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Ocal Electronic Collimator SCT Opinion

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#1 Vinnyvent84

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Posted 12 February 2024 - 09:41 AM

Good morning everyone,

 

Reaching out to see if anyone has any experience regarding the Ocal Electronic Collimator 3.0 Pro (or earlier versions)? I tend to struggle with collimation and I live in an area with generally poor seeing on average in combination with a very small sky horizon in my yard. This gives me a small window of time for my viewing at night and I waste a fair amount of time trying to collimate under poor seeing conditions. Something that would allow me to do this in the day and not rely on seeing conditions would be of extreme benefit. I did read up on both the Ocal and Hotech; the Hotech being the gold standard apparently of collimation devices for SCT's but with a hefty price tag. I won't mind spending the money on either one if they truly yield good results, the reason im looking more at the Ocal is it seems like less of an overall process allowing me to collimate before each viewing / imaging session. Other thing that scares me with the Hotech is it involves removing the secondary mirror and also shifting the corrector plate around; which as a newbie seems daunting. However if this just sounds scarier than it is I would be open to it.

 

I did some preliminary research and found some articles here on CN about it but there isn't a ton of different user feedback and it seems to be people got it to work and thought it was fine (maybe some final tweaks on a star afterward) or they couldnt get it to work at all; but I believe this was on the earlier versions.

 

Any thoughts (on either) would be great. Thanks!


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#2 cookjaiii

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Posted 12 February 2024 - 10:39 AM

You can try using an artificial star indoors if your outside seeing isn't stable enough, but some folks report that the collimation may change when you raise the altitude from horizontal.  This is probably due to mirror flop.  This may or may not be a problem for your particular telescope, but it works for me.

 

This is the easiest to follow description of Sct collimation that I have found (Sct directions are about half-way down the article.

 

https://uncle-rods.b...ollimation.html

 

Best of luck with your quest!



#3 gfstallin

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Posted 12 February 2024 - 10:47 AM

Vinny, 

 

I don't have any experience with the Ocal. I do have experience with artificial stars. In my experience, they aren't perfect, largely due to slight mirror flop, but they got me very close to perfect collimation for general purposes. Your results might vary, particularly if you have more or less mirror flop than my SCTs do (negligible in C6 and C8, noticeable though manageable in a C11). If you are doing high resolution imaging, you'll want to use a real star; however, I'd argue that if seeing is not good enough to get perfect collimation on a real star, you will not get any improvement over what you achieved with an artificial star anyway. When I lived in a large condominium with 105-foot (~32 meters) hallways, I'd set up my SCT and an artificial star in the hallway and collimate in indoor comfort. Perhaps the real benefit to doing this is it got me comfortable enough tinkering with collimation so that when decent seeing presented itself, I felt comfortable enough to adjust collimation relatively quickly and painlessly on an actual star near the planet I wanted to image. 

 

George


Edited by gfstallin, 12 February 2024 - 10:48 AM.

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#4 Vinnyvent84

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Posted 12 February 2024 - 10:50 AM

You can try using an artificial star indoors if your outside seeing isn't stable enough, but some folks report that the collimation may change when you raise the altitude from horizontal.  This is probably due to mirror flop.  This may or may not be a problem for your particular telescope, but it works for me.

 

This is the easiest to follow description of Sct collimation that I have found (Sct directions are about half-way down the article.

 

https://uncle-rods.b...ollimation.html

 

Best of luck with your quest!

Thank you I am going to check this out!



#5 Vinnyvent84

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Posted 12 February 2024 - 10:54 AM

Vinny, 

 

I don't have any experience with the Ocal. I do have experience with artificial stars. In my experience, they aren't perfect, largely due to slight mirror flop, but they got me very close to perfect collimation for general purposes. Your results might vary, particularly if you have more or less mirror flop than my SCTs do (negligible in C6 and C8, noticeable though manageable in a C11). If you are doing high resolution imaging, you'll want to use a real star; however, I'd argue that if seeing is not good enough to get perfect collimation on a real star, you will not get any improvement over what you achieved with an artificial star anyway. When I lived in a large condominium with 105-foot (~32 meters) hallways, I'd set up my SCT and an artificial star in the hallway and collimate in indoor comfort. Perhaps the real benefit to doing this is it got me comfortable enough tinkering with collimation so that when decent seeing presented itself, I felt comfortable enough to adjust collimation relatively quickly and painlessly on an actual star near the planet I wanted to image. 

 

George

Thanks George! I looked into that as well and very appealing! problem for me is it would likely have to be outdoors and like you said due to mirror flop I beleive they suggest you keep the scope at 45 degree angle when doing it. I have a private residence in Brooklyn NY but I think you need about a 100ft as you did, therein lies the problem. Getting the flashlight star elevated enough and far enough is an issue. Inside my home would be impossible. Outside maybe if i put the star in a second story window and then go into my neighbors yard (they wont mind! lol). Definitely doable but when you look at the Ocal videos it makes it seem SO MUCH easier but I come here for feedback because you cant always believe what you hear / see on these videos. 



#6 dcweaver

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Posted 12 February 2024 - 11:50 AM

Vinny -

 

Ocal is one of many tools that are helpful for "rough" collimation, but won't guarantee good "fine" collimation. Using a tool like that, or just centerIng an "out-of-focus shadow" is a good starting point, but it has to be followed up by working toward "in-focus" stars at high power to achieve the best result. The objective is to get a "symmetric" Airy pattern (no on-axis coma) for an "in-focus" star (first diffraction ring centered and symmetric around the central Airy disc). The article that @cookjaiii pointed you to is a good one. Pay specific attention to the "fourth" step at the end.

