Collimating

[andreas.jordan]

Hello All,

I've been reading through the article here on "passive" collimating and am still confused about a few items in the article...

1. Do you need a sight tube?
2. Is a collimating 'cap' sufficient?
3. If using a laser collimator, do you still need the other gear? ie. cap and sight tube?

I see that Andrews Communications has the following Laser collimator for $59...is it any good?
http://i304.photobucket.com/albums/nn183/andy_2501/gs_collimator.jpg
Guan Sheng deluxe Newtonian laser collimator...A$59

At this point, I cannot determine whether its a collimation issue causing out of focus images or whether its an atmospheric affect or something temperature related.

Background Info:
I'm asking about collimation because although I got to see what I believe to have been Jupiter and four of its satellites, it was fairly low in the sky (so therefore more atmosphere to see thru) and was coming through all fuzzy.

[multiweb]

1_ it helps to initially position the secondary.
2_ a cheshire is needed yes. I assume you have a central spot on your primary?
3_ yes you do. Laser is good but you need to check visually as well.

The GSO's fine. I've got the same from Andrews. Make sure it's collimated too. Stick it on a lathe and project the red dot on a wall at 3m. Screw the hex heads until the dot stays stationary when spun.

Check your scope on a star with a barlowx2 and a 10mm eyepiece. Defocusing will show you concentric rings if collimation is alright other wise they'll be offset or your star shape will be odd.

[andreas.jordan]

Thanks Marc, although I don't actually own a barlow lens as yet. All I got with the scope was the 10mm, 25mm and a collimating cap.

[multiweb]

That should get you started. Pick up a cheshire for $25 or so. Once your secondary is aligned the rest is pretty straight forward. The star test is the icing on the cake. There are a number of colimation tuts for newtonians and others on these forums and online.

[orestis]

Hi Andreas,
I have a 5'' reflector and when it is collimated it can stay like that for about half a year or so.i see you have a 6'' so once collimated you wont have to worry for a while.
if you got a collimating cap use it, all i use is the dust cap with a tiny pin hole in it it works great.
If you want to get accurate results then get a chesire or better yet a laser collimater as visual collimation can be inacurate.
The bigger the scope the more you have to collimate it .

Orestis:thumbsup:
happy viewing;)

[erick]

Hi Andreas

It's getting a bit late in the year for Jupiter to check quality of view. You are right - by the time the sky is dark enough, it is now too low for best viewing. Go for the Moon when directly overhead (often during the month) or Saturn in a few months when it will be directly overhead in dark skies.

OK, there will be a lot of views and personal preferences - eg. some observers are very happy with what they can achieve by eye, looking down the focusser draw tube. Good luck to them! Here are my views for your 8" reflector.

I don't believe a collimating cap is sufficient or even needed.

A sight tube is good - to get the secondary mirror correctly located with respect to the focusser. It can also do a good job of checking that you have the secondary mirror tilt set fairly well.

A laser is good to get the secondary mirror tilt set fairly well - very easily. The laser you mention can do a good job, but hopefully the spot is not too big or mis-shapen, and it first needs checking that it is itself correctly aligned and then adjusted with its grub screws if needed. There was a recent DIY item on improving the mount of the internal laser module to improve the pointing/adjustment of these lasers - involving removing one internal o-ring.

A cheshire eyepiece (often comes combined with a sight tube) does a good job of getting the primary mirror tilt set fairly well.

A laser can do a reasonable job of getting the primary mirror tilt set, but is not most accurate unless you use a barlow lens with it and use the "barlowed laser" technique. You will probably make good use of a 2x or 3x barlow lens anyway, during your observing, until your completely fill your eyepiece case with every possible focal length!

There are more sophisticated tools, but you won't need them for visual observing with an 8" f6 reflector.

So, in summary, get a combined sight tube/cheshire eyepiece. That will get you into good collimation territory.

Alternatively, get a sight tube and a laser. That will get you into pretty good territory and good territory if you can add a barlow lens to your laser for the primary mirror tilt step.

Of course, you can always get much better collimation by "star testing" - depending on good enough seeing conditions to get a good star image to work with. Of course, we could then talk about having an "artificial star" to work with - but that is another story.....

[andreas.jordan]

Thanks all for the great advice. I'll begin with the collimating cap if only to get my head around the theory and in the meantime, check out the whats available locally in the way of collimation tools.

[RAJAH235]

Hi Andreas..
If you do the collimation as per the ^ good instructions then all should be fine.
For ref;...
> http://www.skyandtelescope.com/howto/diy/3306996.html
> http://www.skyandtelescope.com/howto/diy/3306876.html
If you start by checking if the 2ndary is centred in the focuser tube,
then the off-set should be very close.

Regs, L..

[andreas.jordan]

Alrighty then! I just placed my order with Andrews Communications for the following:-

1. Cheshire eyepiece - Cheshire design, long Newtonian type $49.00

2. Laser collimator - Deluxe Newtonian return beam type. Latest version. Has half-silvered 45° mirror target for easy primary mirror collimation. $59.00

3. [FONT=Arial]Barlow - 2.5x magnification, 1.25", fully multi-coated, 3 element apochromatic $49.00


...

and the Astronomy 2010 Night Sky Guide


I guess while I wait for the items to arrive I can re-read all those handy articles about collimating :P

[erick]

And you thought that once you'd bought your scope, expenditure was over :D

[andreas.jordan]

I know. Still tho, the family all have things they can buy me now for bdays, xmas, fathers day. Better a set of filters than underwear :heh:

[erick]

Better a set of filters (or, ummmm.... Naglers?) than underwear :D

[Gemini2544]

Hi Andreas I found this to be most helpful.

http://www.andysshotglass.com/Collimating.html (http://www.andysshotglass.com/Collimating.html)

I't's a short video lesson on doing a Collmination. Seeing it done makes easier with what you have read.

Good luck.