Why couldn't a catadioptric or newtonian optical system be used in binoculars? (2 Viewers)

[WJC]

. The Yukon 30×50 binocular is a folded refractor.

It sure is. However, do you think the people who wrote the ad knew that . . . or cared? Did the importer knew or care?

It's like the photo of the 120x120 bino I've posted. People will brag about their new acquisition, show every neighbor who will look, and remain oblivious to the fact they aren't seeing an image magnified 120 times. That's all right, they were just in love with the big numbers printed on the backplates, anyway.

At the expense of being picked on for being arrogant (comma) again, I just have to say, "It's a wonder some people aren't too stupid to breathe on their own!

Aah, I feel better already. Now, if you will excuse me, I have to go repent. |:x|

Bill

 

[WJC]

This . . . . . . is London. Oops, wrong intro.

I see a lot of talk about f/1 mirrors, f/1.5 mirrors, and the like, and I would like to interject a few small chunks of reality.

I don’t care who you are, unless you have the budget of the federal government backing you up, your chances of getting it into an instrument that works well is about .001%. I have encountered a number of people, in my last 40 years in telescope making, who have gone weak in the knees over some f/1 mirror acquisition they made from Edmund Scientific, Surplus Shed, eBay, and the like and had big plans as to what they were going to make with it. However, I have yet to see any one of these projects come to fruition! I’ve grown Jaded; don’t give me hopes, dreams, and plans; show me products . . . with photos of a star field.

“Regardless how elegant the plan, from time to time you need to look at the RESULTS.”—Winston Churchill

Furthermore, I have never heard the starry-eyed discuss the secondary. An f/1 mirror is going to take a secondary of about 70% obstruction! Oops! There went the contrast you wanted. According to Rayleigh, you can’t achieve a diffraction limited system with it having more than an 18% obstruction. When planning a system, you have to plan the WHOLE THING! Elements and aberrations don’t live in a vacuum.

And, if you’re making the mirror:

* Small f/10 mirrors may be left spherical.
* f/9 mirrors produce very subtle shadows. Making them is not for the faint of heart or patience.
* f/7-f/8 mirrors can be made by anyone with patience and common sense.
* f/6 mirrors are beginning to get tough.
* f/4-f/5 mirrors separate the men from the boys.
* Below f/4, problems increase exponentially with EACH new f/ratio.
* F/1? God is still trying to finish his first!

Cheers,

Bill

 

[etudiant]

Why a central obstruction?
The mirror can be tilted so the secondary is out of the primary aperture.
Admittedly, this makes for a slightly more complex optical train, but when we're talking F:1 gear, surely a triviality.
FWIW, Perkin Elmer once had an open house fund raiser selling PE one of a kinds for a local school. One of the items in the sale was a little spotter, about 50mm aperture, that looked to be using an F:1 mirror. It went for about $1000 on a silent auction and I doubt the buyer had a clue what he had.

 

[WJC]

Why a central obstruction?
The mirror can be tilted so the secondary is out of the primary aperture.
Admittedly, this makes for a slightly more complex optical train, but when we're talking F:1 gear, surely a triviality.
FWIW, Perkin Elmer once had an open house fund raiser selling PE one of a kinds for a local school. One of the items in the sale was a little spotter, about 50mm aperture, that looked to be using an F:1 mirror. It went for about $1000 on a silent auction and I doubt the buyer had a clue what he had.

Etudiant:

It's pretty obvious that you're an intelligent person. So, I must ask: are you playing head games with me?

On this forum, we see folks wanting to get more from every optical system than most of them could ever provide. Do you suppose that when you TILT that system the aberrations stay the same? And correcting those aberrations would require additional elements--$$$, some of which would have to be TILTED, themselves.

Zeiss produced the first prismatic binocular in 1894 (121 years ago). In those years, there have been some brilliant people working to better the design. I am always glad when that happens. But, most of the new and wonderful (perceived) things that people have come up with have been gimmicks to take advantage of consumers: Zooms, Rudy coatings, Zip Focusers, click-stop focusers, electronic focusers, screw-up eyecups, built-in cameras, etc.

I don't want anyone to ever think I expect my word to be the last on any issue. But, I just want to give the quiet lurker something to think about. There's just too many people who like to walk the tracks without their hearing aids. :eek!:

 

[ceasar]

. The Yukon 30×50 binocular is a folded refractor. I have it and like it a lot, it has really excellent resolution but the transmission is low because of rather poor coatings. It is a bit heavy. The objective is probably a bit longer focal ratio than normal with binoculars.
Later they made a 20×50, but I don't have this.

They also do spotting scopes in 50 mm, 60 mm and 100 mm aperture that are also folded refractors.

