Autocollimator question about resolving power

[Ethan Scott]

Thanks for the detailed information.

 

[eKretz]

I'll second that again too. I have definitely gained a bit more insight into the instruments, so thanks to all who replied.

I managed to pick up another interesting instrument a little while ago for pretty much no money. A theodolite - or more accurately a total station. It is a Swiss-made Wild Heerbrugg T3000 surplused from Lockheed Martin. Been having some fun playing with that. This particular instrument reads to 0.1 arc-second - standard deviation is claimed to be 0.5 arc-second. Just playing around with it I placed it at a set distance from my television and measured pixel pitch. Looked up the spec online and my TV has a pixel pitch of 58.7 pixels per inch, or almost exactly 0.017" pixel pitch. I took several angular measurements from the center of a red pixel to the center of the next red pixel and averaged. After calculating, damned if that thing didn't nail it right on the dot. Farthest from average was something like 0.0002" or thereabouts. Pretty neat.

Got the idea to get one to play with from a guy on YouTube that checked the accuracy of his dividing head with one. Figured I couldn't go wrong even just using it as a telescope for the kids for the price. The optics are very sharp and about 60x at infinity focus.

 

[cameraman]

I'll second that again too. I have definitely gained a bit more insight into the instruments, so thanks to all who replied.

I managed to pick up another interesting instrument a little while ago for pretty much no money. A theodolite - or more accurately a total station. It is a Swiss-made Wild Heerbrugg T3000 surplused from Lockheed Martin. Been having some fun playing with that. This particular instrument reads to 0.1 arc-second - standard deviation is claimed to be 0.5 arc-second. Just playing around with it I placed it at a set distance from my television and measured pixel pitch. Looked up the spec online and my TV has a pixel pitch of 58.7 pixels per inch, or almost exactly 0.017" pixel pitch. I took several angular measurements from the center of a red pixel to the center of the next red pixel and averaged. After calculating, damned if that thing didn't nail it right on the dot. Farthest from average was something like 0.0002" or thereabouts. Pretty neat.

Got the idea to get one to play with from a guy on YouTube that checked the accuracy of his dividing head with one. Figured I couldn't go wrong even just using it as a telescope for the kids for the price. The optics are very sharp and about 60x at infinity focus.

I saw that video too... lol

I have the cameras that bolt onto his instrument - "Metric" ultra precise surveying cameras built by Wild Heerburg.

We / my little group are essentially building high end digital versions of such cameras / arrays for specific applications and things we need to roll out. (Much more modern + additional capabilities; best of old school and "New" school ).

On the SW and Hardware side Leica Geosystems would be one of our direct competitors.

We have the capability to record and "Render" anything from the size of a bug to a mountain (optically)/ three dimensionally (very cleanly , nothing lost). [Mainly for high end VR applications and "Other".].

T3000 very nice instrument.

Some Total stations / theodolites also can have autocollimators built into the main telescope also.

That's cool about pixel pitch.

For high precision angle measuring theodolites if you find a "Subtense bar*" (sp) you can measure distances with pretty extreme accuracy (in terms of field precision) also (angle measurements and Z distance) in some cases much more accurate than reflectorless EDM (Electronic distance measurement) and comparable with corner cube prism based measurement on a total station.

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* Subtense bar is usually a one or two meter long bar with targets on each end mounted on another tripod and sometimes optically plumed to a point on the ground / survey nail or marker. These bars sometimes have some sort of thermal compensation to maintain constant length (like integrated invar wires etc.) Even if the subtense bar is not perfectly aligned perpendicular to the theodolite very accurate Z (distance measurements) can be made.

_______

** Was interesting to see the dividing head accuracy and repeatability and statistics there of... :-)

 

[eKretz]

Yeah that's the one. He has a few other good videos. Your project sounds pretty interesting. I read about the subtense bar usage in the T3000 manual, pretty neat - Wild also offered an autocollimator attachment, but finding one would probably not be easy. Mine has the optional higher magnification eyepiece and a built-in autocollimation target for aligning with another theodolite, but no autocollimation attachment.

My T3000 is spitting out some errors intermittently, so I am about to get out the o'scope and start working through test points. Got a lucky grab of the service manual after searching for weeks.

 

[eKretz]

Whoo-hoo! Licked the error problem in the Wild. It had a flat (really dead, measured 0.0VDC) lithium battery soldered on one of the circuit boards. Ordered a new one, desoldered the dead one and soldered the new one on. Still a few lingering errors so I decided to try a "cold reset" key combo I found in the service manual. After re-entering some factory calibrated constants (sticker had them inside the battery compartment) and recalibrating a few other things, et voila, good as new and thank you Lockheed Martin for the cool piece of gear.

 

[eKretz]

resolving power think 1/100" ruler or scale. you reach a point where markings so thin hard to see or read.
.
some optical instruments have a 10 arc second crosshair. how I know 1 arc second is .006" wide at 100feet so 10 arc second is .006" wide at 10 feet. just looking at a 1/100" ruler at 10 feet you can measure width of crosshair
.
focused at infinity you dont talk about .001" only arc seconds

Dragged the Wild out to fiddle around with it tonight, reading back in this thread I saw Tom's test for crosshair width in arc seconds. Looks like this Wild has a cross hair width of maybe 2-3 arc seconds or so - that is a hundredths scale viewed through the eyepiece at almost exactly 10 feet.

 

[Orbital77]

Yes, was thinking about picking one up if I get a chance at one cheap for playing around with, possibly surface plate checking. And those kinds of links are exactly what I was looking for, thank you cameraman.

