Does this collimation look OK?

[edarter]

Title says it all really. I hate collimating and therefore rarely do it, which in turn means I'm not familiar with it when I do. Just spent a couple of hours doing this, on my 130pds. Does it look acceptable?

Thanks

Ed

[edarter]

just started an imaging run and I'm getting funny shaped stars. This may not be related to the above collimation though as I've never managed to nail down the spacing of my Baader MPC mk3 perfectly. WOuld be interested to hear what people think could be causing these:
 

[alacant]

20 hours ago, edarter said:

Does it look acceptable?

We can't tell because we don't know the orientation of the photo. One way of indicating this is to place your finger over the tube opening to coincide with the focuser side of the tube.

19 hours ago, edarter said:

could be causing these

All in the same direction getting worse to the left. I'd go for tilt. When you're certain the collimation is ok (use e.g. this guide), I'd look first at the cc attachment. Lose the M42 adapter and go for around 60mm from the m48 thread shoulder. Then the flexible stuff in the focuser, then the mirror cell, then ingress of the focuser barrel etc etc...

Don't overthink it though. It's easy to fix if you take it methodically, a step at a time.

Cheers and HTH

[rickwayne]

Suggestion: Download ASTAP and run a couple starfields through its image inspector. That will quantitate the problem, though it won't distinguish coma from tilt. I'm an Richey-Chrétien guy so I don't know much about collimating Newts.

[edarter]

On 08/02/2023 at 15:08, alacant said:

We can't tell because we don't know the orientation of the photo. One way of indicating this is to place your finger over the tube opening to coincide with the focuser side of the tube.

All in the same direction getting worse to the left. I'd go for tilt. When you're certain the collimation is ok (use e.g. this guide), I'd look first at the cc attachment. Lose the M42 adapter and go for around 60mm from the m48 thread shoulder. Then the flexible stuff in the focuser, then the mirror cell, then ingress of the focuser barrel etc etc...

Don't overthink it though. It's easy to fix if you take it methodically, a step at a time.

Cheers and HTH

ah ok, didn't realise that tube orientation was important for this. I'll another image with that in mind.
Thats exactly the guide I used  Took the opportunity to upgrade the secondary adjusters when I did it and move the primary up the tube a few mm so that the FT is not in the OTA much, which is now about 5mm at focus.
I don't use the M42, I went straight to M48 from the get-go but it is spaced about 55mm (with a shim after some experimenting previously to get star shapes ok-ish) 60mm seems a lot further than the Baader recommendation for spacing, will that work?? Happy to try it though.
Ref focusser - I've removed the rubber gromets and adjusted the tension on the teflon bush to bring the resistance back to what it was, so I would hope that this and the fact that I haven't cut the FT (and therefore its still on all the bearings) means there shouldn't be any tilt from that?! Racking in and out is certainly nice and smooth, but enough resistance that it supports the weight of the DSLR when vertical.

 

17 hours ago, rickwayne said:

Suggestion: Download ASTAP and run a couple starfields through its image inspector. That will quantitate the problem, though it won't distinguish coma from tilt. I'm an Richey-Chrétien guy so I don't know much about collimating Newts.

Thanks Rick, I'll do that also

Getting all sorts of issues with guiding lately which I'm also trying to fix. Treating that completely separately from this though as I suspect this one is going to be fairly easy to resolve. Dreading the thought of having to strip the mount and service it if thats what is needed for the guiding thing!

Ed

[alacant]

1 hour ago, edarter said:

60mm seems a lot further

Baader recommend 58mm. Our hands on experience is that that doesn't give corner to corner over aps-c. 

1 hour ago, edarter said:

haven't cut the FT (and therefore its still on all the bearings)

?

Unless you deliberately cut too much, it remains on its bearings, cut or not cut. 

[Spile]

On 07/02/2023 at 18:04, edarter said:

Title says it all really. I hate collimating and therefore rarely do it, which in turn means I'm not familiar with it when I do. Just spent a couple of hours doing this, on my 130pds. Does it look acceptable?

Thanks

Ed

 

It looks close to me, especially if the focuser is is a 8 o'clock? I'd place a piece of coloured paper behind the focus tube so that you can see the edge of the secondary. The green ring above is a guess on my part.