TheSkySearchers

I've been wondering, what kind of tools there are for collimating a 300 mm F/4 scope?
I'm especially interested in getting the secondary right. I also read somewhere that a collimation cap is not good enough for fast scopes, and they are, actually, hard to find these days. And most people don't have empty film canisters around the house any more either. I wonder if the young people have even seen them.

I think the barlowed laser is good enough for the primary, but getting the secondary in the right place is quite hard.

The only tools for secondary placement I've heard of this far are CatsEye Telecat/TeleTube XL(S), but haven't found out how they actually work.

Another problem, when it comes to making the tools, is, that most of the Europe is metric, and it's a bit hard to find, say, 1.25" or 2" plastic tubes. You can find some inch-sized (usually 3/4", 1", 1.5" and 2") water pipes with 3 mm wall thickness, though...

Collimation cap, Cheshire eyepiece, standard laser, Howie Glatter holographic collimator are the usual tools.

cheshire and a laser, you can do a good job with either but i believe an exelent job with both'

i use a cheshire or even a collimation cap could work to alighn the secondary to the focuser then follow through the rest with a laser collimater.

a defocused star collimation for the final tune .

I use the Howie Glatter laser and collimator on my 203 f5 Newt. Seems to work pretty good. But the Glatter collimator is not cheap. I bought it a couple of years ago and a member of my club derided me saying my laser would not work with it. Lo and behold - I found out the laser I bought was specifically for use with the collimator. Made my life ever so much easier - that and Bob's Knobs for the secondary mirror.

I was going to recommend the Howie Glatter laser collimator with Tublug ("collimator") as it's called, but after seeing the prices online, find something else. I got my collimator from Howie himself at the RTMC. The next day I realized the Tublug was missing and paid another bunch for that, basically a piece of plastic with a lens. I was in a spending mood because I had just won the ES ED127CF triplet in a free door prize lottery but I think the prices have gone up drastically after his death, more than justifiable.

TuBlug seems to be just a barlowed laser. At least according to this page:
https://www.collimator.com/collimation

turboscrew wrote: ↑Sat Oct 10, 2020 11:58 am TuBlug seems to be just a barlowed laser. At least according to this page:
https://www.collimator.com/collimation

The Tublug is the plastic holder, it does not include the laser. It is sold in two parts. But yes the lens makes the combination a Barlowed laser.

I see the combined value of the parts listed online as a ridiculous $465, come on! I think I paid about $200 for the sum of both, can't quite recall how much. It is a really solid nice tool to have but there are less expensive alternatives that work, too.

SkyHiker wrote: ↑Sat Oct 10, 2020 3:18 pm

turboscrew wrote: ↑Sat Oct 10, 2020 11:58 am TuBlug seems to be just a barlowed laser. At least according to this page:
https://www.collimator.com/collimation

The Tublug is the plastic holder, it does not include the laser. It is sold in two parts. But yes the lens makes the combination a Barlowed laser.

I see the combined value of the parts listed online as a ridiculous $465, come on! I think I paid about $200 for the sum of both, can't quite recall how much. It is a really solid nice tool to have but there are less expensive alternatives that work, too.

I have this
https://www.astroshop.eu/laser-pointers ... 2-/p,59523
and this
https://www.astroshop.eu/barlow-lenses/ ... 5-/p,47674
and I took a bottom of an old vitamin container that fits on the focuser tube inside the telescope and made a small hole for the laser beam. That's my reflection screen. Somewhat cheaper...

turboscrew wrote: ↑Sat Oct 10, 2020 3:29 pm

SkyHiker wrote: ↑Sat Oct 10, 2020 3:18 pm

turboscrew wrote: ↑Sat Oct 10, 2020 11:58 am TuBlug seems to be just a barlowed laser. At least according to this page:
https://www.collimator.com/collimation

The Tublug is the plastic holder, it does not include the laser. It is sold in two parts. But yes the lens makes the combination a Barlowed laser.

I see the combined value of the parts listed online as a ridiculous $465, come on! I think I paid about $200 for the sum of both, can't quite recall how much. It is a really solid nice tool to have but there are less expensive alternatives that work, too.

