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We all know the reputation these scopes have when it comes to collimation. As a former RC owner I always wondered if collimation was really that difficult on an Epsilon or if people just aren't using the correct method. I've owned an OCAL v2 for a while now and used it to collimate my 10" F4 ONTC and it does a fantastic job. Not only is it more precise than I could ever be with a laser and cheshire, but the convenience of not having to look down a drawtube is pretty sweet especially when you're tall like I me (6'3"). I posted a pretty high level overview on that experience HERE for anyone interested. I'm going to try and keep this as brief as possible. Anytime someone brings up collimating an Epsilon with anything other than the Tak tool they are quickly jumped on and told they are wrong. I've found a few posts from individuals saying they collimate their Epsilon with the OCAL and the result is always the same.. "DONT USE THAT!". But I never understood why not. The Epsilon is a Newtonian telescope. Yes its fast. Yes it has a hyperbolic primary mirror. Yes it has an offset secondary, but do does my ONTC. I don't see why the OCAL wouldn't work if used correctly. When it came time to purchase my own Epsilon I took the safe route and also purchased the Tak collimation tools just in case. I used it for about 2 weeks. I didn't find collimation to be very difficult with the tool. Between the Tak manual and @Bill Long - Dark Matters Astrophotography 's E160 collimation guide (LINK) I felt like I had a pretty good understanding on what needed to be done and how to do it. I got the scope, rotated the focuser to the position I intend it to stay at permanently, collimated as best I could with the Tak tool, and tuned out the sensor tilt as best I could with the ASG tilt cage. Overall I was happy with the results I've been getting but the corners still had more tilt than I liked. BlurX does a pretty good job at cleaning that up but I would prefer to not have to rely on software to fix hardware issues when possible. Eventually I found myself back to thinking the OCAL should work. So I took a chance, ordered an OCAL v3 MAX and set out to find out once and for all. The result... The OCAL 100% works and can be used to collimate an Epsilon 130. So I would imagine it can also be used on the 160 and 180. Full disclosure: All results here are with an IMX571 APS-C sensor. If someone wants to send me a full frame camera for me to test I'd be more than happy to 😂. First of all I want to show the result I was able to get with the Tak collimation tool. Perfect? Probably not 100% but I think it is within tolerance. The stars I was getting in my data definitely suggest so for the most part.  Setup: I installed the device using its 1.25" nosepiece adapter and inserting that into the Tak eyepiece compression ring. The sight tube was not installed. If able, the ocal should be threaded into the focuser instead of using a compression ring. M60 male to M42 male adapters aren't very hard to find. I used a large drawing pad on a music stand as my light source to be able to see what I'm doing. Collimation was performed on my office desk during the day. The OCAL is sensitive enough that pretty much any daylight will be enough if outside. Even a completely overcast sky.  The OCAL:First we need to talk about how the OCAL works. It is literally just an electronic sight tube / cheshire. It gives you 3 digital rings which you can change the size and color of each to match it to whatever part of the optical system you need. It also gives you a digital crosshair. What color you use is a personal choice. I like yellow and light blue because they are the easiest to see contrasting against the surface I'm trying to align. The goal here is the same as with any other Newtonian telescope which is to: a) Align the optical center of the secondary mirror to the center of the focuser. b) Align the optical center of the primary mirror to the center of the focuser. The Mechanics:Now we need to understand exactly how the OCAL interacts with the mirror spots. Since with the OCAL your crosshair is "inside" the camera instead of physically in the drawtube as it is with the Tak sight tube, things move differently. It should also be noted that per the OCAL manual every unit has a different serial number. That serial number corresponds to a code on a spreadsheet that OCAL provides that you need to entire in order to calibrate the device. As seen on the OCAL display... Secondary mirror screws - Moves the secondary spot AND the primary mirror circle. Primary mirror screws - Moves the reflection of the eyepiece that is inserted into the focuser (what's holding the OCAL sensor). You can see the camera sensor at the middle of the eyepiece.  Step 1: First we focus the camera so that the end of the drawtube is in focus. Then using the offset sliders to align the first circle with the end of the drawtube. This is a crucial step! If you don't take time to ensure the OCAL display is centered in the focuser no adjustment you make going forward will be valid. Here you can see my first ring is concentric with the focuser drawtube. Is it absolutely perfect? No. But I am zoomed in as far as the camera will allow so the size of the error is very small. So small it would be undetectable by the naked eye looking through an pinhole eyepiece. Now that we have confidence that all the OCAL rings and crosshair are centered in the focuser, we can start adjusting the mirrors.  Step 2: As with the Tak tool our first step is to center the secondary spot. Enable the OCAL crosshair then focus the OCAL on the secondary spot then loosen the secondary locking screw and collimation screws and by hand center the secondary spot on the crosshair. Once you're there snug up the locking screw and collimation screws so that the mirror stays put.  Step 3: Enable circle #2 , size it to be a little larger than the primary mirror circle. We are using the gap between the blue circle and the outside edge of the primary mirror circle as our reference points. Using the 3 secondary collimation screws, adjust the secondary mirror's tip and tilt until the primary mirror circle is concentric with the blue circle.  