As to the craziness of life, it was cheaper to send a letter from Scandinavia to England then back to Scandinavia, than it was to send it internally in Scandinavia. Also the postal language was French, but nobody in the main post office spoke French or understood it.

I'm not sure if investing in Iceland is a good idea. Our local Council lost £35 million doing exactly this, and we are still suffering the consequences. They are overpaid councillors who are not capable of running a corner shop let alone a council.

A British optical specialist completed half of a 12 inch Maksutov binocular, possibly the main mirror was F/1, I cannot remember. Unfortunately he did not live long enough to complete the instrument. I saw the half that he had made.

The Ampliivid 6×24 is a very nice and usable binocular which fits in your pocket. It has a wide field of view that is fully usable although the edge performance is not that good. The transmission is low so the images are a bit dull. It is a pity they don't make it nowadays with modern coatings.

Allbinos has an interesting article on the Amplivid with some pictures.

http://www.allbinos.com/166.1-article-Legendary_binoculars_-_Leitz_Amplivid_6x24.html

Bob

 

[etudiant]

Etudiant:

I must ask: are you playing head games with me?

Absolutely not, way too much respect.
But I do think that design suggestions such as the one for this thread are far enough gone that a little 'ad absurdum' is appropriate.

That said, there are telescopes that use the tilted mirror approach, google 'schiefspiegler' for lots of pictures and even a fine summary of making one.
http://www.clearskyobserver.com/index.php/20-telescopemaking/21-4-schiefspiegler

A binocular version could probably be made, for those with very plump wallets. Maybe not very handy, but all mirrors, so no CA apart from the eyepiece contribution.

Separately, while the Amplivid was light and with great FoV, it had minimal eye relief, so using it was not fun.

 

[[email protected]]

Allbinos has an interesting article on the Amplivid with some pictures.

http://www.allbinos.com/166.1-article-Legendary_binoculars_-_Leitz_Amplivid_6x24.html

Bob

They always fetch a good price on Ebay. Here is a nice one for sale.

http://www.ebay.com/itm/Leica-Leitz...Foto_Camcorder_Ferngläser&hash=item418f7cda9a

 

[[email protected]]

This . . . . . . is London. Oops, wrong intro.

I see a lot of talk about f/1 mirrors, f/1.5 mirrors, and the like, and I would like to interject a few small chunks of reality.

I don’t care who you are, unless you have the budget of the federal government backing you up, your chances of getting it into an instrument that works well is about .001%. I have encountered a number of people, in my last 40 years in telescope making, who have gone weak in the knees over some f/1 mirror acquisition they made from Edmund Scientific, Surplus Shed, eBay, and the like and had big plans as to what they were going to make with it. However, I have yet to see any one of these projects come to fruition! I’ve grown Jaded; don’t give me hopes, dreams, and plans; show me products . . . with photos of a star field.

“Regardless how elegant the plan, from time to time you need to look at the RESULTS.”—Winston Churchill

Furthermore, I have never heard the starry-eyed discuss the secondary. An f/1 mirror is going to take a secondary of about 70% obstruction! Oops! There went the contrast you wanted. According to Rayleigh, you can’t achieve a diffraction limited system with it having more than an 18% obstruction. When planning a system, you have to plan the WHOLE THING! Elements and aberrations don’t live in a vacuum.

And, if you’re making the mirror:

* Small f/10 mirrors may be left spherical.
* f/9 mirrors produce very subtle shadows. Making them is not for the faint of heart or patience.
* f/7-f/8 mirrors can be made by anyone with patience and common sense.
* f/6 mirrors are beginning to get tough.
* f/4-f/5 mirrors separate the men from the boys.
* Below f/4, problems increase exponentially with EACH new f/ratio.
* F/1? God is still trying to finish his first!

Cheers,

Bill

It is logical that the extremes in mirrors f/ratio would be very difficult to make. I have never really thought about it.

 

[Binastro]

. There are very large telescopes with very fast primary mirrors. Such as 8 m or 300 inch F/1. Others of F/1.25.
And designs for a 30 m telescope with an F/0.5 primary. Correctors are used.
The primaries are usually spherical.
The common low-priced Schmidt Cassegrains use F/2 mirrors.
there is nothing very difficult about making fast mirrors if the design requires it.

I also had a very strange Philips mirror system which seems to have perhaps an F/1 primary and you looked at it from the side. I never did find out what it was.

I have a Sigma 500 mm F/4 mirror lens, which is complex. It only works at one focusing distance. If you focus away from this point the image becomes progressively worse. I do not know how fast the primary mirror is on this.
There is also the Nikon 500 mm F/5 and I think the Zeiss 500 mm F/4.5. Again I don't know how fast the primaries are.
As has been said above the secondary obstructions are large and the contrast low.
The Minolta 250 mm F/5 .6 lens is very small and quite useful, but again the contrast is not very good.

