You don’t “need” any collimation tools for an RC. I’ve been using the DSI method. It’s similar to an SCT collimation with 2 steps. It’s arguably better than using any tool since using a collimation tool makes assumptions about the mechanical alignment of the mirrors. With the added bonus of being free of course. It’s over looked too often.
Thanks for the video! You are a very patient person. Those cheap RCs have the main mirror attached to the focuser. That's a major source of issues. And the focuser is of poor quality. I'll stick to my refractors. An 8 inch SCT completes my line-up for smaller objects. They also need collimation but it's so much easier to do.
Warning, NEVER find the distance between primary and secondary assuming that the specified focal length is correct. This measure is never the same in 99% of cases. The only trick to consider to adjust this parameter is the backfocus. The camera must be in the focal plane at exactly the prescribed back focus (254mm in my GSO 8") and focus must be found the first time by adjusting the forward/backward position on the optical axis of the secondary mirror. In my case I have got a focal length shorter than the standard (1604mm instead of 1624) but I eliminated the spherical abberation completely. If you dont know tthis number you can use a ronchi reticle to find this distance between the primary and secondary mirror. At the end just for curiosity you can use the plate solving to know the focal lenght of your system. I heard that this number is written under the primary mirror. I haven't checked yet.
Great video very informative. I have wanted an RC for a while and this video has made me much more confident in buying one because I read that collimation was hard. Thanks for sharing :)
Thank you for the collimation video, very helpful. Pretty much every collimation video I've viewed recommends adding a focuser tilt ring if one isn't already installed. Your video treats tilt after collimation as opposed to being part of the initial collimation process. I think I like your approach better, if it ain't broke, don't fix it. Either way it seems collimation is affected so I assume this will be somewhat of an iterative visual process with very small adjustments, any thoughts on that? Also, since I have in the past adjusted the tilt ring as part of the collimation process, I'll share in my experience that the adjusted tilt ring does create a light leak, so I apply black electrical tape around the two rings of the tilt plate to alleviate the potential introduction of unwanted light.
3:00 your warranty CANNOT be voided in the US unless it is proven ehat you did caused the damage. If you remove the primary and the glue or coating on the secondary fails you are still meant to be covered. I honestly prefer building my own equipment.
Hello, First thank you for this good video and explanation. I think such videos are very helpful. :-) As you mentioned, we should give feedback and questions which I would like to do. I have two questions / comments: 1) Checking laser-adjustment itself. If I see the picture right, you are putting the laser to another instrument (a refractor telescope) and watch the laser spot that has passed this instrument. In this configuration potential misalignments of this instrument can also make the laser spot rotating. If this is the case, there might be the risk to de-adjust the laser. The laser beam direction is then not parallel to the housing of the laser. This is - as you said - not good for using the laser to adjust the RC instrument or any other instrument. My proposal would be to mount the laser in an eyepiece that is fixed on the table (without any other optics) a watch the laser point on the wall then. I think in this configuration any movement of the point is then in deed caused by a misaligned laser and can be corrected by adjusting the three screws of the laser-tool. What do you think about this? 2) Adjusting the distance between the main and secondary mirror using plats solving. The distance between the two mirrors are critical - yes. However, should the goal really be to have the final focal length adjusted to the value that the instrument should have as written in the spec? When the main mirror and the secondary mirror are produced, there is always a deviation to the focal lengths that it should have. However, the best optical performance is achieved if the two real focal lengths of the two hyperbolic mirrors fit together. The resulting overall focal lengths of the instrument could be different than what is written in the specification. If the distance of the two mirrors is adjusted in a way that the total focal lengths is according to the spec, it is possible that the two shapes do not fit to each other in an optimal way, right? To find the optimum distance, I think a different test set-up is required that uses monochromatic light wave patterns or pictures of the stars. Both is much more time consuming. I am interested to see also comments from the others ;-) Regards Jens
Plate solving for mirror spacing is a rough way to get it right, you can also get a Ronchi Eyepiece which can provide very accurate feedback on mirror alignment but can be tricky to learn how to use. Good video and keep at it.
