73 replies to this topic

[ihf]

Would you brag about it, or just modestly admit to your aw shucks little commercial scope? Hard to imagine, but there is a level at which they choose to not flaunt their toys.    Tom

You do tell the best campfire tales! Hard to believe, but wishing them to be true.

[TOMDEY]

You do tell the best campfire tales! Hard to believe, but wishing them to be true.

Here's my sketch of a client's remote vacation cabin from when I visited to service his little hobby SETI dish. I had been doing radio SIGINT for Uncle Sam, so was into that kinda stuff, and got called help out a high-roller. The Space Aliens did not take a shine to his snooping.    Tom

 

~for full resolution, click on~ >>>

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[edwincjones]

People forget how rare some of this equipment actually is. In 20+ years of this and going to many star parties, I'm not sure I've ever seen a Takahashi of any kind. Definitely never looked through one. I think I've see one Astro-Physics scope, a 6" I actually got to look through (no planets though, so it didn't leave much of an impression). I have gotten to look through huge dobs, thankfully.

 

I have used a 6" Tak, a 25 and 30" dob at NMSkies, seen and stood in line for a 36" dob at a star party,

used a 16" SCT and 22"? at StarHill Inn,  a 6" f22 once.

 These were wonderful to use, but not sure that  I would want one, pay for one, maintain one- it takes a lot of dedication!

 

My little stuff is so much easier to use.      edj

[PEterW]

I understand 120mm binoculars have been selling rather well... but these much bigger options make their presence felt more greatly.... Tom has relegated his to its own personal “doghouse”....

Peter

[salico]

they are a bit of effort - but really worth it! in my experience

[Gordon Rayner]

What might be a value , vs large double reversed reflector such as the example of this thread, of:

One large or medium aperture telescope, feeding the latest low light color video electronics ( vs. the green ITT 3rd Generation which I experienced at 1X in their binocular for a few nights at 6000 ft a few years ago)?

IIRC, video or other color electronic exposures of a few seconds or minutes, have been described . One can then view those exposures on a monitor, using both eyes simultaneously.


What method is used to parallelize a big reversed reflecting binocular? A comparator such as the JTII rhomboid or a semi-equivalent, or a binocular head, reversed, from a non-stereo microscope, or a reversed binoviewer?

Edited by Gordon Rayner, 23 October 2020 - 02:43 PM.

[PEterW]

Personally I’d be after a fast optical binocular with maximal exit pupil,for maximal rich field. Night vision is very nice for a range of objects, but sometimes you want the technicolour twinkles that you only get with glass. Different things to look at need different tools. I think I have cured any lingering aperture fever I may have once had

Peter

[Xilman]

Basing your decision wrt large bino's on advice from people who can't achieve stereopsis

is like asking a deaf man about HIFI.

Don't get me wrong. I am not advising anyone not to buy binoculars just because I can't use them properly. I was only recounting my experience. You must work out for yourself whether they work for you before investing serious money on a pair.

 

In fact, I use a pair of15x80s moderately often. I also have a pair of 25x150s stored in the garage. They are not in use because their equatorial mount didn't survive the last house move. They haven't been remounted because I ran out of round tuits.

 

Both pairs are being  / have been used to good effect --- one eye at a time.

 

Paul

[TOMDEY]

What might be a value , vs large double reversed reflector such as the example of this thread, of:
One large or medium aperture telescope, feeding the latest low light color video electronics ( vs. the green ITT 3rd Generation which I experienced at 1X in their binocular for a few nights at 6000 ft a few years ago)?
IIRC, video or other color electronic exposures of a few seconds or minutes, have been described . One can then view those exposures on a monitor, using both eyes simultaneously.
What method is used to parallelize a big reversed reflecting binocular? A comparator such as the JTII rhomboid or a semi-equivalent, or a binocular head, reversed, from a non-stereo microscope, or a reversed binoviewer?

I can describe that. The JMI RB's are unusually nice, in that both sides are entirely pre-collimated (aka optically aligned) unto themselves, and remain so, even as one executes the image-merging motorized tweakings. Most others ~cheat~ in vergence, by tip-tilting one (or both) Primary Mirrors, compromising their alignments, in the process. One could indeed use something like e.g. a giant collimator, optical flat bridge, etc. to verge the two sides... but interactively on the stars is actually good, even better. The betterness is because you also are dialing in your own personal prismatic differential, on the fly, to match how your eyes are behaving that night. So the view is, quite literally, hyper-comfortable... even more so than your plain uncorrected naked eyes. It's the complimentary opposite of eye strain >>> you actually feel more relaxed looking through the RB's than just walking around the observing field, looking up.    Tom

 

Images of a big (29-inch) collimator and a bridging ACF plano (30-inch) >>>

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[PEterW]

Long (unbalances) and umshielded interferometer path... eek! I don’t see any sensors for Elden corrections?
That Dahl collimator will be giving some people dobsonian aperture envy!!