 

[[email protected]]

. There are very large telescopes with very fast primary mirrors. Such as 8 m or 300 inch F/1. Others of F/1.25.
And designs for a 30 m telescope with an F/0.5 primary. Correctors are used.
The primaries are usually spherical.
The common low-priced Schmidt Cassegrains use F/2 mirrors.
there is nothing very difficult about making fast mirrors if the design requires it.

I also had a very strange Philips mirror system which seems to have perhaps an F/1 primary and you looked at it from the side. I never did find out what it was.

I have a Sigma 500 mm F/4 mirror lens, which is complex. It only works at one focusing distance. If you focus away from this point the image becomes progressively worse. I do not know how fast the primary mirror is on this.
There is also the Nikon 500 mm F/5 and I think the Zeiss 500 mm F/4.5. Again I don't know how fast the primaries are.
As has been said above the secondary obstructions are large and the contrast low.
The Minolta 250 mm F/5 .6 lens is very small and quite useful, but again the contrast is not very good.

How many telescopes do you have and are they all reflectors?

 

[WJC]

Absolutely not, way too much respect.
But I do think that design suggestions such as the one for this thread are far enough gone that a little 'ad absurdum' is appropriate.

That said, there are telescopes that use the tilted mirror approach, google 'schiefspiegler' for lots of pictures and even a fine summary of making one.
http://www.clearskyobserver.com/index.php/20-telescopemaking/21-4-schiefspiegler

A binocular version could probably be made, for those with very plump wallets. Maybe not very handy, but all mirrors, so no CA apart from the eyepiece contribution.

Separately, while the Amplivid was light and with great FoV, it had minimal eye relief, so using it was not fun.

Etudiant et al

First, thank you Etudiant; you’re very kind.

I support your interest in unobstructed systems, and need not look at any internet sites to see what CAN be done. Also, I was corresponding with Jose Sasian before he got his PhD in optics, have been a friend of Dick Buchroeder from the 80s and the late John Gregory since the 70s. Further, you may note ATM Journal had off-axis systems sprinkled throughout, and that the SECOND article in my first issue of ATMJ was on off-axis systems.

Binastro: you said, “There is nothing very difficult about making fast mirrors if the design requires it.”

That was spoken like a fellow who had read a lot, but who had never really made one. I mean no offence, whatsoever, but I think you should make, say, a good f/2 system and then report back to us. I have made over a dozen mirrors, from 6 to 12.5 inches in aperture, and I would as soon kiss an Eastern Diamondback on the lips as start such a project. The same would have been true 30 years ago.

All: It would seem that when the REALITY of a MASSIVE central obstruction for a fast mirror was revealed, who hadn’t considered that little contrast robbing reality, shifted to off-axis—pie in the sky—talk.

Folks, we’re talking about HAND HELD binos; what is there to be gained? Then, perhaps you could share the magnitude of improvement over conventional wisdom that will make all the additional work, testing, and other considerations worthwhile.

During a boat ride to Catalina, I had a conversation with Alan Hale, co-founder and then CEO of Celestron, (Oops, there I go name dropping, again. I dare not say he’s a friend, lest I really tweak the A-types) about why the cost of the C-5 was nearing that of the C-8. The reason:

“The C-5 is much harder to make than the C-8 … it’s because of the size.”

I thoroughly agree that conversations such as this one should be ALWAYS going on; it’s how we have advances in the art. However, it is only the thoughts that slip through the net of reason that will improve the art. I believe, further, optical and business realities should be liberally sprinkled, throughout such conversation.

I once had a 16-inch SCT (f/.5 primary). That would put all the rays of the visible spectrum into a miniscule portion of the Airy Disc (at the edge of the field). It was waterproof and only weighed 3 pounds. I was VERY proud of it. Then, the alarm went off and I had to take a shower and get to work. :t:

Cheers,

Bill

 

[etudiant]

. There are very large telescopes with very fast primary mirrors. Such as 8 m or 300 inch F/1. Others of F/1.25.
And designs for a 30 m telescope with an F/0.5 primary. Correctors are used.
The primaries are usually spherical.

Those big light buckets have to be fast, else the secondary sticks out into the stratosphere. Even so, just putting up their surrounding dome is an engineering challenge, especially as they are usually sited far from any industrial base.
I might add that pretty much all of the 8 meter plus telescopes now use active optics, many even on the primary, which does improve their performance, but at a considerable cost.

Seen that the binocular community is too conservative even to embrace Image Stabilization, despite its obvious huge benefit, it seems silly to be floating alternative optical schemes that offer little except added expense.
I will now retreat to my foxhole.

 

[WJC]

"it seems silly to be floating alternative optical schemes that offer little except added expense."