 

https://uncle-rods.b...ollimation.html

 

The next link is to a video that shows why centering an "out-of-focus shadow" does not always leave you with a collimated scope. The relevant discussion starts at the 11:04 mark.

 

https://www.innovati...ricalMirror.mp4


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#7 speedster

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Posted 13 February 2024 - 02:14 AM

A good way when seeing isn't cooperating, or any other time, is to use Metaguide.  It uses an in-focus star and takes the guesswork out.


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#8 Vinnyvent84

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Posted 13 February 2024 - 05:48 AM

Vinny -

 

Ocal is one of many tools that are helpful for "rough" collimation, but won't guarantee good "fine" collimation. Using a tool like that, or just centerIng an "out-of-focus shadow" is a good starting point, but it has to be followed up by working toward "in-focus" stars at high power to achieve the best result. The objective is to get a "symmetric" Airy pattern (no on-axis coma) for an "in-focus" star (first diffraction ring centered and symmetric around the central Airy disc). The article that @cookjaiii pointed you to is a good one. Pay specific attention to the "fourth" step at the end.

 

https://uncle-rods.b...ollimation.html

 

The next link is to a video that shows why centering an "out-of-focus shadow" does not always leave you with a collimated scope. The relevant discussion starts at the 11:04 mark.

 

https://www.innovati...ricalMirror.mp4

Thanks for the feedback Dcweaver. The video is also helpful, I see what you mean after watching it. Do you use that skywave software or stick with strictly visual? I also see Bahtinov masks or Tri-Bahtinov masks frequently mentioned, is this too like the Ocal in relation to just being good for rough collimation or a starting point or actual a real means to an end of achieving collimation? I have seen countless youtube videos of SCT users using the mask and once they get the spikes lined up they consider themselves good to go both for visual or imaging. Now just because theres a ton of videos demonstrating that doesn't mean its the right way and I understand that but just because of the sheer volume of them that I have seen I figured I would ask. 


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#9 Vinnyvent84

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Posted 13 February 2024 - 05:50 AM

A good way when seeing isn't cooperating, or any other time, is to use Metaguide.  It uses an in-focus star and takes the guesswork out.

Hey Speedster, thank you. I am actually reading some tutorials now on Metaguide and looking at some videos. It looked a bit challenging to use but maybe thats just me so I figured let me brush up a bit before I try and actually use it. Do you find it easy or challenging (at least in the begining) to use?



#10 tturtle

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Posted 13 February 2024 - 08:35 AM

I looked into this Ocal thing a while back and it seemed to me that it wasn’t any better than a carefully setup daytime collimation using a pinhole. The key to the daytime method is the pinhole, which fixes your view of the concentric rings in perfect alignment with the OTA and gets it probably 98% aligned. Critical to this is carefully setting up a perfectly aligned viewpoint rather than just standing in front of the scope and “eyeballing” it.  The steps are:

 

1. Set up the scope on a firm surface and use a bubble level to get the OTA perfectly horizontal and level.  Measure the distance from ground to the exact center of the OTA.
2. Get a tripod and attach a piece of cardboard with a pinhole in it and adjust the height of the pinhole to exactly match the height of the center of the OTA. Pull a string along the OTA or use a laser to set the horizontal position of the pinhole/tripod in line with the centerline of the OTA.  Set up this tripod about 10 or 15 feet away from the scope.  You now have a pinhole that is perfectly in line with the optical centerline of the OTA (assuming you have been careful with your setup). This will give you a perfectly aligned viewpoint to see the concentric rings when looking into the front of the scope.

3. Look through the pinhole into the front of the OTA and view the concentric rings carefully noting any misalignment. Try moving the pinhole/tripod away from and towards the OTA to make all the concentric rings easier to see.
4. Adjust the collimation screws to get all the rings you see inside the OTA (the so called hall of mirrors) perfectly centered.

 

I used this method on my 9.25 SCT about 5 years ago and got the collimation nearly perfect without any further tweaking. Several months ago I viewed Jupiter with my binoviewer on a particularly good night and was able to see the moons as disks, albeit very small, rather than just points of light. That’s good enough for me. 


Edited by tturtle, 13 February 2024 - 08:48 AM.

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#11 dcweaver

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Posted 13 February 2024 - 02:55 PM

Thanks for the feedback Dcweaver. The video is also helpful, I see what you mean after watching it. Do you use that skywave software or stick with strictly visual? I also see Bahtinov masks or Tri-Bahtinov masks frequently mentioned, is this too like the Ocal in relation to just being good for rough collimation or a starting point or actual a real means to an end of achieving collimation? I have seen countless youtube videos of SCT users using the mask and once they get the spikes lined up they consider themselves good to go both for visual or imaging. Now just because theres a ton of videos demonstrating that doesn't mean its the right way and I understand that but just because of the sheer volume of them that I have seen I figured I would ask. 

Vinny -

 

I have only done high magnification Airy patterns, but SkyWave and Metaguide are what I consider "gold standards" because they directly quantify on-axis coma. SkyWave also quantifies spherical aberration and astigmatism.

 

The Tri-Bahtinov is an interesting idea that has "internet" credibility, but I have not run across any studies that give it "genuine" credibility, just a lot of anecdotal evidence. That said, I am a fan of innovative thinking, and it is easy enough to collimate with it, then check the in-focus Airy pattern at high magnification. If someone wanted to dig deeper, they could check the final on-axis coma with Metaguide or SkyWave. Since I plan to adopt SkyWave in the future, I may intentionally introduce some tilt/tip/offset, collimate with a Tri-Bahtinov, then check results with SkyWave to see if there is any real substance to it.




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