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SW 130p-ds collimation


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Hi,

 

I have just acquired the above scope to add to my collection, and have a question about collimation.

 

Historically, I've had no problem collimating my 200p OTA with my Cheshire, but this faster 130 (F/4.5 with the SW 0.9x coma corrector) might be a bit more challenging. With the brief break in the clouds (I mean, literally seconds) I've had to test the scope, the stars initially look misshapen, but I can't say yet for sure.

 

Would a laser collimator be worthwhile, or is the Cheshire good enough? I have removed and cleaned the secondary, as it was quite grubby (no stranger to this, as I've cleaned both mirrors on my Dob before). For what it's worth, collimation was miles out when I received it.

 

Here's how it looks ATM, after my Cheshire collimation.

 

large.20190730_004524.jpg.a9422b9962ec872cdee7399449812762.jpg

 

Any thoughts?

 

Anything else I ought to be looking at?

 

Cheers,

 

Kev

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Centre of primary looks off a tad to me secondary off set looks ok ? 

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Laser it is then, I guess.

 

They look simple enough to use, but my only concerns are about concentricity of the beam.

 

Then again, maybe I'm overthinking it.

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1 hour ago, 8472 said:

concentricity of the bea

Just spin in focuser slowly no need to worry if laser out just spin it around so it spins around polo ring if that makes sense 

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Yes, 

30 minutes ago, Bottletopburly said:

Just spin in focuser slowly no need to worry if laser out just spin it around so it spins around polo ring if that makes sense 

Yes, I was thinking along similar lines. 

 

I'll let you know how I get on.

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Kev, before you rush out and buy a laser etc, next time we are at a meet, have a go with mine.

You need a 2 inch focuser though....does the 130 have one ? I assume it does...?

 

In my experience misshapen stars are more likely cooldown and seeing related than collimation.

My scope is an F4 and i've found it just as easy to collimate as i did with my previous F6.3 version.

 

My issue on my scope is the poor quality secondary holder and spider that isn't ideal to work with,

certainly if you have a case of OCD. (Obsessive Collimation Disorder ?)

 

Having said that it seems to hold it collimation reasonably well, with only minute adjustments required.

I've read lots into collimation, and even now struggle to understand the finer points of it.

I just went the easy way, and invested in a good laser and Blug.

But i do have a Cheshire as well, to set the secondary, though once done, pretty much stays in position.

 

If you've not read it 'Astrobabys' is one of the definative guides into collimation.

 

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

 

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23 hours ago, Bino-viewer said:

Kev, before you rush out and buy a laser etc, next time we are at a meet, have a go with mine.

You need a 2 inch focuser though....does the 130 have one ? I assume it does...?

 

In my experience misshapen stars are more likely cooldown and seeing related than collimation.

My scope is an F4 and i've found it just as easy to collimate as i did with my previous F6.3 version.

 

My issue on my scope is the poor quality secondary holder and spider that isn't ideal to work with,

certainly if you have a case of OCD. (Obsessive Collimation Disorder ?)

 

Having said that it seems to hold it collimation reasonably well, with only minute adjustments required.

I've read lots into collimation, and even now struggle to understand the finer points of it.

I just went the easy way, and invested in a good laser and Blug.

But i do have a Cheshire as well, to set the secondary, though once done, pretty much stays in position.

 

If you've not read it 'Astrobabys' is one of the definative guides into collimation.

 

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

 

Cheers, Rob

 

I've only just seen your post and I've only gone out and ordered one already, ah well - didn't cost the earth.

 

Ta for the link. I've done my 200p many a time, so I would have thought the smaller OTA shouldn't be all that different.

 

With the clear skies tonight, I got a longer run troubleshooting.

 

As I expected the optics are just not right (collimation is pretty good, by my standards), with weird triangular stars. Clearly not collimation, then.

 

large.1473701109_PinchedOptics.jpg.a46fe9e97ff7ad9f7e8c8b0fff797d1b.jpg

 

Bears all the hallmarks of pinched optics.

 

I loosened the 3 primary lock screws on the end of the OTA and instantly saw better star shapes, but still not perfect.

 

Next, I popped out the primary cell and it looks like a previous owner had tightened the 3 primary cell clips with as much torque as humanly possible (well not quite, but you get my drift), and hence distorting the mirror. ?

 

Clips now loosened to a more sensible level and mirror rotated 60 degrees or so, just for good measure. With about 10 seconds of star test evaluation before clouds drifted over, I think i may have sorted it.

 

With clearer skies, I'll know for sure with a more thorough test.

 

Cheers, All!

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Nice one.

Its amazing how sensitive these mirrors are to almost everything.

 

 

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It might take a short while for the glass to come back to proper shape, mine took a couple of weeks to settle down again. I did this to mine the first time I ever took a mirror out and I thought I had killed it until I received more sensible advice. 

Apparently you should be able to rotate the mirror under the clips, I use a couple of sheets of baking parchment as a feeler gauge, it won't scratch the mirror and allows just the right amount of movement.

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Great advice, Martyn - much appreciated.

 

I nipped the clips up so it just lightly held the mirror. I'll follow your recommendation, loosen the screws off and use the baking paper method.

 

Thanks to all involved.

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Just wondering......?

 

Is there any sort of alternative to mirror clips ?

I think they are a crude way of holding a mirror in place.

If the bloody things weren't there, they'd be no such thing as pinched optics would there ?

 

The clips on my OO scope are huge ugly things and are a considerable source of diffraction.

SCTs don't have them.....so why do us Newtonian users have to have them ??

 

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Yes, it's maybe not the best option, Rob.

 

I've popped the primary back out, cleaned it and the slightly loosened the retaining clips, as per Martyn's excellent baking paper advice.

 

Set the OTA back on my static tripod and pointed towards Polaris last night (as to minimise trailing), and now I get this...

 

large.Autosave.jpg.241c610a44e169c92dd520c31f225778.jpg

...and with Bahtinov mask:

large.Bahtinov.jpg.c9f2025c0e884863f358139136f134ef.jpg

 

No more triangles! ?

 

I know collimation isn't perfect, but I'll sort that later. I'm pretty chuffed it's all sorted now.

 

Thanks again, Martyn!

 

 

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All down to costs Rob.

There are other much better ways but the manufacturing cost would not make it practical for mass production.

Very rare any ATM will use clips.

Most use a sling or better still Whiffle tree posts with rollers.

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