collimation help in darkest Wales

[Ally8446]

Is there anyone out there that lives anywhere near Welshpool, Powys. No matter how hard I try I can't seem to get my secondary mirror central in the focus tube. I've followed Astro baby,s guide to the letter with no joy. Just wondering if someone could meet up with me to show me where I'm going wrong. Long shot I know. Fingers crossed. Clear skies. Al

[tsh]

I am not an expert, but I do have the same scope and noticed an old thread somewhere reporting similar issues.

I'm not sure if the goal of centring the secondary is valid for this (fast) scope. Certainly I notice that the reflection of the focus tube on mine indicates that it is not completely central. The whole of the primary is however visible. It's not helped by the spider being a single plastic moulding with very limited scope for rotating the secondary.

I skipped the primary alignment part on mine, and did what I could using a film canister and some aluminum tape as a reflector. Not yet sure if this has helped or not, waiting for drier weather...

[Russty]

Did you look at ABs pic of the offset "fast" newt collimated scope? Fast newts are slightly offset from central unlike the slower newts. This could be your problem.

[badgerchap]

I have an F4 and likewise, centering the secondary is awkward. However, it's so large I don't think it's an issue. I go near Welshpool pretty often (grew up in Manafon near Berriew), so next time I'm passing? Should be there over Easter?

[alanjgreen]

From your words, I assume you are stuck at the early stage of tying to get a "circle in a cirlce"?

I do this in 2 stages

1. Aim to get the secondary in the middle of the focuser by using the center screw (tighten pulls in up & loosen to push down the tube), do not worry about the shape of the secondary, just aim to get it in the center.

2. NEXT, I loosen all 3 allen screws, put my hand down the tube and grabbed the secondary plastic holder (not the lens itself), then as I contort myself to look down the focuser tube, I rotate the secondary until it becomes a "circle" in my view (as opposed to other more elongated shapes which mean that it needs rotating slightly)

Be sure to move it slowly and take your time

When you have a "circle" them tighten the 3 allen screws back up and you are ready to move to the next stage of MANY small adjustments to one of the 3 allen keys at a time for final alignment with the primary. At this final stage, you loosen 2 allen keys one sixth of a turn and tighten the other one one sixth of a turn - if it improves then keep the change - if it makes it worse then reverse the change and choose a different 2 to loosen.

two steps forward, one step back - if it all goes pear shape you may need to return back to earlier steps to get the "circle in a circle"

Just think to yourself "it can be done, but it may take some time!"

Alan

[Ally8446]

I have an F4 and likewise, centering the secondary is awkward. However, it's so large I don't think it's an issue. I go near Welshpool pretty often (grew up in Manafon near Berriew), so next time I'm passing? Should be there over Easter?

[Ally8446]

That would be great Badgerchap. Let me know nearer the time and hopefully we can sort something out. In the mean time I'll keep 'fiddling' : )

[Ally8446]

Thanks for all the replies guys, you really are a friendly and helpful bunch : )

[badgerchap]

Haha alright, fiddle away! I'll be in touch.

[DrRobin]

Hi,

I have a 10" F/4 newt and centered the secondary after removing it for cleaning using a webcam. I placed an unmodified webcam (I.E. lens in place) in the focus tube and to get an image of the focus tube and secondary. I then used Mire de Collimation to centre the two. I started with an Xbox camera and glued an old 1.25" barrel over the lens and body. It doesn't matter if it is not perfectly central as I aligned the secondary against the shadow of the focus tube.

I started by following Astro baby's guide (measuring the spider), but found the secondary impossible to re-centre by eye and ruler. I thought I was close but the camera and Mire de Collimation told me I was miles out. I then adjusted it on the camera until it was perfect.

After that I collimated as normal. At the end, the secondary looks central in the focus tube, but miles out to one side when looked from the primary, this is correct.

Robin

[badgerchap]

Thanks DrRobin, I'll be trying that myself.

[DrRobin]

Hi,

Yes give it a try, worked for me. I can't claim originality for the method, I saw it described somewhere, but can't remember where.

My Xbox camera was only a fiver and I used Sharpcap to view the images with Mire de Collimation as the overlay. I think somewhere there is a description of using M de C to collimate the whole scope, but I reckon if you have a laser, or Cheshire they will be faster and more accurate.

Collimation seems to be one of those daunting tasks and when it doesn't go right seems to sap you of your will to go on. I know, I was 2 months and several hundred pounds collimating my SCT and there is only the secondary to adjust on that. I made the final and most accurate collimation using a home made (less than £5) artificial star, wish I had tried that first.

My implementation of an artificial star is shown here

Robin

[MadAlbert]

Quite happy to help - I'm in Aberdovey!