link said:
Hi Jan,

Is the last drawing of the eyepiece correct, or was the middle lens reversed after the drawing was made?

Also, how are the prisms oriented in the photos? Is the eyepiece end of the prism assembly up or down? Which prism in the Retrovid has the roof edge in the last photo? Is it the one on the left or the right side of the prism assembly as it appears in the photo? I'm asking because the roof can be in either of the two prisms and the the light path can travel through the prisms in either direction. I'm not quite certain from the photos which of the four possible configurations is being used.

Thanks,

Henry

Hi Henry,

These are very good questions. Specially the first one:t:

The bin was already in pieces by the time we came (he had to make special tools to open it) so I don't know the answer on your second question also.
I'll call him monday.

It is possible that he reads this and mails me sooner.

Jan

denco@comcast.n · Jan 18, 2020

henry link said:
Whether a prism is undersized doesn't depend on it's actual size, but on whether it's entrance face is too small for the objective lens light cone when the light cone reaches the prism and that depends on the focal ratio of the objective lens and the distance between the lens and the prism. A bigger prism might be undersized if it's entrance is placed too close to the objective lens and a smaller one could be large enough if it's placed far enough back from the lens and/or the focal ratio of the objective is low enough to converge the light cone to a small enough diameter before it reaches the prism entrance.

In your current collection you have at least two binoculars with prisms that are so undersized that a straight prism edge impinges on the axial exit pupil. Those would be the Swarovski 8x30 Habicht and the Kowa BDII 10x42.

Over the years I've posted instructions for several ways to determine how much off axis vignetting is present in a particular binocular. You could try searching for one of those old posts if you want to experiment with the Retrovid.

Thanks, Henry. That explains a lot. Very interesting. Any ideas why the Retrovid prism would be larger? it sounds like it depends on the total optical design of the binocular. They changed the deisgn of the Retrovid and it probably needed a bigger prism. Did they change the focal ratio on the Retrovid compared to the old one?

henry link · Jan 18, 2020

[email protected] said:
Any ideas why the Retrovid prism would be larger?

Larger than what? In the photos the Retrovid prism is placed next to an SP prism of unknown size.

From just looking at the photos I'm not certain that the glass path through the Retrovid is longer than the other one or that its clear aperture is wider. The opening in the baffle at the top of the Retrovid prism housing looks smaller than the opening at the top of the other prism's housing. Is one turned upside down? Are they configured differently?

Too many unknowns to conclude anything.

NDhunter · Jan 19, 2020

Henry:
Good catch, as there is much less room in the slender tube of the new Trinovid, to mount a prism than most other binoculars. Any size comparison here is deceiving.

It seems many questions are unknown with Jan's photos. The lenses in which position, up or down and more.
This is unfortunate.

So, it is probably better to just wait for a better explanation of the optical design of the new Trinovid.

In the meantime, those that have used this binocular find it well done. That is what counts.

Jerry

jan van daalen · Jan 19, 2020

henry link said:
Larger than what? In the photos the Retrovid prism is placed next to an SP prism of unknown size.

From just looking at the photos I'm not certain that the glass path through the Retrovid is longer than the other one or that its clear aperture is wider. The opening in the baffle at the top of the Retrovid prism housing looks smaller than the opening at the top of the other prism's housing. Is one turned upside down? Are they configured differently?

Too many unknowns to conclude anything.

Good point. Next time I'll measure the sizes. The "standard" prism has the size of several SP prisms found in 42mm bins. It wasn't a small sized prism.

Jan

jan van daalen · Jan 19, 2020

henry link said:
Hi Jan,

Is the last drawing of the eyepiece correct, or was the middle lens reversed after the drawing was made?

Also, how are the prisms oriented in the photos? Is the eyepiece end of the prism assembly up or down? Which prism in the Retrovid has the roof edge in the last photo? Is it the one on the left or the right side of the prism assembly as it appears in the photo? I'm asking because the roof can be in either of the two prisms and the the light path can travel through the prisms in either direction. I'm not quite certain from the photos which of the four possible configurations is being used.

Thanks,

Henry

Hi Henry,

The last drawing of the eyepiece is the correct one.

The size of the "standard" prism can be found in almost all 42mm Far East produced bins. 32mm bins prisms are normally smaller. In this case the 35 Retrovid prism is bigger compared to the regular 42mm prisms bins.
So far for comparison.

If we call the roof part of the prism Pechan and the other one Schmidt it is obvious that the Schmidt prism side is much longer compared to the standard 42mm prism.

The light enters the prism from the objective side which is from the bottom on the photo. In the second photo the prism is just turned 90 degrees for comparison.

The yellowish colour is the genuine colour caused by the diëlectric coatings/phasecoating.

Jan

jan van daalen · Jan 19, 2020

henry link said:
Thanks, Jan. I think I've got it now. I've noticed that the "other" prism in the Schmidt-Pechan prism is sometimes referred to as a "Pechan" prism, but I think its correct names are Bauernfiend prism (for the inventor) or Semi Pentaprism or Half Pentaprism.