I would suggest a cheap ( < $500 ) Davidson Optronix dual axis. Send it to Davidson for a service, might need cleaning and gluing back the splitter - their most common issue. It is an excellent product , can focus very close and has a large aperture - can use small targets in low light. You can make your own mirrors and right angles.

Sorry if this was already discussed - haven't read the whole thread.

 

[Dresden]

I recall the single crosshair is 5 Arc seconds, the paired crosshairs are 15 Arc seconds at the gap

 

[eKretz]

Looking at that scale at 10' I would say that the single lines aren't 5 arc-second, unless Tom's numbers are off. Is that dependent on the fitted eyepiece? Mine has the optional high magnification eyepiece fitted, I was thinking if the target was magnified and the lines are the same size, they would effectively cover less angle.

 

[thermite]

I would suggest a cheap ( < $500 ) Davidson Optronix dual axis. Send it to Davidson for a service, might need cleaning and gluing back the splitter - their most common issue. It is an excellent product , can focus very close and has a large aperture - can use small targets in low light. You can make your own mirrors and right angles.

Sorry if this was already discussed - haven't read the whole thread.

Happy to see it. Wasn't aware of that problem.

I have three of the Davidson D-600's holding down storage racks. Round Tuits to fab new light sources are on backorder, as usual.

I did get one wedge and two of the - WTH are they? Parallel differential? mirrors as well.

 

[Orbital77]

Happy to see it. Wasn't aware of that problem.

I have three of the Davidson D-600's holding down storage racks. Round Tuits to fab new light sources are on backorder, as usual.

I did get one wedge and two of the - WTH are they? Parallel differential? mirrors as well.

I don't know the 600 - I think that's a kind of comparator and way to accurate for my needs. I have the large aperture one, the 656. I ( used to ) need the low light capability. Usually splitters are comming apart and and ( I suppose ) there may be some fungus problem. All fixable. Under serious correction but I think yours in full kit could split 0.2 microns in a meter. Needless to say, you breathe reading is gone.

 

[Conrad Hoffman]

FWIW, we use much coarser instruments at work, arcminutes rather than arcseconds. They are extremely sensitive, so when you get to instruments at the sub arcsecond level, expect to need perfection in mounting, temperature control and who knows what else. At that level think in terms of everything being made out of rubber.

 

[eKretz]

Yep, no question about that. Finding a stable platform is not easy, and better hope there's no heavy traffic nearby, wind etc. Even setting on 3 points on my basement floor there is some flutter on my instrument's position displays when it's set for its finest resolution. The finest it can resolve is .00001 degree, when set in decimal degrees mode. In DMS it's 0.1 arc-second, which is about 3 times coarser. Resolution ≠ accuracy, of course.

And I just tried a quick test on the reticle crosshair width by aligning the top edge of the crosshair with a distant target edge, then the bottom. The differential is showing on the display as almost exactly 3 arc-seconds for the crosshair width.

 

[thermite]

I don't know the 600 - I think that's a kind of comparator and way to accurate for my needs. I have the large aperture one, the 656. I ( used to ) need the low light capability. Usually splitters are comming apart and and ( I suppose ) there may be some fungus problem. All fixable. Under serious correction but I think yours in full kit could split 0.2 microns in a meter. Needless to say, you breathe reading is gone.

Agree. Planned mount is just under 1200 lbs Avoir of Herman Grade A granite SP @ 68 F +/- 2 F or so.

Slab under is only about 5", but the subgrade compaction nearly 40 years ago was world-class, the PO & builder being VP of a road paving firm.

And almost as anal about such things as me late Dad was about building runways for B-36 bombers!

 

[CarbideBob]

.... The finest it can resolve is .00001 degree, when set in decimal degrees mode. .

Just to think about that number in resolving power is wow.
Unless I mucked up this is a 5 inch target fifty miles away for your tank gun or laser gun ignoring all the other things.
This here old school stuff. No lasers, no high tech just plain optics.
Bob

 

[thermite]

Just to think about that number in resolving power is wow.
Bob

Look how tiny his instrument is, as well.

"Naval rifle" AKA "main battery" heavy-gun "directors" on War Two battleships had optical range finders (pre and with RADAR).

Some were on a SIXTY FOOT baseline!

To me, the REAL marvel of what he has is ....that it "ain't"!

 

[eKretz]

Just to think about that number in resolving power is wow.
Unless I mucked up this is a 5 inch target fifty miles away for your tank gun or laser gun ignoring all the other things.
This here old school stuff. No lasers, no high tech just plain optics.
Bob

Even more wow, by my calculation that's 0.553" at 50 miles.

 

[thermite]

Even more wow, by my calculation that's 0.553" at 50 miles.

Only in a vacuum. Main reason Hubble & c. can do so much better than ground-based giants many times their size.

Even an ordinary K&E transit, we had distortion off thermals and turbulence in the atmosphere at but a hundred yards or several - depending on weather, humidity, and time of day.

 

[CarbideBob]

Even more wow, by my calculation that's 0.553" at 50 miles.

That's what I typed in first and then I thought that impossible so recalculated and oops.
Too many zeros, too old of eyes.
To think how old this tech is and what it can do....

 

[eKretz]

Only in a vacuum. Main reason Hubble & c. can do so much better than ground-based giants many times their size.

Even an ordinary K&E transit, we had distortion off thermals and turbulence in the atmosphere at but a hundred yards or several - depending on weather, humidity, and time of day.

Yes, those are theoretical numbers, of course. When the target is wiggling all around it's hard to get any kind of repeatable location dialed in. Some days it's minimal and some it's awful. Same goes for viewing stars and planets through a telescope. Sometimes they are crystal clear, others, a blurry mess.