Collimation help!

[RYan2040]

A very popular subject among novices such as myself so apologies!

As far as I can tell I have collimated my telescope pretty well (Newtonian Skywatcher 150p). However I just can't seem to get it right!  I have been to every website, PDF, tried tinkering with it a hundred times so I thought my only option is so ask people that know a thing or two! so here I am.  The main gist is my airy disc seems to look cental to me but when I am trying to focus on something (tonight was Vega and Saturn using 2x barlow and 10mm eyepiece), when I achieve what focus I can the star appears to look like lots of dots huddled together, only way I can describe it is it looks like a very condensed star cluster. Now since I have tried so many time I have convinced myself it must be something else, dirty eye pieces or mirrors perhaps?  Hope this makes sense and if anyone could maybe shed some light on my woes that would be great, thanks for taking your time to help a very frustrated man!

[Garethr]

Ryan.

Can you describe what steps you have taken to collominate and what you are using.

Gareth.

[brantuk]

Hi Ryan - welcome to SGL

When you remove all eyepieces and look in the focus tube - can you see your eye centered on the primary center spot? Can you see the three clips holding the primary in place? Does the secondary appear to be perfectly round (not oval at all).

Do you have a collimating cap? The airy disks are produced by focusing as best you can on a pinpoint star and then turning the focuser in or out a small amount - without a barlow. The airy disks produced either way should be central and concentric.

Not quite sure what you mean in your post - but those are a few basics to consider - if any one of those is not right then there is a misalignment in the mirrors somewhere. Hth

[BeanerSA]

What size eyepiece are you using when you get the fuzziness? I have the same scope, and get that same effect when I use my 6mm.

[Andy_E]

How long are you leaving your scope outside to cool for? sounds like it could simply a thermal problem. About half an hour should do it for a 6" newt.

[RYan2040]

Hi, thanks for all the replies.

I have noticed that when i look without any eyepieces i do have all three clips in view but when my eye is on the center mark the mirror/circle with my eye reflection in is slightly to the top and left of the circle that sits in ('m still confused as to what is reflecting of what mirror atm). So now i know it isn't properly collimated but i'm not sure as which bit to tinker to align it all. I hope this is making sense!

My scope came from flo and was crystal clear without touching a thing and i really hope to get it back that way, unfortunately someone knocked it over (the less said about that the better!) nothing was damaged but i've never been able to get it back the way it was and probably just made it worse!

Is it worth getting a collimation cap to help?

[laudropb]

What are you currently using ? I find a Cheshire the easiest way to achieve collimation.

[RYan2040]

I'm using a laser collimater, all be it quite a cheap one but it does seem to be calibrated when I tested it on a homemade v block. I was hoping for a miracle and get it done today as I'm currently sitting in a very sunny field in Kelling heath. I shall persist!

[acey]

Your issue has nothing to do with collimation. If the mirrors are not aligned properly then a slightly out-of focus star image at the centre of field will look stretched rather than circular. It won't look like a bunch of grapes. Ask yourself how an optical system can produce a multiple image. Not by tilting a mirror the wrong way.

There are various possibilities. One is that air turbulence is displacing the image very rapidly - this could give the appearance of a wobbly bunch of grapes, not a static one. If the grapes are stationary then there is a flaw in the system that is bringing light to multiple focal points. The possible culprits are the primary mirror, secondary, eyepiece, and your own eye. I would start with your own eye. if you normally wear spectacles, put them on when you look through the telescope. I have astigmatism, and when I view a point source without my spectacles I see a bunch of grapes. I don't wear my glasses while looking through my telescope, and I'm not troubled by the slight aberration this produces, but maybe your eyes are worse than mine, or you're more fussy (as can happen if you spend too much time collimating....).

If you eliminate your eye as the source of the problem, and the grapes are completely static, try rotating the eyepiece. If the grapes rotate then the problem is in the eyepiece. If the problem persists then I would suspect a defect of the primary mirror. Check that it isn't fastened too tightly in its cell, or under any kind of tension that could distort its shape.

If, on the other hand, the grapes are in constant motion, then stop worrying and wait for a better night with calmer air. And if in the end it turns out that your scope isn't perfect, don't worry about that either, because nothing is.