Step 4: Lastly, enable the third OCAL circle (red) and size it so that there is a small gap between it and the inside black edge of the eyepiece. Adjust the primary mirror push/pull screws to make the black ring concentric with the red circle. Make sure the mirror is locked down when done without throwing off collimation.  At this point collimation is done. We have ensured that the OCAL circles and crosshair are concentric with the focuser. The secondary spot is centered on the crosshair. The primary mirror circle is concentric with its circle (blue). The OCAL body/Tak adapter in the focuser is concentric with its circle (red). Thats it. I would consider this to be a pretty simple process. Getting your computer set up and the focuser circle placed right takes more time than the mirror adjustments. As with the Tak tool this can be done indoors during the day or even out in the field. I have performed this task in my backyard, in the field, and in my remote observatory. Results: Pixinsight aberration map  Center  Top Left  Bottom Left  Top Right  Bottom Right  Perfect corners? No, but it is a significantly better result than what I was able to achieve using the tak tool alone. I also still have a small amount of sensor tilt but I would call these good stars. Here's what Hocus Focus and ASTAP have to say about my tilt and back focus error. The back focus error I'm happy content with. A 0.009mm error is too small to be concerned with even at this f ratio. I did my best with the tile but even with the ASG cage the adjustments start getting so small that they are just really difficult to make by hand. ASTAP is reporting 5% tilt. I can live with that. There is still BlurX. It should be noted that while more accurate the OCAL does take a little more time to use. In the time it takes for me to log into my laptop, connect the camera, adjust the offsets, and get going, I could almost be done with the Tak tool. The MAX version of the OCAL does allow use with some Android and iOS devices which is nice for field collimation but those that are already getting really good results with the Tak tool may not find much practical use for the OCAL unless they really hate looking down the focuser the old fashioned way like I do.   |
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| Great post. Wish I hadn't sold my OCAL now! ;-( |
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Dunk: Thanks! I figured if for some reason it didn't work u could still use it on the ONTC and any other bmneet I own in the future. |
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I dont own any of this, but I enjoyed reading the post. And I like when poeple get result using a different path. K. |
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Hello and thank you for this very complete and interesting tutorial. I have a Newton GSO TRUSS at f4 with great difficulty collimating it correctly. I have an ocal. When I collimate using this tool, I get very poor results on the stars. After collimation at the ocal, when I slide my very good quality collimation laser, the laser spot is offset from the center of the primary mirror, and of course, it does not return to its original point. When I do the collimation with just the laser, it works pretty well, but it's far from perfect. I'm thinking of trying your technique. I'll let you know if it worked well for me  |
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Frédéric Tapissier: I have owned 2x GSO 10" F4 newts. I didn't have the OCAL at the time. I would collimate using a Farpoint laser and cheshire. The reason I sold those scopes and got the ONTC was because the GSO primary mirror cell is garbage. The entire cell would bounce like a spring when the scope slewed ruining collimation. I thought maybe I just had a bad cell but the second scope did the exact same thing. The ONTC and Epsilon on the other hand do not lose collimation unless I drive with them. Cheap Newts really are more trouble than they're worth IMO. |
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| Great write up! I have had the Ocal collimator for a while. I always preferred to use the threaded connection though because I worry about minor shift when getting it in with the nose piece. |
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Ashraf AbuSara: A threaded connection is definitely preferable I just haven't taken the time to figure out how to make that happen yet. |
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| Excellent post and results! I have the Rigel Aline collimator and will test it out on my E160. |
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| Do you save your AF runs from NINA? If so, it would be good to run through ASTAP Hyperbolic Curve Analysis. I've found the results to be slightly better than NINA with respect to backspacing and to a lesser extent tilt. Also, keep in mind that any backspacing measurement by NINA or ASTAP is an optical backspacing calculation based on focuser position deltas.... it's not computing the actual backspacing error, so it may not match the amount you "should" change in real life. Nice work! |
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Reg Pratt:Ashraf AbuSara: Shouldn't any M54>M42 adapter work with the corrector? |