So, from the photos it appears that light travels through the Retrovid S-P prism in this order: objective lens > Semi Pentaprism (with roof) > Schmidt prism > eyepiece.

The "standard" S-P prism in the photos follows this order: objective lens > Schmidt prism (with roof) > Semi Pentaprism > eyepiece.

Henry

Hi Henry,

So the Retrovid follows the same "system" as the SF.

Jan

henry link · Jan 19, 2020

Jan,

I deleted my post, which was incorrect about where the roof is in the Retrovid prism. It can never be in the Semi Pentaprism. I'll post again with corrections later.

Henry

Rico70 · Jan 20, 2020

jan van daalen said:
The light enters the prism from the objective side which is from the bottom on the photo. In the second photo the prism is just turned 90 degrees for comparison.

The yellowish colour is the genuine colour caused by the diëlectric coatings/phasecoating.

Thanks Jan. Have you made any measurements regarding the function of phase coating?

Rico70 · Jan 20, 2020

[email protected] said:
Any ideas why the Retrovid prism would be larger?

In addition to what Henry has already said, the relative size of the prism basically depends on the size of the exit pupil (7x35 = 5mm) and on the visual field (or rather, on the apparent width of the observation window).
Then, there is also a component to reduce or avoid "vignetting" in the image that the eyepiece will see.
And in this case, but from the available photos it is not clear, there could also be a shape component of the prismatic system (width and length), since the format of the frame that housed the old prisms (UD), today finds itself having to accommodate prisms different (SP).

jan van daalen · Jan 20, 2020

Rico70 said:
Thanks Jan. Have you made any measurements regarding the function of phase coating?

Hi Rico,

It is my understanding that it is not possible to measure the function of the phase coating if you do not know the exact type of glass and the material used for the diëlectric coatings. We did run numerous tests in the past just to find out it is not possible. One can find out if it is there but in no way the quality of it.

Jan

Rico70 · Jan 20, 2020

jan van daalen said:
One can find out if it is there but in no way the quality of it.

Thanks, Jan. What you say is very interesting (at least for me) and at the same time a little disappointing. I was convinced that with a spectrograph and various polarized lights, it was possible to evaluate a "pseudo-quality" or at least a quantity of the transmission function...

jan van daalen said:
...it is not possible to measure the function of the phase coating if you do not know the exact type of glass and the material used for the diëlectric coatings.

I'm sorry for my curiosity, but when you know the type of glass and the diëlectric coatings (this is not needed for the "reflective face"?), how do you test?

jan van daalen · Jan 20, 2020

Rico70 said:
Thanks, Jan. What you say is very interesting (at least for me) and at the same time a little disappointing. I was convinced that with a spectrograph and various polarized lights, it was possible to evaluate a "pseudo-quality" or at least a quantity of the transmission function...

I'm sorry for my curiosity, but when you know the type of glass and the diëlectric coatings (this is not needed for the "reflective face"?), how do you test?

Hi Rico,

Go to www.verrekijkerforum.com (it is under construction

) and scroll all the way down to phase coatings, you'll understand.......hopefully.

Jan

Rico70 · Jan 20, 2020

jan van daalen said:
Go to www.verrekijkerforum.com (it is under construction) and scroll all the way down to phase coatings, you'll understand.......hopefully.

It seems to me quite understandable :t:
You did a great job, but you don't explain how you do the tests.

And the German part has to be translated separately.
This point is interesting here, but I think it refers to the complete binoculars and not to the direct measurement of the prismatic system (tell me if I'm wrong):
[...]laboratory tests show that the influence due to aberrations and manufacturing tolerances is significantly higher than that due to the quality differences in the phase coatings[...]

Another interesting point is that they imagine a test on the limit resolution ...

Too bad that only Swarovski replied and without giving accurate explanations. Maybe there is reserve on these crucial points?

Looking at the photos of the tests (are they photos?) I think the best is the Ultravid, with which you can see at the same time, the Moon, Saturn and Jupiter
http://www.verrekijkerforum.com/download/file.php?id=65

Thomas_M · Jan 20, 2020

henry link said:
Hi Jan,

OK, this time I'm pretty sure I've got it right.

Yes, the Retrovid follows the same arrangement as the SF and the "standard" prism.

The image of the Retrovid prism next to a diagram of a Schmidt-Pecan prism below shows light from the bottom traveling first through the Schmidt prism and then through the Semi-Pentaprism and then out the top. Note that the arrows in the diagram are reversed from the actual light flow. That doesn't matter since light can travel through the prism from either direction as we see in your cutaway photo of the SF and a Swaro SV, which has its prisms installed backwards from the SF.

Henry

Henry,

thanks a lot, but as far as I can see the shape of both prisms in the Retrovid is quite different from that in your drawing. Frankly, to me the prisms do not look like Schmidt Pechan. If you take into accont all images Jan has posted it seem to me that the light enters from the objetive lens to the left prism and exists from the roof prism. I would be interesting to have a look with the apperture in front of the eyepiede could be removed.

Thomas

jan van daalen · Jan 20, 2020

Rico70 said:
It seems to me quite understandable :t:
You did a great job, but you don't explain how you do the tests.

