Collimating Skywatcher 150

[Altomar718]

Hi All

This may sound daft, but what are the signs that a scope needs collimating - Is it a blurred image?

I try to do a bit of photography and the image seems to be out of focus no matter how acreful I am focusing using the on screen image. When I process through Registax, it is always a bit out of focus and I wondered if the scope may need collimation as I have never done it !!

[jimmyjamjoejoe]

Blurred image, irregular field illumination, there are lots of signs, but i'd definitely check it if the images are blurry.

[Naemeth]

Hi All

This may sound daft, but what are the signs that a scope needs collimating - Is it a blurred image?

I try to do a bit of photography and the image seems to be out of focus no matter how acreful I am focusing using the on screen image. When I process through Registax, it is always a bit out of focus and I wondered if the scope may need collimation as I have never done it !!

Assuming it's a reflector, it will probably be out of collimation. If it's a refractor, it probably won't be unless you've dropped it, refractors don't lose collimation easily and are pretty difficult to collimate yourself.

It could be thermal issues too, or seeing issues if you are imaging at very high magnification.

[AndyWB]

Would it be worth posting up one of the blurred images?

[Altomar718]

Hi Andy - This is after going through Registax but NO wavelet adjustment. I know the image is small but I have ordered a larger barlow to try and improve that but like I said in the first posting, I wonder if the poor image is due to collimation ??

[umadog]

It's impossible to tell from an image like that if your scope is out of alignment. Blur could be due poor seeing or poor tracking or bad optics or bad collimation. An image like that can't tell you what it is.

Chances are that if you're asking if the scope needs collimating then it does. Buy a Cheshire combination tool and learn how to use it. That will tell what is out of alignment and how to fix it. Confirm with a star test to make sure everything you've done is right and that your centre spot is well positioned. If the sight-tube and Cheshire readings look right but the star test is wrong then your centre spot is probably not centred.

[Moonshane]

I collimate my scopes every time I observe and that's for visual. For imaging it's even more critical as you are using much higher powers. it takes a lot less time to collimate than to run and process a minute of footage.

[dcwales2012]

Likewise. I collimate my SW Explorer 150p everytime its moved. Surprising sometimes how far it's out of the donut just by taking OTA on / off mount.

I would say the image is a fair representation of what I would expect from a 150p in reasonable dark skies.

[Macavity]

Probably best to "star test" it. Defocus a bright star and check whether the "rings" are symmetricial / concentric.

There are quite a few articles devoted to the details of this issue. Nearest and most immediate, example:

http://stargazerslou...eflector-150f9/

[Altomar718]

Thanks a lot for the answers and as always, I appreciate you taking the time to help. I have bought a laser collimator, and it did need adjustion bt I dont know if it has impromed anything as we have had torrential rain instead of clear skies !!

[AndyWB]

At least it's not snow...! Presumably, you could test it by looking out a window at a far away tree or similar?

[Altomar718]

Thanks for the advice, bought a laser collimator and it was out of bonk ........ now got it pretty well bang on so whaen the thick cloud clears !!

[dcwales2012]

Hi, Just a suggestion. Have you checked to see if Laser collimator is collimated. I had one which would draw a 6" inch circle when rotated in EP twist-lock. So it looked centred but was way out. Sent it back as asked for replacement. Might be worth checking.

Regards.

[Bill57]

Hi, Just a suggestion. Have you checked to see if Laser collimator is collimated. I had one which would draw a 6" inch circle when rotated in EP twist-lock. So it looked centred but was way out. Sent it back as asked for replacement. Might be worth checking.

Regards.

+1 Never assume the Laser is collimated. I also have a Cheshire collimator which is easy to use once you've tried it a few times.

[Moonshane]

personally if I had a laser, I'd collimate the secondary with a collimation cap/sight tube/cheshire and then collimate the primary using the laser in a barlow. it's easy and accurate no matter how much slop you have in the focuser.

generally when collimating, always try to standardise the setup. e.g. have the thumbscrews oriented the same way each time you collimate and observe and also if you have more than one thumbscrew tighten them in the same way when you collimate and observe. I have a Baader steeltrack focuser which is very good but the three thumbscrews make the collimation tool move in different directions so you'd end up with a slightly different result each time.

collimation is a matter of do it well but do your best. inevitably issues when observing will affect how the collimation is maintained; e.g. tube flex with long tubes/heavy eyepieces, flexing of the thin tube round the focuser, slight shifting of the primary. these are unlikely to be seen at the eyepiece (but may be for imaging) so don't worry, just enjoy.

[Gomtuu]

if I had a laser, I'd collimate the secondary with a collimation cap/sight tube/cheshire and then collimate the primary using the laser in a barlow. it's easy and accurate no matter how much slop you have in the focuser.

Exactly what I do. Collimation cap (just drill a tiny hole through a dust cap) to centre the secondary, followed by cheshire and barlowed laser for the primary.