Sparta Posted January 28, 2022 Share Posted January 28, 2022 (edited) Hi all, complete beginner here looking for some confirmation on my new dob 8inch telescope being in collimation, here are some pics from what I can see through a collimation cap, I've adjusted the primary mirrors slightly to hopefully get it done. Edited January 28, 2022 by Sparta No pic attached Link to comment Share on other sites More sharing options...
wulfrun Posted January 28, 2022 Share Posted January 28, 2022 (edited) This is the guide I've used, no frills and no excess: https://garyseronik.com/a-beginners-guide-to-collimation/ EDIT: If you attached pics, they aren't showing up Edited January 28, 2022 by wulfrun Link to comment Share on other sites More sharing options...
wookie1965 Posted January 28, 2022 Share Posted January 28, 2022 (edited) The black dot needs to be dead centre its a tad out just adjust your primary a bit. I recommend a Cheshire/ Sight tube. On a second close up look it looks like the secondary needs moving just a bit down the tube. Edited January 28, 2022 by wookie1965 Link to comment Share on other sites More sharing options...
wookie1965 Posted January 28, 2022 Share Posted January 28, 2022 (edited) Needs to be a circle within a circle. In this picture you can see the black dot is a tad out. Edited January 28, 2022 by wookie1965 Link to comment Share on other sites More sharing options...
Sparta Posted January 28, 2022 Author Share Posted January 28, 2022 Any better? Link to comment Share on other sites More sharing options...
Sparta Posted January 28, 2022 Author Share Posted January 28, 2022 Does the secondary need adjusting as well? I'm very nervous to get it right lol Link to comment Share on other sites More sharing options...
Pixies Posted January 28, 2022 Share Posted January 28, 2022 HI Sparta! Welcome to SGL. Can you point the scope at a plain white/pale wall rather than that foil? It makes it hard to see what's going on? Cheers. 1 Link to comment Share on other sites More sharing options...
wookie1965 Posted January 28, 2022 Share Posted January 28, 2022 1 hour ago, Sparta said: Any better? The dot is dead centre now and I think the secondary looks like it does need moving but as said point it at a white wall. Link to comment Share on other sites More sharing options...
Sparta Posted January 28, 2022 Author Share Posted January 28, 2022 Thanks for the replies, I was hoping I didn't have to interfere with the secondary mirror, cos like I said, I am I complete novice to this, so if I understand right, does it need moving to align it with the primary mirror? Link to comment Share on other sites More sharing options...
Spile Posted January 28, 2022 Share Posted January 28, 2022 I am wary about making an assessment from a camera shot as parallax errors can make a big difference to what you can see. When it comes to alignment of the secondary, I would recommend using a Cheshire eyepiece and sight tube combination tool. This will explain what you are looking for… https://astro.catshill.com/collimation-guide/ Link to comment Share on other sites More sharing options...
Sparta Posted January 28, 2022 Author Share Posted January 28, 2022 Ok, took another photo of it pointing at a white wall Link to comment Share on other sites More sharing options...
cajen2 Posted January 28, 2022 Share Posted January 28, 2022 (edited) It does rather look as if the secondary is a little off to the right. I'd bite the bullet, tweak the secondary and then the primary. Edited January 28, 2022 by cajen2 Link to comment Share on other sites More sharing options...
cajen2 Posted January 28, 2022 Share Posted January 28, 2022 But Spile is right, a camera view may not be perfect. Link to comment Share on other sites More sharing options...
Peter Drew Posted January 28, 2022 Share Posted January 28, 2022 A couple of things look not quite right to me. The small black dot should be centered on the cross formed by the spider and the third mirror clip is not showing. Maybe a bit of a rotational tweak of the secondary and a final one of the primary will put it right. 🙂 Link to comment Share on other sites More sharing options...
Sparta Posted January 28, 2022 Author Share Posted January 28, 2022 Thanks Peter I'll try that! Link to comment Share on other sites More sharing options...
Sparta Posted January 29, 2022 Author Share Posted January 29, 2022 Ok took a photo during the day to maybe get a better picture, am I any closer? Can't seem to get the primary absolutely dead centre. Link to comment Share on other sites More sharing options...
bosun21 Posted January 29, 2022 Share Posted January 29, 2022 For this focal ratio the reflection of the cap Isn’t supposed to be in the centre. I ran into the same thing with my Stella Lyra Dobsonian 8”. See attached Link to comment Share on other sites More sharing options...
Sparta Posted January 29, 2022 Author Share Posted January 29, 2022 Adjusting the secondary mirror was always my worry, as I find then i try to adjust the centre screw, it's very locked in, and I'm afraid of breaking the spider veins as there is alot of tension, I noticed the same adjusting locks around the scope at the top of the primary, so they need to be unlocked before unscrewing the the secondary mirror? Link to comment Share on other sites More sharing options...
Sparta Posted January 29, 2022 Author Share Posted January 29, 2022 25 minutes ago, bosun21 said: For this focal ratio the reflection of the cap Isn’t supposed to be in the centre. I ran into the same thing with my Stella Lyra Dobsonian 8”. See attached Oh right, yes, I can see how I could make that mistake, I was thinking the the reflection of the cap and to be dead centre also, ok so I think an adjustment of the secondary should get me closer if needing so, the primary alignment part is not so hard, I just have a collimation cap to work with. Link to comment Share on other sites More sharing options...
wookie1965 Posted January 29, 2022 Share Posted January 29, 2022 If the central screw is tight you will have to back off slightly the three collimation screws usual 2mm allen head bolts 1 Link to comment Share on other sites More sharing options...
Spile Posted January 29, 2022 Share Posted January 29, 2022 The dark offset secondary reflection is “pointing “ at 4 o’clock and should be at 3 o’clock (explained in the link I posted above) but without the sight tube as a reference point it’s difficult to give a judgment. If your cap shows your primary is aligned (again explained in the guide) then I think you are good. Link to comment Share on other sites More sharing options...
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