Collimation

[Sparta]

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

[wulfrun]

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

[wookie1965]

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

[wookie1965]

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

[Sparta]

Any better?

[Sparta]

Does the secondary need adjusting as well? I'm very nervous to get it right lol

[Pixies]

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.

[wookie1965]

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. 

[Sparta]

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?

 

[Spile]

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/

[Sparta]

Ok, took another photo of it pointing at a white wall

[cajen2]

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

[cajen2]

But Spile is right, a camera view may not be perfect.

[Peter Drew]

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.   🙂  

[Sparta]

Thanks Peter I'll try that!

[Sparta]

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.

[bosun21]

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 

 

 

 

[Sparta]

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?

[Sparta]

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.

[wookie1965]

If the central screw is tight you will have to back off slightly the three collimation screws usual 2mm allen head bolts 

[Spile]

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.