Bing . . . . O!

Bill

 

[[email protected]]

Those big light buckets have to be fast, else the secondary sticks out into the stratosphere. Even so, just putting up their surrounding dome is an engineering challenge, especially as they are usually sited far from any industrial base.
I might add that pretty much all of the 8 meter plus telescopes now use active optics, many even on the primary, which does improve their performance, but at a considerable cost.

Seen that the binocular community is too conservative even to embrace Image Stabilization, despite its obvious huge benefit, it seems silly to be floating alternative optical schemes that offer little except added expense.
I will now retreat to my foxhole.

What do you mean by active optics?

 

[etudiant]

What do you mean by active optics?

The mirror surface(s) are continually adjusted, primarily to offset atmospheric distortion but also to optimize the figure. A reference star is created with a laser that creates a fluorescing point about 50 miles up, which allows the distortions to be measured and corrected for. The Japanese Subaru telescope in Hawaii has an active secondary which is said to give especially good results. The active optics concept is the key to making larger telescopes, because the distortions brought about by the mirror's own weight limit single mirror sizes.
The James Webb telescope that is expected to succeed the Hubble uses active optics, partially also because the mirror is folded into a small package to launch, so when it unfolds it needs to unfold exactly so much, no more.

 

[[email protected]]

The mirror surface(s) are continually adjusted, primarily to offset atmospheric distortion but also to optimize the figure. A reference star is created with a laser that creates a fluorescing point about 50 miles up, which allows the distortions to be measured and corrected for. The Japanese Subaru telescope in Hawaii has an active secondary which is said to give especially good results. The active optics concept is the key to making larger telescopes, because the distortions brought about by the mirror's own weight limit single mirror sizes.
The James Webb telescope that is expected to succeed the Hubble uses active optics, partially also because the mirror is folded into a small package to launch, so when it unfolds it needs to unfold exactly so much, no more.

Interesting. There is a lot of technology there. I can't imagine the technicalities of getting a multi-mirrored telescope aligned.

 

[etudiant]

Interesting. There is a lot of technology there. I can't imagine the technicalities of getting a multi-mirrored telescope aligned.

A great site for optics in astronomy is by the European Southern Observatory.

http://www.eso.org/public/

They have superb videos that delve into the design of their telescopes and lots of good links.
The Keck twin telescopes in Hawaii, which are the first ground based large segmented mirror telescopes offer another superb site.

http://www.keckobservatory.org/

One can really get into the technology involved.
These giant scopes are the cathedrals of our day.

 

[bkrownd]

These giant scopes are the cathedrals of our day.

3 I sure wish we had the artwork and tranquility to go along with that image. I think it's more like an old top of the line sailing ship going on a voyage of discovery - a high tech prestige peice, government investment, military spinoffs, everyone thinks it's cool, long periods of isolation, low pay, uncertain future, lots of time breaking ice off the masts, etc

 

[etudiant]

3 I sure wish we had the artwork and tranquility to go along with that image. I think it's more like an old top of the line sailing ship going on a voyage of discovery - a high tech prestige peice, government investment, military spinoffs, everyone thinks it's cool, long periods of isolation, low pay, uncertain future, lots of time breaking ice off the masts, etc

All you say is also true, the pay is modest, the sites are isolated (although being isolated in Hawaii is not totally intolerable), the government has control, with the military a very interested observer, plus the work can be endless routine and the future is iffy, especially for an astronomy post doc.

Yet these observatories are todays cathedrals. Even though they don't have the art or the music of their predecessors, they have the same social motivation, to help us find where we fit in.

 

[OPTIC_NUT]

Here is a major problem with using very high powered binoculars
in a terrestrial application: atmospheric distortions of the
rays and the image are much stronger looking horizontally than vertically?
Add the common haze issue of the lower atmosphere and...what's the point.

Other issues with a reflector include contrast, of course. The effect of the
diffraction around the supports and secondary reflector. You can actually
get past this a bit with image processing, but it costs in resolution in the end.
Haze, most of the time, actually erases the difference between refractor and
folded reflector. Horizontally-used, that is. Not a problem if you look
between mountaintops, but that's a pretty rarified bird watching world, outside
of wildlife specials in Alaska or Iceland or following goats on the Matterhorn.

Anyway, the great long-ground-distance photos I see from reflector fans aren't any different
from the ones from refractor fans. Over a mile, they are both smoky, so the point is moot.

But...a small Cat, short distance? There is a grey level to it. I adapted a chunky
500mm telephoto to an eyepiece. It's got great power, esp. with the little barlow swapped in.
But taking pictures, I always have to down-sample and re-negotiate saturation and contrast.
Obstruction noise happens but, hey....for the price, no CA to see. It's all about trade-offs.