Easiest way to collimate your telescope primary mirror!

Last month, I gave my refractors a well-deserved break and brought out the trusty ONTC Newtonian Reflector.
Two common challenges with these types of telescopes are collimation and flat frame calibration. I’ve definitely struggled with both in the past, spending countless hours to achieve decent collimation. Even with practice, the results weren’t always repeatable. Tightening the laser collimator or camera can slightly tilt it in relation to the optical axis, meaning that while the laser might show perfect collimation, swapping it for the camera often reveals a misalignment.
My first thought was to use an OCAL, which threads onto the corrector. However, I found it a bit fiddly and not very intuitive, at least in my experience. I wanted a method where the camera could be in its imaging position, initial autofocus could be done, and then, lastly, collimation could be performed. After some research, I discovered this could be done using a Tri-Bahtinov mask by aligning each of the three diffraction patterns with the collimation bolts.
So, I decided to give it a shot and 3D-printed a Tri-Bahtinov mask with an additional top cover that exposes only one axis at a time, allowing precise adjustments of each primary mirror bolt. The results were incredible! I’ve never achieved such perfect star shapes with my ONTC before, and you can see the results in the photo below.
This led me to an additional idea: combining the collimation accessory with two other crucial tools for these types of telescopes- a dust cover and an aperture mask. The dust cover is self-explanatory, while the aperture mask helps reduce unwanted reflections from the internal parts of the telescope tube. These accessories are easily attached via magnets embedded in a compression ring at the edge of the telescope tube. For more details on this 5-in-1 Deep Sky Dad Cover Kit, you can check it out in our shop: shop.deepskyda...
Now, back to the Ghost Nebula image: This result is based on 15.5 hours of data (464x2-minute exposures) using the Skywatcher EQ6-R mount. In the past, this mount posed problems at long focal lengths, often resulting in elongated stars, even with guiding. To address this, we developed and refined a solution over the years by adding an encoder to the RA axis and our own mount circuit, which reads the RA axis's physical position. This allows for accurate tracking without the need for guiding, even at 1250mm focal length. As for dithering-yes, you can still do direct mount dithering (in SGPro or NINA) without autoguiding.
Lastly, after collecting all the data, proper flat frame calibration is crucial. We already offer flaps for telescopes up to 8" in our shop (shop.deepskyda..., and we’re currently working on a new design for 10" telescopes, along with a major update to our flaps lineup-stay tuned on our TH-cam channel! This image served as a proof-of-concept test, with calibration working flawlessly and eliminating those pesky dust motes.
Music from #Uppbeat (free for Creators!):
uppbeat.io/t/i...
License code: YUIHZSNBG3JSQHW4

[@lynnhilborn5947]

I ordered the kit for my 8” ONTC… one question- how do you know which bolt to adjust ? Perhaps a video showing the association of the mask and the open portion of the blocking cover and how that relates to a particular collimation bolt.
Looking forward to using it !

[@DeepSkyDad]

Of course, we can create a video or photo with an explanation 😊. But to explain in words: the mask has three distinct sections, each spaced 120 degrees apart. Each section is marked on the mask to indicate its direction. To align the mask with the bolts, simply position the mask (along with the compression ring) so that one of the three marks points toward one of the collimation bolts.

[@justklaas4703]

A "normal" Bahtinov mask is used to get good focus. The effect of out of focus, is that the intersection of the three lines is not in a single spot.
While collimating your main mirror, you also try to get the intersection of the three lines in the same spot. (times 3: one for each knob).
So how do you discriminate between out of collimation and just out of focus?

[@pavlini0]

You run autofocus prior to collimation and estimate best focus via FWHM. Thats how you know that asymmetrical axes are due to miscollimation. In my experience this method works well.

[@Jacq_Deepsky-Villa-Karimunjawa]

Amazing !

[@miketronix]

I am thinking of ordering your nice kit for my ontc8
A bit silly question regarding the aperture mask, does it do the similar work like the mask that I’ve already 3d printed and placed on the primary mirror that helps avoiding the clipping issue on the stars? Or I’ll have to keep that one?

[@DeepSkyDad]

@@miketronix it has similar purpose. The difference is that mask on primary hides clips, while aperture mask hides obstacles or reflective surface on the inside of the tube (e.g. nuts used to attach guide scope shoe to the top of the tube)

[@AaronDalton1]

Do you have any more info about the encoders on the eq6r you talked about?

[@DeepSkyDad]

@@AaronDalton1 will release separate video, we are currently preparing new controller circut box :)

[@indysbike3014]

Can you use this method on a 8" RASA?

[@DeepSkyDad]

I think so, with appropriate central hole for mirror adjustment 😊 if you would be willing to try it on your RASA, drop us an email to [e-mail]

[@n5sdm]

If that is the "easy way"....... I will stick with my laser and flashlight

[@DeepSkyDad]

@@n5sdm if it works for you, by all means 😄