OCAL Collimator - Forums

Topic starter

Mar 30, 2022

Has anyone tried the OCAL collimator on their RC scopes?

The general feedback on this collimator is good but RC scope are a bit special 🙄

The manufacturer has issued this video on how to use their collomator on RC scopes but I would rather prefer direct feedback from people here.

https://youtu.be/EB-tWVhEPTs

hughsie

Mar 30, 2022

I have a StellaLyra RC8 and have struggled with collimation for over a year. I have probably spent more on gadgets than the actual scope itself to assist me but have to say that the OCAL and the HoTech Laser Collimator have this winter really helped in getting my collimation where it is today.

On my RC8 there is a baffle extension that needs to be removed before using the OCAL. The circles you can create and cross hair really enable you to centre the secondary and align the primary. I have used it twice and with each iteration (or should I say as I become more fluent with the software) collimation has got better.

Whilst the OCAL will get you very close to collimation, a star test is by far the best method and if you really wanted to nail collimation down then this last step is a must.

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SemiPro

IOTD Staff

Mar 30, 2022 · Edited: Mar 30, 2022

I still find the best way is to just to use your average cheshire to rough it in mechanically, and then suffer under the stars for maybe an hour tops using the following method:

https://www.skydude.me/at8rccoll.html

In a nutshell, you adjust the primary to get a nice looking doughnut, and then the secondary is adjusted to get nice symmetrical corners. You might have to ping-pong back between the two as adjusting one can affect the other.

BONUS ROUND !!!!
Mirror spacing is kind of a huge deal for RC's. I have yet to try this, or even find a good way to do it on an RC8 but it is a factor:
https://www.cloudynights.com/topic/423163-precise-rc-mirror-spacing/?p=5461926

Edit: Looks like a decent way to use a ronchi eyepiece with an RC8 can be found here: https://www.cloudynights.com/topic/765474-tpo-rc8-correct-focal-length/

This is the best I have been able to do (so far) on an APS-C sized sensor, while keeping in mind there is a 0.8x refractor FR/FF attached to it: https://www.astrobin.com/7q69z2/

Engaging Supportive

hughsie

Mar 30, 2022

I still find the best way is to just to use your average cheshire to rough it in mechanically, and then suffer under the stars for maybe an hour tops using the following method:

https://www.skydude.me/at8rccoll.html

In a nutshell, you adjust the primary to get a nice looking doughnut, and then the secondary is adjusted to get nice symmetrical corners. You might have to ping-pong back between the two as adjusting one can affect the other.

BONUS ROUND !!!!
Mirror spacing is kind of a huge deal for RC's. I have yet to try this, or even find a good way to do it on an RC8 but it is a factor:
https://www.cloudynights.com/topic/423163-precise-rc-mirror-spacing/?p=5461926

Edit: Looks like a decent way to use a ronchi eyepiece with an RC8 can be found here: https://www.cloudynights.com/topic/765474-tpo-rc8-correct-focal-length/

This is the best I have been able to do (so far) on an APS-C sized sensor, while keeping in mind there is a 0.8x refractor FR/FF attached to it: https://www.astrobin.com/7q69z2/

I have never come across the sky dude link, if only I had a lot of pain would have been avoided. Many thanks for sharing that.

SemiPro

IOTD Staff

Mar 30, 2022

I still find the best way is to just to use your average cheshire to rough it in mechanically, and then suffer under the stars for maybe an hour tops using the following method:

https://www.skydude.me/at8rccoll.html

In a nutshell, you adjust the primary to get a nice looking doughnut, and then the secondary is adjusted to get nice symmetrical corners. You might have to ping-pong back between the two as adjusting one can affect the other.

BONUS ROUND !!!!
Mirror spacing is kind of a huge deal for RC's. I have yet to try this, or even find a good way to do it on an RC8 but it is a factor:
https://www.cloudynights.com/topic/423163-precise-rc-mirror-spacing/?p=5461926

Edit: Looks like a decent way to use a ronchi eyepiece with an RC8 can be found here: https://www.cloudynights.com/topic/765474-tpo-rc8-correct-focal-length/

This is the best I have been able to do (so far) on an APS-C sized sensor, while keeping in mind there is a 0.8x refractor FR/FF attached to it: https://www.astrobin.com/7q69z2/

I have never come across the sky dude link, if only I had a lot of pain would have been avoided. Many thanks for sharing that.

No problem! I think consumer RC's get a bad rep because people try to collimate them like a newtonian and things start getting out of hand. At the bottom of the page you can also find the link to variations of the same collimation method.

severinbb

Mar 30, 2022

I came across this: https://www.cloudynights.com/topic/757247-ai-based-wave-front-sensing-and-collimation/

It provides true analysis of your collimation, and has found that perfectly concentric circles are not necessarily perfect collimation (due to central obstruction centering).

I haven't tried this yet, but I want to

Gustav Lundby

Sep 28, 2025

I had good experience using OCAL 3. Here is my view after collimation of my RC8, without removing baffle tube. I have also the focuser tilt and a TS 2.5” rack and pinion focuser.

📷 capture_20250224115632217.jpg

Last evening star test:📷 HD_23463-RGB-session_1-cbg-csc-St.jpg

GregsAstrobin

Sep 30, 2025

If you have a 3D printer you can try the camera with concentric circles technique inexpensively with the DCAL, found here:

DCAL Camera Collimator for Reflecting Telescopes by Dave Aldrich | Download free STL model | Printables.com

The focus is fixed but the image is still plenty clear to do the job. I have used on a Newtonian, SCT and Hyperstar.

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