And the German part has to be translated separately.
This point is interesting here, but I think it refers to the complete binoculars and not to the direct measurement of the prismatic system (tell me if I'm wrong):
[...]laboratory tests show that the influence due to aberrations and manufacturing tolerances is significantly higher than that due to the quality differences in the phase coatings[...]

Another interesting point is that they imagine a test on the limit resolution ...

Too bad that only Swarovski replied and without giving accurate explanations. Maybe there is reserve on these crucial points?

Looking at the photos of the tests (are they photos?) I think the best is the Ultravid, with which you can see at the same time, the Moon, Saturn and Jupiter
http://www.verrekijkerforum.com/download/file.php?id=65

Rico,

If you would read it, you will read how it was done.
BTW, Swarovski did gave accurate explanations.
Read it again.

Jan

henry link · Jan 21, 2020

Thomas_M said:
Henry,

thanks a lot, but as far as I can see the shape of both prisms in the Retrovid is quite different from that in your drawing. Frankly, to me the prisms do not look like Schmidt Pechan. If you take into accont all images Jan has posted it seem to me that the light enters from the objetive lens to the left prism and exists from the roof prism. I would be interesting to have a look with the apperture in front of the eyepiede could be removed.

Thomas

Thomas,

Thanks for sending me back to the drawing board. Once again I had to delete a post with incorrect information. My latest mistake resulted from second guessing something I thought I knew, which is that the roof can be in either the Schmidt or the Bauernfiend prism in what we call a Schmidt-Pechan prism. When the roof is in the Schmidt prism the Bauernfeind prism requires mirror coating and when the roof is in the Bauernfeind prism the Schmidt requires mirror coating.

Almost all illustrations I found of S-P prisms show the roof in the Schmidt, but I finally found one with the roof in the Bauernfeind from a diagram of an old Swarovski 7x42 SLC. As you can see below it's a much better match for what we can see of the Retrovid prism in Jan's photo. It's in good agreement with your interpretation of the light from the objective entering the left prism (Schmidt, mirror coated with no roof) and exiting the right prism (Bauernfreind, roof with no mirror coating).

Jan's cutaway of the Swarovski EL SV below shows that the prism arrangement from the old SLC has been abandoned in favor of a Bauernfeind entrance prism (mirror coated with no roof) and a Schmidt exit prism (roof, no mirror coating).

Henry

henry link · Jan 21, 2020

Thought I would add these screen captures of quotes from "Opto-mechanical Systems Design" by Paul R Yoder jr.

The reference to "Seil, 1991" is to Konrad Seil's 1991 paper "Progress in Binocular Design", in which he describes the coating compromise inherent in the Schmidt-Pechan variants.

Thomas_M · Jan 21, 2020

henry link said:
Thomas,

Almost all illustrations I found of S-P prisms show the roof in the Schmidt, but I finally found one with the roof in the Bauernfeind from a diagram of an old Swarovski 7x42 SLC. As you can see below it's a much better match for what we can see of the Retrovid prism in Jan's photo. It's in good agreement with your interpretation of the light from the objective entering the left prism (Schmidt, mirror coated with no roof) and exiting the right prism (Bauernfreind, roof with no mirror coating).

Jan's cutaway of the Swarovski EL SV below shows that the prism arrangement from the old SLC has been abandoned in favor of a Bauernfeind entrance prism (mirror coated with no roof) and a Schmidt exit prism (roof, no mirror coating).

Henry

Henry,

thanks a lot, this looks very convincing!

I am learning, so far I thought, that a Schmidt Pechan prism is always characterized by a Schmidt prism with roof and a Bauernfeind prism without roof, but it seems that there are different variants which are all called Schmidt Pechan.

Then, I have a hard time to understand your comparison with the Swarowski glasses, it ist also not clear to me what is shown on the pictures with the cuts (Zeiss Victory SF right, Swaro EL SV left?)

I am confused, you are saying that the design of the retrovid resembles that of the old 7x42 SLC? To me it looks similar to that of the Zeiss Victory SF, although the Schmidt prism of the retovid is much wider.

Thomas

jan van daalen · Jan 21, 2020

Thomas_M said:
Henry,

thanks a lot, this looks very convincing!

I am learning, so far I thought, that a Schmidt Pechan prism is always characterized by a Schmidt prism with roof and a Bauernfeind prism without roof, but it seems that there are different variants which are all called Schmidt Pechan.

Then, I have a hard time to understand your comparison with the Swarowski glasses, it ist also not clear to me what is shown on the pictures with the cuts (Zeiss Victory SF right, Swaro EL SV left?)

I am confused, you are saying that the design of the retrovid resembles that of the old 7x42 SLC? To me it looks similar to that of the Zeiss Victory SF, although the Schmidt prism of the retovid is much wider.

Thomas

Hi Thomas,

Yes, the right one is the SF.
It is easy to see.
One objective lens less and the prism "upsidedown" causes a weight shift towards the eyepiece, resulting in a complete neutral balance. Something the original EL also had but the ELSV lacks.

Jan

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