How is this collimation?

[Craig a]

After reading a topic in the imaging tips and tricks about using a phone with an adapter to collimate I had a go at it myself, this is my skywatcher f4 newt after I did it, now I’ve always had issues collimating it as each time I take the Cheshire out and reinsert it it’s always different so I had ago with the phone, how does the collimation look to all you experienced collimators? I know the real test is under the stars but the weather has taken a turn for the worse in Uk now so not sure when I can test it, does this look good, ok or poor?

[Pixies]

Here it is with Mire de Collimation:

Hard to be certain, as one can't see the edge of the drawtube in focus. But the secondary and primary appear to be well aligned.

2 things I notice:

1) The secondary doesn't appear to be exactly rotated towards the focuser. The offset (on the right) appears to be a bit high.

2) Have you double-checked that the secondary holder is exactly centered in the tube? The  vanes in the image aren't parallel with the Mire de Collimation reticle.

[AstroNebulee]

4 minutes ago, Pixies said:

Here it is with Mire de Collimation:

Hard to be certain, as one can't see the edge of the drawtube in focus. But the secondary and primary appear to be well aligned.

2 things I notice:

1) The secondary doesn't appear to be exactly rotated towards the focuser. The offset (on the right) appears to be a bit high.

2) Have you double-checked that the secondary holder is exactly centered in the tube? The  vanes in the image aren't parallel with the Mire de Collimation reticle.

Hi 

As pixies says it looks pretty well aligned and the secondary vanes could come over a smidgen, but don't think this would correct the offset much, I have a skywatcher explorer 150p on the secondary is offset a bit for some reason that escapes me, something to do with the focal length and fast scope, can't remember, also my old astromaster 130eq the secondary was offset aswell, all in all looks well alligned. You can always make a star test with an led light cover it in foil and make a pin prick hole in it to mimic a star, then place it as far away as possible and focus your scope on it, then slowly pull out of focus to check, I know this is possible on a maksutov and worked on my skymax 127. 

[Pixies]

When I mention the offset, I was talking about the apparent rotation of the secondary. It's the shape of the offset that indicates the rotation.

To my eyes, the offset appears to be in the direction of the blue arrow below:

The crosses show the intersection of the secondary image and the reticle circle. The offset should be directly inline with the focuser and when it is, the secondary will be directly aligned with the eye.

I'd say you need to turn the secondary about 5-10 degrees. Again - it's not much in the grand scheme of things. 

 

 

[Geoff Barnes]

11 hours ago, Craig a said:

does this look good, ok or poor?

Hi Craig, while it's not 100% spot on it is perfectly good enough for visual use. Would only need to be better for AP really.

[John]

17 minutes ago, Geoff Barnes said:

Hi Craig, while it's not 100% spot on it is perfectly good enough for visual use. Would only need to be better for AP really.

I agree. Get on an use the scope as soon as the clouds clear

[Craig a]

Thank you all for having a look at it, I only use this for imaging so would like to be better, I do believe that a fast Newtonians secondary would look shifted away from the focuser and my phone may not of been rotated enough to get the veins perfectly vertical and horizontally, yes i can see now the secondary needs rotating abit more so I shall go back to it have another go, the secondary an these scopes are a pain to get right! 

Edited August 18, 2020 by Craig a

[Craig a]

Also I did change the focuser to a moon lite and as a result to get the secondary centred in the focuser I had to move the secondary up towards the top of the tube abit 

[inFINNity Deck]

7 hours ago, Pixies said:

When I mention the offset, I was talking about the apparent rotation of the secondary. It's the shape of the offset that indicates the rotation.

To my eyes, the offset appears to be in the direction of the blue arrow below:

The crosses show the intersection of the secondary image and the reticle circle. The offset should be directly inline with the focuser and when it is, the secondary will be directly aligned with the eye.

I'd say you need to turn the secondary about 5-10 degrees. Again - it's not much in the grand scheme of things. 

 

 

I had this same 'issue' with my SkyWatcher 300PDS, so after collimation the secondary looked rotated. It was caused by the focuser not looking towards the centre of the tube, but being at an angle with it (as seen from the secondary mirror). The PDS focuser has push-pull adjustment screws that allows you to tilt it:

The whole problem with a skewed focuser is, that the central ray will not hit the secondary at the centre, but in order to get it at the centre of the primary, the secondary needs to be tilted. So although collimation looks good, it is not as the central ray as not parallel to the tube and thus not perpendicular to the optics. The difference are however small and perhaps not even noticeable.

This is what the focuser looked like after I had adjusted it for tilt, the adjustment is obvious (from the factory it was parallel):

I adjusted the focuser using a laser collimator. When looking from the front it is a matter of aligning the spider with the reflected image of the spider and then trying to split the laser beam on the secondary with it (this may be an iterative process, depending on the collimation error in the primary mirror). After this was done the rest of collimation was done as usual and the secondary came in line with the focuser.

HTH

Nicolàs

 

[Craig a]

46 minutes ago, inFINNity Deck said:

I had this same 'issue' with my SkyWatcher 300PDS, so after collimation the secondary looked rotated. It was caused by the focuser not looking towards the centre of the tube, but being at an angle with it (as seen from the secondary mirror). The PDS focuser has push-pull adjustment screws that allows you to tilt it:

The whole problem with a skewed focuser is, that the central ray will not hit the secondary at the centre, but in order to get it at the centre of the primary, the secondary needs to be tilted. So although collimation looks good, it is not as the central ray as not parallel to the tube and thus not perpendicular to the optics. The difference are however small and perhaps not even noticeable.

This is what the focuser looked like after I had adjusted it for tilt, the adjustment is obvious (from the factory it was parallel):

I adjusted the focuser using a laser collimator. When looking from the front it is a matter of aligning the spider with the reflected image of the spider and then trying to split the laser beam on the secondary with it (this may be an iterative process, depending on the collimation error in the primary mirror). After this was done the rest of collimation was done as usual and the secondary came in line with the focuser.

HTH

Nicolàs

 

When I fitted the moonlight focuser I did mark the center point opposite the focuser and adjusted the focuser to point at the Mark opposite 

[Craig a]

Ok I had another go at this after work, does this secondary look any better this time folks?

[Pixies]

Hi.

It looks quite similar to me. 

Did you manage to check how central the secondary holder is to the tube? Those vanes still look a wee bit wonky. I use a plastic set-square from one of the kids maths sets to check the distance from the centre screwhead to the tube inside edge where the vanes connect.

How are you checking the alignment of the secondary under the focuser? Are you using a sight-tube/cheshire?

[Craig a]

After I posted the latest update picture, I checked the veins and yes they were wonky I have now centralised them , to be honest I started from scratch again after this pic of it, will post up another pic of it tomorrow now I’ve sorted them wonky veins I’ve been at it for hours tonight and had enough 😂, will come back to it tomorrow with a fresh head and eyes