The Easy Way to Collimate a (Dobsonian) Telescope

[@markbergendahl2651]

Thanks for the clarification. Always something new to learn. I'm keeping the link to this video because it's very good !

[@SimRacingVeteran]

I just bought an 8” dobsonian. I plan on mostly having 2” eye pieces. My laser collimator is only 1 1/4 inches. Do I really need at 2” collimating laser?

[@NewMoonTelescopes]

The spider is a "curved vein" spider. It effectively "removes" diffraction spikes by spreading the diffraction out over the entire airy disc. Although you no longer see diffraction spikes, the diffraction is still there (in fact, quite a bit more so than with a straight vein spider-because the veins on curved vein spiders are typically thicker and longer, causing a slightly larger obstruction). We typically do not use them, but if a client requests one, we have no problem installing it. Thanks!!

[@davidclouthier3598]

I am a beginner with a 10-inch dob that I got brand new out of the box the other day and put together. all the collimation videos I have watched all tell something different. so how does a beginner know they have or are doing the correct thing.? now I see here you have to centre spot the secondary. if so, then why don't new telescopes come with that done for us? what about scope with no centre dot on the primary like a 130 solo-mark? now it gets difficult for a beginner, so what is the correct easy way? One says to tighten the screws on the secondary one says to loosen or tighten one then do the opposite with the other two screws one states to loosen the middle screw oh yeah and I nearly lost my secondary down the tube onto the primary.. so where is the easy method.. ? one video had me loosen off the primary mirror that the screw and spring went into tube. what is the home position of the mirrors as a starting point?

[@NewMoonTelescopes]

De-focusing to 4 or 5 rings gives you a larger image. If the image is in the center of your FOV, the rings should be circular in shape if properly collimated. If not, they will appear oval, or mis-shapen in some other way. The "star-test" is also a great way to judge (all be it somewhat subjectively) the quality of your optics.

[@jonathanhansen3709]

I would suggest when you receive your laser collimator you check it on machinist V-block. Any good machine shop will have one. Place the barrel of the collimator in the V of the block and turn it on. Project the laser dot against a wall at least 20 feet away and begin turning the barrel inside the V-block. There should be absolutely no deviation up or down or sideways in the laser dot. If it does, your barrel is either not perfectly cylindrical or your laser is not properly aligned in the collimator. Send it back.

[@NewMoonTelescopes]

Astute point.

[@kretieg2943]

Purchase a quality focuser such as a Moonlight or Starlight and you wont encounter that problem. I personally have a Moonlight with swing filter holder. I keep a variable polarizer permanently attached. Of greater concern is losing parallelism between the laser diode and the barrel of the collimator. Take care to keep the collimator in its case when not in use and not to toss that case around to much or you will be reparalising

[@MichaelBernardo]

Thanks for the video. That's a cool secondary spider. What do the diffraction spikes look like?

[@jrock357mag]

Great video, clear, concise, and to the point. Thank you!

[@markbergendahl2651]

The video would be better if we had seen close up views of where the laser was on the mirror. Also, if using a star to test collimation, how do you then adjust the bottom mirror accurately since you have to then move the telescope to access the mirror bolts and the star image used as a reference is gone?

[@bikEarth]

He day to use polaris star which will stand stil on your ocular. The only proble is that with a 16" maede is not confortBle to more from focuser to the botton

[@rodsmolter5046]

A more accurate way is to use the barlowed laser method or a cheshire collimator. That will get the primary mirror accurate enough that a star test won't be needed. You need really good seeing conditions for a star test to be of much use in my experience. Having a second set of hands helps makes it much quicker if using a cheshire. I have my wife turn the nobs while I'm at the focuser. I've since invested in a Glatter tublug laser collimator so I can do it all by myself in seconds from the back of my scope(16" dobsonian). Quick and extremely accurate tool, but quite expensive.

[@NewMoonTelescopes]

You would.. as long as your 2"/1.25" adapter is well machined (most are).

[@StargazerFS128]

Great video, I just purchased a 12" light bridge, used but in pristine condition, using a laser collimator I can easily hit the center of the primary then tweak the primary to hit center of target on collimator. Easy enough one would think but I notice 2 issues, first once I move the scope up from horizontal o notice the beam travels a tad off center of grid on collimator as though moving the scope up is causing primary to shift, yes locking screws are tight. Second, assuming I'm on target everywhere I notice that the beam doesn't strike the secondary in the center, should it be striking the secondary dead center? Could this mean the secondary is not itself centered to the tube? Thx!

[@NewMoonTelescopes]

First-the shift you are seeing when moving from horizon to zenith is likely truss flex. With a 6-tube truss this is relatively common, and unfortunately, not a whole lot can be done about it. Hopefully, it is just a couple mm or less Second, you just need to square your focuser up to your secondary. Since (I don't believe) there are set screw adjustments to tilt your focuser-leave your laser in the focuser, slightly loosen the 4 screws that hold it down, and take a few pieces of folded up paper (or super thin card board) and use them as shims to tilt the focuser until the laser is hitting the center of the secondary. Over compensate slightly, because when you tighten the four screws back up, it will likely move again. It's trial and error until you are centered. As long as your spider is tight, you probably will only need to make the adjustment once a year-if that. Good luck!

[@tomkrzyt]

In my case the beam didn't strike the center of the secondary mirror in the center but fortunately this point was on the major axis of ellipse. In that case the secondary mirror was simply too close to the primary mirror.

[@starrvalley12]

After collimating for your 2" eyepieces will you be collimated for 1.25" eyepieces?

[@Sharpless2]

yes. Changing eyepiece diameters should not at all affect collimation or focus.

[@ohwell2790]

What do you do to make sure the set screw does not move the collimator off center?

[@NewMoonTelescopes]

I typically use compression ring style adapters. But even with that, unless you set your eyepiece in the adapter the same exact position the collimator was in the adapter-you would have a slight variance. You could always use one of those centering adapters in lieu of either, however.

[@mrappe51]

Got volume all the way up and can barely hear it

[@SimRacingVeteran]

He’s a telescope guy eh, not a sound engineer.

[@MrWesleymoon]

Lol I tend to always turn the screw too much and takes me like 15 dam minutes to collimate my scope :-)

[@ianexcalibur7096]

Just collimate using a star...... can't get any more accurate than a star.

[@e.morrienh]

thank you for this video :)