Totally fed up now!!

[johnkirkpatrick]

Can't get the collimation of the secondary right at all. no mater what I do. Spent weeks playing with it.

Does anyone pass through Dumfries any time? If I was shown once I would be fine lol.

Head ache.....

[Digz]

A little far away for me lol, but what exactly is the problem?

Have you read through Astro Babys Guide to Collimation?

[tipftop]

hi john

could you post any pics of the probs you havin

dave

[kidlands]

John try youtube too. I find it better to see it done in the flesh, theres a few vids on there.

I think some are better than others but you can always cross reference it with the link Digz gave.

steve

steve

[johnkirkpatrick]

the problem is the dam secondary mirror and getting it centered and square to the focuser. I know what to to but just cant get it right. when I think i've done it I collimate the primary and get it out but the views are ok but no where near the views i was getting before.. I know its off and I know its the secondary causing the problem.. Ive studied AB guide, andys shot glass Youtube and the likes. and still just cant get to the point of being happy with it....

[GrantEb]

Have you tried using a "point and shoot" camera, or video cam centered in the eyepiece yet? It works wonders.

[Si W]

John, you could of been asked this before, but have you tried re-aligning your focuser and the center screw on your secondary.

[spaceboy]

the problem is the dam secondary mirror and getting it centered and square to the focuser. I know what to to but just cant get it right. when I think i've done it I collimate the primary and get it out but the views are ok but no where near the views i was getting before.. I know its off and I know its the secondary causing the problem.. Ive studied AB guide, andys shot glass Youtube and the likes. and still just cant get to the point of being happy with it....

I think it would pay you to have a look at the secondary in a new scope at a showroom. You may be surprised to find it's the same. If not, while you are there you could pick up a chesire collimator and ask for some advice.

[x6gas]

Ok. First thing is "Don't Panic!"

So long as you haven't unscrewed the secondary, 'polished' it with 60 grit sand paper and smashed it into the primary, everything is going to be fine!

Firstly, I'd really recommend blocking off the primary with paper and putting something coloured behind the secondary as described by Astros Baby. It helps a lot.

Then, with the telescope tube horizontal so that nothing can fall down to the primary you can wind in the adjuster screws a bit and then holding the secondary - but not by the mirror - slacken or tighten the central screw so that the secondary is pretty much directly below the eyepiece drawtube. Once you've got that you can use the three adjuster screws to get it exactly centred.

Remember that you might have to rotate the secondary to ensure that it presents a circle below the drawtube.

Follow Astros Baby's guide closely. If you don't have a Cheshire collimator then you can still get pretty good collimation with a simple colli cap.

As is said often, take your time and never over tighten screws. Other than that you can't do long term damage so long as you are careful not to touch the

mirror surfaces. IMHO collimating isn't as hard as it's sometimes made out to be!

[astromerlin]

Have you tried using a "point and shoot" camera, or video cam centered in the eyepiece yet? It works wonders.

This is the method I used after nearly 'giving up'. You just need a point and shoot preferably with a zoom function and center it with the focuser. Place a bit of coloured card behind the secondary so when you take the pic you will get the image of the dark focuser, the coloured card and the white secondary.

Using editing software, open the image and create a circle that is equal in diameter to the outer dark focuser and the inner white secondary. You can now move the circle (or create others) around the edges of the secondary mirror to see if it fits the same all round the secondary, if it does then the secondary should be in the right spot.

I couldn't get on with a chesire, could have been because the sighting hole was about 3mm in diameter and I just couldn't align my eye 'straight'.

I finish the primary collimation with the barlowed laser method.

[Doc]

I done a write up on collimating with a videocam I'll see if I can find it.

Have you actually tried your scope under the stars yet?