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Chris White- Overcast Observatory: Yes my AF runs save by default. Though the Hocus Focus plugin requires you to use its own software to run and analyze the vcurve instead of the default NINA AF. I can run some of my results through the hyperbolic curve analysis. I would expect that given the state if the stars on and off axis that whatever numbers are output I must be within tolerance of the target back focus. As much as I love looking at numbers, at the end of the day my judgment is based on how good a star field actually looks in focus and I have to say this is the best result I've achieved on any telescope I've owned be it Newt, RC, SCT, or refractor. This is also the first time I've actually bothered to address sensor tilt too though 😅. Ashraf AbuSara:Reg Pratt:Ashraf AbuSara: Collimation is done without the corrector installed so you'd want to use an M60 male to M42 male adapter. M60 being the thread size of the focuser. The focus range on the OCAL sensor isn't very big so I can't say if you'd be able to reach focus in all the places necessary if threading the device directly to the drawtube. If I were going to do this (and I likely will eventually) I would also use m42 spacers between the OCAL and M60 adapter to make everything the same height as it is when using the OCAL nosepiece simply because I know for sure that spacing works. |
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Reg Pratt:Chris White- Overcast Observatory: Oh interesting! Why can't you collimate it with the corrector on? |
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Ashraf AbuSara: Well in the case of the Tak tool the sight tube needs to protrude into the focuser drawtube and the correctors would prevent that. In the case of the OCAL maybe the corrector could be kept in during collimation but I remember the owner of OCAL stating to remove Newt correctors for collimation so that's what I've always done on the ONTC and what I did here since you have to do that anyway when using the Tak tool. |
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| The reason i bring up the backfocus limitation of the software, is that any spacing error will compound with tilt error. Simply by dialing in the spacing, you may mostly fix the effect of tilt. I've used both astap and hocus focus extensively with epsilon. Both will guide you to a very good result, but both also have limitations. |
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Reg Pratt:Ashraf AbuSara: The manual seems to recommend connecting it to the threads of the corrector, unless you have trouble with clarity.  |
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Chris White- Overcast Observatory: I appreciate the info and will check that out. Thank you! Ashraf AbuSara:Reg Pratt:Ashraf AbuSara: I will admit I never read the manual, only watched the YouTube video. New users should definitely try it with the corrector in then. I think I will continue to use it without the corrector though because I already know it works that way. |
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Reg Pratt:Chris White- Overcast Observatory: Yes of course if it ain't broke don't fix it  . This is all wonderful information thanks for the write up. I still don't own the epsilon, but I plan on getting a 160ED and build a setup for a remote hosting site, and doing all the research needed to create that setup. Btw any suggestions on coupling the EAF with the Tak focuser? It seems most Epsilon users say that a Opetec Leo focuser is a must. Have you had any issues with the EAF? Where did you get your coupling? |
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Mind you I've only been using the scope for about 2 weeks now. In that time I've gathered close to 30 hours worth of data and have had zero issues with the stock focuser or EAF. I've been told that the 130 focuser has been updated recently and is much better than the old once. I've not experienced any rigidity issues at all. The EAF doesn't come with the required coupler though. You can grab the needed 5mm to 8mm flex coupler from Amazon for very cheap. |
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| @Reg Pratt great write-up! and thanks for trying something new for all our sakes I have an ocal that I had practically retired, but perhaps it's coming out again next time it's collimation day |
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| @Nick Grundy aside from the difference in reference points compared to a parabolic Newt nothing really changes in the process so you should be able to use it well. I definitely noticed when I was doing my pre-purchase research that those few people saying they successfully used the OCAL with Epsilon never posted any results so I just wanted to get some out there instead of continuing the "it works!" "no it doesn't!" cycle that seems to repeat anytime this topic comes up. |
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I would also like to point out that the OCAL exposed the fact that my Tak crosshairs were not installed well the first time. If this had gone undiscovered I would have been spinning my wheels as to why collimation looked good in the eyepiece but didn't reflect in star fields. The photo of the Tak tool collimation posted above was after I reinstalled the crosshair threads with a second set of hands to make sure the threads were tight. If anyone out there is a visual learner and wants a video of the procedure let me know and I'd be happy to record one. |
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| Great review! Although mine is quite well collimated I think that since it is going to be installed at a remote site this would potentially be a great help if it got out of collimation since I could view remotely and have the adjustments done by the tech. Just ordered one. |
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| @Bill McLaughlin that's an interesting way to use it! When I installed my remote scope I taught them how to use the OCAL and just left it there since at the time I didn't have home scope. That's the main reason I ordered the newer version. |
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I have the Hyperstar 6, the Ts version of the Epsilon 160 but with a 150 mm mirror. Its REALLY a pain to collimate even with the Hotech 1,25" SCA Laser Collimator. Your demonstration is more than convincing. I feel like I'm going to try the OCAL despite its high price here in Europe. Maybe I'll FINALLY have stars that don't look like a herd of Halley's Comets ! Next month perhaps. For the moment, the sky looks again like a inalterable grey blanket over my backyard and my banker is in a bad mood ... |
