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Sweet... I mean, you really haven't lived until you've collimated a hyperbolic newtonian.  Time to wait for some clear skies.... and maybe a photon cage... In case anyone else is wondering (because I really didn't see anything describing this): To get the crosshairs centered, I had to loosen the secondary mirror screws quite a bit, while maintaining some tension with the locking center knob (giving me more room to pull the mirror up towards the objective opening on the scope). I guess when I was trying to collimate initially, I tightened them way too much. This led to a lot of my frustration because, for the life of me, I couldn't figure out how to get the crosshairs centered on the circle.  |
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There is a video on YouTube of this (and he REALLY loosens it - way more than you need to). Also there is a very good tutorial on collimating the 'nana here on astrobin by Bill Long. |
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Dunk: Yup, saw both, but I don't recall anyone stating that loosening the secondary screws is what would make the crosshairs shift right, but maybe I missed it. I do recall someone saying that you didnt need to worry about their alignment - that they dont normally align, but maybe that was in reference to the spider cross. |
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Dunk: Possibly. I would check it for stability and see if it holds collimation after being used for a while (maybe 2-4 nights) and has been moved and parked in various positions. I have had collimation slip on occasion for reasons I cannot pin down (before someone suggests it - not a loose primary or secondary). OTOH, if it stays after a week or so it will probably stay indefinitely as long as it is not bounced about shipping or moving it. In fact, mine has been off and on the mount about 4 times in the past week since I got a new mount and needed to get everything wired/configured. I just checked collimation last night and it held well . |
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Bill McLaughlin:Dunk: Yep, definitely. Took it out last night and (even though the seeing was horrible and there was a lot of atmospheric turbulence) after I figured out that my back focus was slightly off, I had pretty solid diffraction spikes (no double spikes) but still have tilt (and ccdinspector shows that I can still improve on collimation). going to check and recheck collimation and try to dial it in a bit more. I’m also heavily leaning towards getting a Leo… autofocus was horrible in Nina and I was able to get it better focused by manually selecting a position (could be my settings in Nina). also still waiting for the photon cage to arrive. still learning the ropes but I will say this: collimation on this scope definitely seems more robust than on my C8. Now I need to get over my fear of touching the primary… it’s not documented very well. |
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NINA's autofocus routine, if you have tilt or significant backfocus error, can sometimes give incorrect results as it measures star size across the whole field. Instead of a nice tight curve with relative small error bars: You might instead see a flat bottom with large error bars where it is unable to determine the precise smallest hfr position since it varies largely across the frame. Using the ROI setting in the AF settings can help clean this up as it excludes off axis sections of the field.  Collimating the primary is actually a lot easier than the secondary in my experience. While secondary collimation involves a lot of sticking your whole hand onto the mirror and trying to hold it in place while simultaneous staring down an eyepiece and tightening the right screws (and if you're me, not dropping your tools into the tube); primary collimation is simply about aligning the reflection of the focusing cap (black circle outlined in red) to the primary mirror mark (black circle outlined in green). The white spacing (with purple lines) should be equal around the donut.  The blue donut is the secondary optical center mark, it being misaligned is probably why your illumination is slightly off center. In your case the primary mark isn't perfectly positioned also. I would collimate the primary by mounting the scope on my EQ mount, slewing to zenith during the daytime (obviously when the sun wasn't shining on the scope), and loosening all the push and pull screws (and the side screws further securing the mirror cell) to a point where the mirror cell would have a lot of give (about 1 cm). Then I would go around and around slowly tightening each of the three larger screw while keeping the position of the two circles in alignment - once each screw was about as tight as it could get I'd snug up the 6 smaller screws. |
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I would collimate the primary by mounting the scope on my EQ mount, slewing to zenith during the daytime (obviously when the sun wasn't shining on the scope), and loosening all the push and pull screws (and the side screws further securing the mirror cell) to a point where the mirror cell would have a lot of give (about 1 cm). Then I would go around and around slowly tightening each of the three larger screw while keeping the position of the two circles in alignment - once each screw was about as tight as it could get I'd snug up the 6 smaller screws. Your entire post is INCREDIBLY helpful! Thank you! My concern with the primary was 100% related to how it is described in the manual. The schematics didn't match what I had, and after reading this post, it totally makes sense how I would do this now... So, just to summarize, to get the football centered, I should just work on the primary alignment and not touch the secondary anymore, right? *** I answered my own question... it does not. It only moves the green circle relative to the large black circle on the outside. *** |
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| Alrighty, here's me hoping this is good enough... |