6:50: I'm a little confused how you align the laser with itself. Are you pointing the beam through another telescope and onto the wall? Also, of course the laser spot is going to rotate if you rotate the laser. Do you mean make sure it doesn't wobble from center position? I bought a cheapo laser collimator on Amazon and I have doubts that it is aligned properly. So I need to start with this.
I have a 6" RC and it is very well collimated but the small stars come out in the shape of an egg and some others are diffuse in the same way as an egg. Would it be necessary to adjust the rear mirror to correct this problem with the fixing screws? back?
It's probalby worth giving the collimation a check. Check if a out of focus star in the center is circular. If the stars in all the edges show the same shape, you should check for tilt of the focuser
I didn’t know you could collimate it with this type of laser!! The one I’ve been looking is out of stock everywhere, so I’ll definitely look into this one
I have a question if I may. If your focal length is too long (after removing the primary mirror and cleaning it) and you need to shorten it, do you move the secondary in or out? Great video, thanks!
I did not understand that either. Simply tried it out. It's kinda counterintuitive. My guess would be that moving it in shortens the effective focal length, but I don't remember anymore
I am currently struggling with my 8" RC. I have questions regarding setting the focal length and the star test and would welcome comments from anyone, not just Tim. An ASIAir was used in the video to tell what the approximate focal length was. Does anyone have a recommendation for something other than ASIAir? I use a QHY camera with my RC and it is obviously not compatible with ASIAir. As for the star test, it was mentioned about the rings not being concentric, but they looked decent. That my have been after the adjustment for all I know. I have seen many articles and videos on the topic of the star test and they all conflict. Even the instructions from different manufacturers don't agree. Some say to adjust the secondary while other say to adjust the primary. I adjusted the secondary and was able to get my rings concentric and in the videos, the primary was adjusted and appears to have accomplished the same thing. So which is it really and why?
Plate Solving can be done with almost every imaging software. If you don't own any of those, upload your images to astrometry. Regarding the concentric rings. If you deocus, the dark circle in the center is the secondary. YOu want to move only this circle, and not all the other ligth that's coming in. Imaging looking through the OTA without accessoires. The only way to move the only black circle in the cneter, the secondary, is to move the primary
Hi! Can you share the link for the tilt adapter? I found one at TS - "TS-Optics M90 Tilting Adapter Flange for astrophotography", it says it is for the RC8 and 6, but I am not sure. I bought an used OImegon RC6, but it has not been arrived yet
Hi, ich habe mein RC 8 mit Ocal Pro justiert, aktuell ist alles zentrisch die Sterne sind rund bis in die Ecken. Tatsächlich ist die Mittenmarkierung des Sekundärsspiegel nicht exakt mittig- soll wohl normal sein-, da bin ich etwas irritiert was die Justage mit Lasern angeht . ASI Air sagt nach dem Platesolve 1613mm Brennweite bei 1624mm... ob da so verlass auf die Genauigkeit ist wag ich zu bezweifeln. Was mich ebenfalls irritiert ist der längere Fokusweg vom OAZ gegenüber dem nicht justierten Zustand. Aber gut das Bild ist scharf und die Sterne sind rund. LG Lara
I also bought that TSRCKolli device after using a DIY solution with an ESP32Cam and a plastic waterpipe. Why do I have to remove the distance rings before collimating? I always collimate in final setup condition and just replace the collie with the DSLR. That tilt adapter will be my next investment. One more question: I did this secondary distance adjustment by loosening the large ring behind the spikes, turning the holding tube so it moves in/out and then tightenin the ring. Should I instead screw it completely down and use the center screw? There should be a Discord server for RC-Users to exchange experiences and help each other :D
I you leave the adpaters on, the Kolli will be too far away from the OTA to look past the baffle. At least I could not see the rings with extensions on, and the manufacturers recommend it as well. I know about the method to rotate the baffle, but it was completly stuck in my case, so I came up with the screw-idea. And a Discord server? Why not right here? :D discord.gg/MXMnjwjA
Hi Tim. I have a sky watcher 250 dob synscan. I have sent my mirror to orion optics uk for a coatings upgrade. When I took out the primary marked the top point so mirror goes back in same way as it was. I noticed that where the previous owner has collimated the screws are almost fully in which is at end of travel and restricting proper collimation. If I back them off and start again am I looking for a disaster?
