Newtonian Collimation

[Beagleboy]

Hey folks!

I'm still figuring out the basics of collimating Dobby, my 200p Newtonian. I'm using a Revelation 'Astro' laser collimator to do the job and the process seems straight forward enough. There's just one wee thing I'm not quite sure about. Once I've aligned my secondary and moved down to the primary mirror, I loosen off the locking 'hex' grub screws and adjust the mirror with the large slotted screws. However, without fail I seem to end up in a position where one of the adjustment screws is barely tight and the other two are nipped in pretty much as far as they'll go. Is this normal?

Once aligned....or what I think is aligned....I can still see that the stars at the edge of my 25mm eyepiece are streaked a wee bit. Is this indicative of my adjustments being way, way out?

Cheers for any advice.

 

C. 

[wookie1965]

I was told to screw the 3 primary screws all the way in then give them half a turn back then collimate,  as per your laser collimator I would check that as a lot of lasers need collimating,  unless you pay £100 for a howie glatter or a hotech better using Cheshire/sight tube. 

[todd8137]

Before you put the laser in could you see all three mirror clips (you may have four )  on the primary  ?  As wookie sugested  do that first and then check with a sight cap/ tibe to see if you can see all the clips that hold the primary in place ,if you can not see,all three clips a,ter thenscrews on the secondary till you can 

also google 

astrobabys guide to colamination 

pat

[Moonshane]

try this 

Does your primary mirror cell have springs? Usually the dob cells are push pull I think so you loosen two bolts and then tighten the hex grub to push it up if this makes sense.

[Beagleboy]

Actually, that does make a lot of sense Moonshane! So it's a bit like the balancing act I do when trying to adjust Shimano cup and cone hubs on a push bike.... tightening one up against the force of the other....which is why all my bikes now have cartridge bearings :-)  . Methinks I'll go home and have a play with it tonight, although I've already resigned myself to binning the laser collimator and shelling out for a Cheshire. I think you're onto something though, I'll let you know how I get on. Cheers!

C.

[Moonshane]

I prefer Cheshires myself.

[Owmuchonomy]

As above, lose the laser and choose a Cheshire. I did. 'Streaky Stars' at the edges of your view is normal for a Newtonian as long as the effect is even. Like the rest of us you will benefit from a coma corrector for that affliction.

[Beagleboy]

I had a play about again last night. There doesn't appear to be any springs that I can see on Dobby's (Skywatcher Skyliner 200p), primary mirror cell. I can also see the four clips holding the mirror in place when I look down the focusser without any eyepiece in place. Although I did give myself a wee bit of a Mordor style fright, until I realised it was my own bloodshot eyeball staring wildly back at me. As far as I can make out, the adjustment of the primary mirror is via three Philip's screws which 'push or pull' the mirror cell and three allen grub screws which then push onto the cell, 'holding' the adjustments in position. All that appears to lie between the Philips screw and the outside of the mirror cell is a wee rubber washer.

So anyway, it'll be the end of the month before the wife'll give me enough pocket money to buy a Cheshire  , so I kept on playing around with the Revelation 'Astro' laser collimator. Again, once I had the secondary neatly lined up, no matter what I did, I seem to end up with one adjustment screw nearly loose, and the other two tightened up almost as much as they'll go. Just seems a bit iffy to me, like something somewhere is seriously out of kilter and I'm having to go to the extremes of the adjustment range to compensate.

One last thing I did notice, and I don't know if it's indicative of anything, is that once I've set the adjustment so the laser point is disappearing back up its own...emitter, everything seems fine whilst the scope is tilted above the horizontal, but drop the scope down to horizontal and the laser point shifts. Is this just because of slop in my focus mechanism, dodgy cheapo laser collimator (even though every online review said it was the best thing ever  ), or something loose in me scope?

 

Cheers again!

C.

[spillage]

Make sure you colimate your lazer first.

If you have a block of wood and four large nails you can make a tester. Hammer in the nails to make a cradle out of two v's. Place the colimation tool into the v's and place this a good distance away from a flat surface and rotate it to see if the dot wobbles.

You should see three blobs of gunk that will be covering the small allen screws to adjust the lazer. Removing this to access the screws is the hardest part.

When I use mine I always make sure to place it so its facing the back of the scope. This allows for any discrepancies in movement and means I can align the primary whilst being able to see what going on at the same time.

 

cheers

spill