Peter

[TOMDEY]

Long (unbalances) and umshielded interferometer path... eek! I don’t see any sensors for Elden corrections?
That Dahl collimator will be giving some people dobsonian aperture envy!!
Peter

Actually... we call that one the "little lab collimator" The big one is in vacuum and could swallow all of Hubble without even a hiccough! We of course absolutely characterize all test set wavefront mappings and back them out or measurements. Typical test residuals are down around λ/1000, no doubt less... but I don't like to brag.   Tom

 

DISCLAIMER: These claims are for novelty purposes only.    Tom

[Tyson M]

I have sent them an email (farpoint)

 

I might try to acquire the RB-10 before they are completely discontinued.  

[PEterW]

Lambda\1000....?! my friend has a noise floor around 10pm, on a good day when there aren’t too many people jumping around.
Got to be aware of systematic uncertainty terms... don’t want to making another “Hubble”?!

PEter

[Xilman]

Actually... we call that one the "little lab collimator" The big one is in vacuum and could swallow all of Hubble without even a hiccough! We of course absolutely characterize all test set wavefront mappings and back them out or measurements. Typical test residuals are down around λ/1000, no doubt less... but I don't like to brag.   Tom

 

DISCLAIMER: These claims are for novelty purposes only.    Tom

OK, I spotted the disclaimer but will analyze your statement anyway.

 

Assume it is a mirror designed to work in the optical at λ = 500nm (if it is a decametric radio reflector achieving cm smoothness is fairly easy), so λ/1000 is 0.5nm.  A quick rummage around in Wikipedia informs me that the Si-O bond length in silica is 0.16nm.  You are measuring your surface to an accuracy of about three atoms.

[PEterW]

0.16nm =160pm, as I said my colleagues have a noise floor of around 10pm. You can get surface roughness down in the nm range without a whole lot of trouble. Optical surfaces flat to lambda/100 or more are fairly common if you into making etalons.

Peter

Edited by PEterW, 27 October 2020 - 08:33 AM.

[TOMDEY]

Actually... we call that one the "little lab collimator" The big one is in vacuum and could swallow all of Hubble without even a hiccough! We of course absolutely characterize all test set wavefront mappings and back them out or measurements. Typical test residuals are down around λ/1000, no doubt less... but I don't like to brag.   Tom

DISCLAIMER: These claims are for novelty purposes only.    Tom

Lambda\1000....?! my friend has a noise floor around 10pm, on a good day when there aren’t too many people jumping around.
Got to be aware of systematic uncertainty terms... don’t want to making another “Hubble”?!
PEter

OK, I spotted the disclaimer but will analyze your statement anyway.

Assume it is a mirror designed to work in the optical at λ = 500nm (if it is a decametric radio reflector achieving cm smoothness is fairly easy), so λ/1000 is 0.5nm.  A quick rummage around in Wikipedia informs me that the Si-O bond length in silica is 0.16nm.  You are measuring your surface to an accuracy of about three atoms.

I knew this would get some scrutiny. The biggest challenge is that it's on large telescopes final certification, confirming that the operational wavefront across all fields shall/will meet requirements. That involves all sorts of test set and test config vs ops config differentials. The other ones are test set noise floor and any other systematic or random uncertainties. The unknown systematics are of greatest concern... what condemned Hubble to catastrophic anomalous failure (which event was subsequently repaired).

 

Bringing the noise floor precision (relative measurement noise) and accuracy (absolute vs ideal noise) down just involves ~best practices~ ... some heroic. Things like support of the (very large) Primary Mirror (1g vector vs 0g ops), system alignment differentials, vibration suppression/isolation, thermal control, vacuum environment, pupil distortion mapping (oft neglected by some shops) etc. etc. Under the best practices, it is possible to push the unknown systematics down below the residual random test noise. And that is where the (couple of thousandths) single pass wavefront RMS noise floor is achieved. The only way one can ironclad confirm that this has truly been achieved (vs simple brag 'n' boast) is when the system goes operational, and delivered product (imagery and on-board wavefront sensor suite)... confirm that it is indeed exceeding stringent requirements. At that point, what you see is what you got. If the system is one of many, one can (only then) use the history of success to credibly assert that the subsequent delivered product will indeed satisfy.

 

Optical metrology, in general, is Catch-22 difficult in that we use light to form the operational images ... and the same flavour of light for metrologies.

 

PS: My claim of λ/1000 test accuracy may be closer to λ/500. For large systems... the cost of testing alone can be a significant fraction of the entire build budget!  But in the context of "pay me now or pay me later" --- insurance that's well worth it!    Tom

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[PEterW]

To see what people’s best claim is for measuring the size of stuff round the world... https://www.bipm.org...keywords=Length

Peter

[ihf]

I had to read up on the Eastman Kodak mirror. Very interesting. Also here. Underbidding, conflict of interest, and lack of end to end testing. (Not to forget space cowboys that come to rescue the day.)