I have this
https://www.astroshop.eu/laser-pointers ... 2-/p,59523
and this
https://www.astroshop.eu/barlow-lenses/ ... 5-/p,47674
and I took a bottom of an old vitamin container with a small hole that fits on the focuser tube inside the telescope. That's my reflection screen. Somewhat cheaper...

Yes that should work just fine so long as you (a) collimate the laser and (b) are able to get a good fit of the laser and adapter in the 2" focuser tube. The latter is what the Howie Glatter does really well. You can find out by rotating the combo around in the focuser and see if the dot stays in the same place, if not, adjust with tape or whatever works. My first laser was a Seben that looks like yours, for about $21. After collimating the laser, it worked fine.

SkyHiker wrote: ↑Sat Oct 10, 2020 3:36 pm

turboscrew wrote: ↑Sat Oct 10, 2020 3:29 pm

SkyHiker wrote: ↑Sat Oct 10, 2020 3:18 pm
The Tublug is the plastic holder, it does not include the laser. It is sold in two parts. But yes the lens makes the combination a Barlowed laser.

I see the combined value of the parts listed online as a ridiculous $465, come on! I think I paid about $200 for the sum of both, can't quite recall how much. It is a really solid nice tool to have but there are less expensive alternatives that work, too.

I have this
https://www.astroshop.eu/laser-pointers ... 2-/p,59523
and this
https://www.astroshop.eu/barlow-lenses/ ... 5-/p,47674
and I took a bottom of an old vitamin container with a small hole that fits on the focuser tube inside the telescope. That's my reflection screen. Somewhat cheaper...

Yes that should work just fine so long as you (a) collimate the laser and (b) are able to get a good fit of the laser and adapter in the 2" focuser tube. The latter is what the Howie Glatter does really well. You can find out by rotating the combo around in the focuser and see if the dot stays in the same place, if not, adjust with tape or whatever works. My first laser was a Seben that looks like yours, for about $21. After collimating the laser, it worked fine.

I already checked by rotating and the dot doesn't move anywhere - at least enough for me to detect.
And I tried with loosening the screws - I can move the laser, and the lit patch moves around, but the shadow of the doughnut still stays put.

Yeah, I know I did not pay that much for the Tublug - or the laser. Like I said - I've use the laser for nigh on 10 years now, and I'm pretty sure I bought the Tublug at the same time... but it sat dormant because of said astronomy club member, until I realized (about a year ago) that the laser was for the Tublug. There is NO WAY I would pay $465 for the two of them. No way. I think Howie must be rolling over in his grave seeing that pricing.

The way it is done in Obsession telescopes is by using a stencil with a hole on the offset position of your secondary mirror and place a dot on the mirror, examples and the formulas as well as tables for calculating the position is given in David Kriege's book "The Dobsonian Telescope". During manufacture a white dot is placed on the inside of the top section of the telescope. Using the 2" red laser provided you would first lineup your focuser, it has four adjusment screws, with the white dot before installing your secondary mirror, you then lineup the secondary mirror by placing the laser on the dot you have made on your secondary mirror. After this has been done collimation is easy because the scope has 3 knobs on the primary and 3 on the secondary. You get the laser in the centre of your primary mirror with the knobs on the secondary then use the knobs on the primary to get the return beam of the laser to hit the laser face in its centre. I have placed a white ring around the laser's hole and painted the inside black, so I basically tune the 3 primary knobs for minimum reflected laser light from the laser's face. This procedure insures near perfect collimation and I believe the impressive views you get from a Obsession is not just because of the excellent and big optics but also because you can easily get its collimation perfect.

Piet Le Roux wrote: ↑Sun Oct 11, 2020 6:50 am The way it is done in Obsession telescopes is by using a stencil with a hole on the offset position of your secondary mirror and place a dot on the mirror, examples and the formulas as well as tables for calculating the position is given in David Kriege's book "The Dobsonian Telescope". During manufacture a white dot is placed on the inside of the top section of the telescope. Using the 2" red laser provided you would first lineup your focuser, it has four adjusment screws, with the white dot before installing your secondary mirror,

I drilled a 1.5 mm hole in the opposite of the middle point of the focuser hole (using some baking paper), and covered it with a piece of white electric isolation tape. When you put a laser into the focuser, you can see a glowing red point from the outside.

you then lineup the secondary mirror by placing the laser on the dot you have made on your secondary mirror.

