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Hi everyone, I'm struggling with getting my 6" RCT fully collimated so I'm always ending up with some corner of my images being somewhat distored/out-of-focus Most recent example: https://www.astrobin.com/372110/ - top left corner For the most part, I've been following the guide by Han Kleijn at http://www.hnsky.org/RC_collimation.htm Specifically: - I'v tried to make sure that the primary mirror is square to the focuser assembly. As reported by many other users of this telescope, the primary mirror assembly had a bit of wiggle-room and I increased the thickness of the plastic ring with a bit of duct tape so that the mirror is now sitting tightly and square to the focusser. - Using a Baader Laser-Colli Mk.3 I aligned the focuser axis with the tube axis by removing the secondary mirror and with a piece of tssue over the screw-hole ensured that the laser point is in the middle using the adjustment screws on the focusser assembly - Adjusted the secondary by ensuring that the laser is reflected back to the middle of the collimator - Re-checked primary/focuser adjustment by ensuring that the laser hits the center mark on the secondary my looking at the reflection in the primary - When I look into the scope w/o an eyepiece with one eye so that my pupil is reflected in the center mark of the secondary, everything looks like it lines up perfectly - When I put a white dust-cap in the focusser and look into the front of the tube from 2-3 meters away, I see the thin white rim reflected in the primary fully symmetrically So far so good... Now, when I mount my camera (Sony A6000) and check how a defocussed star looks like it's quite unsymmetrical in the center of the viewfinder. I can get it symmetrical by moving the star to a place (pretty much to one corner) where it looks right and then adjust the secondary to move the defocussed star back to the center where it will then look symmetrical. I checked focus with a Bahtinov mask in all four corners and that looked good. However, when taking pictures that will the result in the kind of problems described above (one corner defocussed) When I look into the focuser without an eyepiece now as described above, things look way off :-( I tried to make sure that there is as little pull on the focuser as possible by using proper extension rings between OTA and focuser. On the other hand, I don't know how much these darn clamping connections are prone to tilting... I try to tighten the screws on the focuser as much as possible and the 2" connection for the camera adapter does look pretty solid as well... Any ideas? |
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Hi, Personally, I had this problem, precisely on my last M33. I have my GSO RC of 6 "well collimated (it can always be improved) but due to a bad alignment of the optical axis when mounting the camera (Canon 1100D) I have a slight blur also in the left corner, when tightening the camera / focus connection screws we must control that there is no inclination of the optical axis, however minimal, I recommend reviewing this issue. Greetings. |
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I've had a single blurry corner before. I was able to correct it by adjusting the primary. Most of the collimation adjustments you're making are to mechanically align the primary to secondary. But the scope typically requires some additional alignment once the optical train is assembled to get the primary and secondary optically aligned. I've used the linked method attached to very successfully fix that blurry corner by adjusting the primary with a bahitnov mask to adjust each image corner one at a time. https://deepspaceplace.com/gso8rccollimate.php Here you can see the blurry upper left corner : https://www.astrobin.com/362294/. And fixed image here: https://www.astrobin.com/346061/B/ Hope that helps. |
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I post here almost 3 years after the original post, but I found this method to collimate our small RC that have a focuser directly linked to the primary mirror (no individual adjustment possible) : http://www.365telescopes.com/how-to-collimate-an-rc-the-williamson-method/ It has worked very well for me. Just be careful when unscrewing the secondary and moving everything : it could fall on your primary. |
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| That's neat. Thanks for the link, Jérémie! |