[TOMDEY]

I had to read up on the Eastman Kodak mirror. Very interesting. Also here. Underbidding, conflict of interest, and lack of end to end testing. (Not to forget space cowboys that come to rescue the day.)

Yep! Kodak vehemently recommended redundant testing of each mirror at the other's facility, but P&E would have absolutely nothing to do with that idea. Kodak also included a full-aperture Test of the entire telescope in autocollimation, including that in their proposal, when both companies were competing for the prime contract award. P&E said that was unnecessary and too expensive... they could save the cost of that by just being real careful. NASA chose the cheaper vendor (P&E) who proceeded to blow through the entire budget and far more... and deliver a fatally-flawed telescope. Note that a full system level test (that they deemed unnecessary) would have detected the flaw, allowing refiguring of the PM before it was sent up into outer space. When you add in the cost of the repair mission, the thing cost 10x + repair mission, over what was originally-budgeted.

 

"From its original total cost estimate of about US$400 million, the telescope cost about US$4.7 billion by the time of its launch."

 

One old saw regarding awarding custom-build contracts... "Don't go with the cheapest bid." That's just as true whether you're roofing your house or building a space telescope.

 

   Tom

[dustyc]

While one is waiting to get their binoscope built, read thru the book "The Hubble Wars". I had no idea there was a second mirror developed. Or that despite being hailed as a tech showcase, a lot of hardware was leftover 70's tech. Author Eric Chaisson does a great job weaving tech, personalities, and the detective work to get this craft in working order.

[TOMDEY]

While one is waiting to get their binoscope built, read thru the book "The Hubble Wars". I had no idea there was a second mirror developed. Or that despite being hailed as a tech showcase, a lot of hardware was leftover 70's tech. Author Eric Chaisson does a great job weaving tech, personalities, and the detective work to get this craft in working order.

Binoscopes are wonderful!

 

At ther risk of drifting off topic >>>

 

Yes! Eric gets most of the story right in his book there... extremely good read and revealing look into tight-knit ~Community~ that is big aerospace. Here's a peek inside >>> that ref is Chuck Spoelhof ~RIP~ who was one of my mentors, and recommended me for my Tech Fellow status, based on similar collaborations that we had shared, over the years. Chuck later sat on the Commission that investigated the Hubble Anomaly.    Tom

 

You can still find the book used on AbeBooks for a song and a few bucks... delivered to your door within a few days!

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[TOMDEY]

Binoscopes are wonderful!

 

PS: Last pic from the Chaisson book on the left and from a casual white paper that Malacara And I presented locally, a few years earlier. It was as if we somehow had seen into the future... feeling that something in production, somehow, somewhere --- was going terribly wrong. That eventually became history.    Tom

 

~click on~ >>>

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[ihf]

I assume NASAs project management competence slid with its budget in the 1970s. Fortunately we soon are going to get a prettier telescope with a way more complicated and folding mirror. Gold is best!

 

James Webb Optics

"JWST's primary mirror is a 6.5-meter-diameter gold-coated beryllium reflector with a collecting area of 25.4 m2. If it were built as a single large mirror, this would have been too large for existing launch vehicles at the time of design and construction, although new launch vehicles have now the ability to carry mirrors up to 9 meters without folding. The mirror is therefore composed of 18 hexagonal segments which will unfold after the telescope is launched. Image plane wavefront sensing through phase retrieval will be used to position the mirror segments in the correct location using very precise micro-motors. Subsequent to this initial configuration they will only need occasional updates every few days to retain optimal focus. This is unlike terrestrial telescopes, for example the Keck telescopes, which continually adjust their mirror segments using active optics to overcome the effects of gravitational and wind loading. The Webb telescope will use 126 small motors to occasionally adjust the optics as there is a lack of environmental disturbances of a telescope in space."

 

[TOMDEY]

I assume NASAs project management competence slid with its budget in the 1970s. Fortunately we soon are going to get a prettier telescope with a way more complicated and folding mirror. Gold is best!

 

James Webb Optics

"JWST's primary mirror is a 6.5-meter-diameter gold-coated beryllium reflector with a collecting area of 25.4 m2. If it were built as a single large mirror, this would have been too large for existing launch vehicles at the time of design and construction, although new launch vehicles have now the ability to carry mirrors up to 9 meters without folding. The mirror is therefore composed of 18 hexagonal segments which will unfold after the telescope is launched. Image plane wavefront sensing through phase retrieval will be used to position the mirror segments in the correct location using very precise micro-motors. Subsequent to this initial configuration they will only need occasional updates every few days to retain optimal focus. This is unlike terrestrial telescopes, for example the Keck telescopes, which continually adjust their mirror segments using active optics to overcome the effects of gravitational and wind loading. The Webb telescope will use 126 small motors to occasionally adjust the optics as there is a lack of environmental disturbances of a telescope in space."

I worked on the null lens for that and also coarse and fine alignment sensors... few patents. Indeed a very sophisticated observatory. Tom

 

~click on~ >>>

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