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Telescope Laser Collimator

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Neil Wyatt08/03/2018 20:55:14
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A long while ago Clive generously sent me a couple of little laser modules that were not as 'tight in the beam' as needed for their original purpose.

The spot is about 2mm at 2m which is fine for what I needed and I made this laser collimator some time ago:

collimator.jpg

I finished a bit more neatly, and I have recently upgraded it with a 3D printed housing for a 2032 lithium cell which runs the laser fine. The black bit at left has a screw on cap for changing the cell and the lower part of it was printed so a suitable switch and brass battery contacts could clip/glue in.

chapter 8 (8).jpg

The laser is mounted in a block mounted using an 0-ring and three set screws. The device is calibrated by rotating in in a v-block and adjusting the screws until the dot remains stationary on a suitably distant wall.

The telescope is set so the secondary mirror is eyeballed to be aligned with the eyepiece mount and main mirror (effectively the secondary fills the whole view and shows the whole of the main mirror, a simple cap with a central hole to replace an eyepiece makes this easy). The laser is fitted in the eyepiece holder and the secondary adjusted until the laser spot is in the dead centre of the main mirror. the main mirror is then adjusted so the reflected spot essentially goes back down the barrel of the laser! The centre lines of the eyepiece and both mirrors are then aligned.

Thanks Clive!

Neil

Clive Hartland08/03/2018 22:43:03
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Good one there Neil, I have a couple of tube type Lasers but only one PSU for them. one has a beam that will reach out about a half mile would make a good drain Laser. The smaller one has a lower power beam which is quite fine. This one was for projecting through a telescope in tunnels.They are both tube mounted.

Clive

not done it yet08/03/2018 23:13:42
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Posted by Clive Hartland on 08/03/2018 22:43:03:

... The smaller one has a lower power beam which is quite fine. This one was for projecting through a telescope in tunnels...

Lasers were used more than forty years ago to plot the path of drains and tunnels. Used for tunnelling for the abstraction pipes for filling Rutland Water, from the Welland and Nene, and were pretty well on aim, as they tunnelled from both ends and met in the middle.

Doubtless used a decade later for the Chunnel. A bit further, but a lot bigger hole, that one!

I would think they are now far more precise than back forty or fifty years ago ... and they were good enough back then!.

But the old theodilite, etc was very accurate a century before. Some guy went c.1500 miles on a circuitous route and finished up about 50-300 yards (can’t remember precisely how far he was out on his calculations) error when he got back to his origin. Annoyed at such a large error he later found that it was a nearby mountain that mucked up his measurements, by altering his vertical alignment by a change in the direction of the gravitational field, on part of his route. Luckily, lasers are not so affected by gravity!

john carruthers09/03/2018 08:25:43
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Very nice Neil.
I use 'keyring' red lasers for collimation. They fit in a 1.25" hoover tube with a few holes tapped round.
The green pointer in a 2" tube I reserve for the big refractors like Greenwich.
A mirror on the wall brings the spot back where you can see it and doubles the effective distance

Edited By john carruthers on 09/03/2018 08:26:15

Clive Hartland09/03/2018 08:28:04
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Tunnel borers are Laser guided plus Gyro theodolites to take a fix from the start position.

I did some work one time for a well known firm, they wanted a truly vertical aim line for a weapon. the best i could achieve with repeated readings on a sensor at 30 mtrs was 0.15 of a mm. Things change rapidly in the Surveying world and new techniques arrive almost weekly.

john carruthers11/03/2018 07:50:49
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Telescope collimation, a can of worms with various opinions.
Do you Barlow it Neil?

I find it is possible to get a single laser spot to return to the origin but take a circuitous route so still be slightly off.

I get it as close as I can then use a star as the final arbiter.

Neil Wyatt11/03/2018 20:49:16
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I think the trick part is getting the secondary in position first.

Alignment is easy enough, but the secondary can be 'aligned' optically but poorly placed.

All three of my newts are quite long f4.6 and f8 so not hugely fussy about collimation.

(Slightly embarrassed to realise I have three...)

john carruthers12/03/2018 07:59:33
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Only 3 !!?
cheeky

I just gave a 12" Newt/Cas Fullerscope and an 8" SCT to Monkton Observatory, still have a shed full to take with me to Wales.
I should thin them out a bit more, but it's like choosing which child to leave behind .

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