[Revs]

I assume you're using your laser collimator? Are you sure it is aligned correctly? Try turning it with the screws just loose enough and see if the beam wonders. Good luck buddy

[Doc]

Look at this thread:

http://stargazerslounge.com/equipment-discussion/99090-collimating-video-camera-tutorial-photos.html

[spaceboy]

Would I be correct in saying you have a crayford on your skyliner John? If you can perfectly center your secondary in the OTA with out distorting the tube by over tightening the spider thumb screws. You then center the secondary as recommended by AB as best as you can. If you find the secondary is tight to the top or bottom small adjustments can be made to the crayford by using the three adjusters around the focuser body. This is done in a similar way to aligning the primary mirror. If you take a close look you will see a hex key locking nut and a hex key dome nut. Simply loosen the lock nut and tighten the dome nut as needed. As with any screw do not over tighten. It may be a case of the focuser sitting flush and all the screws needing to be slackened of to allow adjustments to be made. There is only a small room for adjustments so this is going to be a pain to do and be patient. Once you have the secondary sitting Central in view you will need to go through the whole process AB explains to make sure everything is ready for final collimation.

[johnkirkpatrick]

Well that's it done ( woo hoo ) to a point am happy with. Not sure if its perfect but it's certainly a massive improvement. Thanks for the great video link ( a new one for me ) Steve. With that and AB's guide I got it done in no time at all. The hardest part was getting the Secondary to appear as a perfect circle under the focuser. Once I had that the rest just fell into place.

Thanks again, Now I can get back out and enjoy without convincing myself that my collimation as out...

[x6gas]

Result - well done!

[MikeD]

Nice one guy's, Karma will be smiling on you all for the next few days.

Mike.

[Si W]

Nice one guy's, Karma will be smiling on you all for the next few days.

Mike.

And Result in clear skies for all

[johnkirkpatrick]

Why does my collimation keep moving. My secondary looks fine? but I collimated my primary with my cheshire this morning as I noticed the centre ring and the cheshire hole had moved apart over night, then looked at it again tonight and they have moved again by a good few mm. Everything is nice and tight (not overly tight) and cant seem to get it to hold...

Note- the scope has sat still overnight so its not been nudged or bumped..

[Moonshane]

I find with my f5.3 scope the collimation of the primary needs tweaking every time I observe. As you move the scope around the sky the mirror does move a little in some (all?) designs. This is one reason some imagers collimate the scope several times per night and in the position of their next imaging target.

If you don't have them then get or make some tool free collimating knobs and maybe upgrade the springa. This will help with retention of collimation and ease of the task.

I find the push pull screws of the Skywatcher/Celestron designs a right pain having done a couple over the weekend.

[ken spencer]

Yes when I had the 8" DOB it was a pain to collimate because I had to use a Philips screw driver. When I got the 10" DOB it has knobs that can be turned very easily and therefore the operation is quicker and much easier to do. I collimate mine every time I go out and observe.

ken

[spaceboy]

Reflectors constantly loose collimation. OTA temperature changes cause flexing in the thin steel walls and the primary will also expand and contract slightly with warm and cold environments. weight of EP's and Position of the OTA perpendicular to the ground will also flex the tube slightly. Putting on and removing the dust cap, accidental knocks, too tight or too loose lock nuts etc, etc, etc all culminate to produce that small amount needed to knock collimation out by 1-2mm. It is recommended that collimation be carried out only when the OTA has cooled to out door temperatures and the OTA has been correctly balanced. Even when this is all done you will find depending on where the OTA is pointing and what EP you are using a slight error will occur. This slight amount should not cause any image degration for visual observing. You are more likely to find seeing conditions cause you more problems than a slight error in collimation during a session but it pays to check the collimation during a night out as sometimes the out side temperature drops quicker than the OTA temperature and this will also again have a "slight effect". I think this issue of flexing and OTA wall temperatures are being addressed by using Carbon fiber instead of cheap cold rolled steel. A good idea is to get a set of Bob Knob's SkyWatcher Dob to speed up collimation while out in the field and also elevate some of the risk of dropping Allen keys down the OTA in to the primary.