How do you make it, and how do you remove it?

After this has been done collimation is easy because the scope has 3 knobs on the primary and 3 on the secondary. You get the laser in the centre of your primary mirror with the knobs on the secondary then use the knobs on the primary to get the return beam of the laser to hit the laser face in its centre. I have placed a white ring around the laser's hole and painted the inside black, so I basically tune the 3 primary knobs for minimum reflected laser light from the laser's face. This procedure insures near perfect collimation and I believe the impressive views you get from a Obsession is not just because of the excellent and big optics but also because you can easily get its collimation perfect.

For primary mirror, I use barlowed laser.

Here is a pdf copy of the book:
https://www.pdfdrive.com/the-dobsonian- ... 91419.html
You dot your secondary permanently, I used a very fine permanent marker. I cannot seem to understand the advantage of the barlowed laser ajusting the three primary mirror adjusters for minimum reflected light from the face of the laser collimator works best for me.
Here is my 2" laser:

Piet Le Roux wrote: ↑Sun Oct 11, 2020 7:29 pm Here is a pdf copy of the book:
https://www.pdfdrive.com/the-dobsonian- ... 91419.html
You dot your secondary permanently, I used a very fine permanent marker. I cannot seem to understand the advantage of the barlowed laser ajusting the three primary mirror adjusters for minimum reflected light from the face of the laser collimator works best for me.
Here is my 2" laser:

The barlowed laser is supposed to be more accurate. It's quite easy too, Instead of directing the beam back where it came from, tha laser is used to illuminate the doughnut, and the doughnut shadow is directed around the hole where the beam came from - in the middle of the end of the focuser draw tube.
The laser doesn't need to be well collimated.

Piet Le Roux wrote: ↑Sun Oct 11, 2020 7:29 pm Here is a pdf copy of the book:
https://www.pdfdrive.com/the-dobsonian- ... 91419.html
You dot your secondary permanently, I used a very fine permanent marker. I cannot seem to understand the advantage of the barlowed laser ajusting the three primary mirror adjusters for minimum reflected light from the face of the laser collimator works best for me.
Here is my 2" laser:

Thanks. That book seems to contain this and that interesting stuff.

I use the Tectron tool set: For secondary: Sight tube, Cheshire, then Astrosystems 2" laser to hit the primary center spot, followed by the Barlowed Astrosystems 2" laser to collimate the primary. Final check of the entire system with a Tectron autocollimator.

Nowadays I do preliminary primary collimation with a laser (if I need to), and Barlow it for collimation.
Then I finish with Cheshire. I also use laser for squaring the focuser and aligning the secondary mirror.

Don't overthink it. When using a laser, make sure that it is well collimated and that it does not flop around in the focuser for the primary adjustment. Turn it around in the focuser to make sure of that. Once the primary is done, collimate the secondary. If the primary is good don't worry about extra accuracy by a Barlowed laser. Once the secondary is good any further adjustment only serves to distribute the light across the image, it will not further sharpen what you see. Put your eyeball approximately where the focal plane would be with the focuser empty, and center the secondary with whatever screws you need. Then do it all over again. The last secondary adjustment I mentioned is a one time thing. You don't need to do complicated math based on offsets, mark the secondary, or drill holes in your tube.

Recommended tools from extensive testing:
Combination sight tube + Cheshire tool: Astrosystems Light Pipe.
Sight tube: Astrosystems Light Pipe or Catseye Teletube
Cheshire Only: Farpoint, Catseye Black Cat
Laser: Farpoint, Howie Glatter
Barlowed laser: Astrosystems laser, Howie Glatter Tublug, Howie Glatter Barlow attachment
Autocollimator:
--single pupil: Farpoint, Catseye Infinity
--dual pupil: Catseye Infinity XLKP

For the 3 processes of collmation:
1) centering the secondary under the focuser: sight tube or the Combination tool
2) aligning the focuser axis by adjusting secondary rotation and tilt: Sight tube and or laser
3) aligning the primary's optical axis: Cheshire, Combination tool, Barlowed laser
4* for fast scopes and coma corrector users) eliminating residual errors: autocollimator