Collimating SCT.

[Mac]

Over previous years, i have spent more then my fair share of nights trying to get the collimation of my meade spot on.
Most nights i have had some success, but i then decided to go down the laser route.
After looking around for weeks I finally ordered an sct laser colminator (its now free to a good home).

After the said tool arived, i got to work getting the mirror aligned.
After spending about an hour I finally got the mirror collimated, as per the instructions.

On the night in question I found out that the scope was so far out of collimation, I had to start over

So i looked in to other ways of collimating the scope.
And came across various ways and means, but most of them were using the inter and outer focus rings.
Which is what i had been using anyway.

One web site started to mention about using the airy Disk as the final part of the collimation process.
so i decided to look in to this. Then i found out about using an artificial star to aid in the collimation process
Using either a 50 micron drilled hole, and another using a fibre optic.

Both of which were a tad expensive for what they were.

So i decided to make my own!

I ordered some 5mm Borate silica glass off of E-bay, and set to work on making my own star.
Hey presto, it only worked 1st attempt.


I know the picture is not great but will give you some idea of scale.
Drill bit is 1mm in diameter.
home made fibre 0.2mm ish as measured in photoshop.
the only bit that annoyed me was i broke off another 2 inches, which was probably about 5-10 times thinner again.
So im going to have another go and make another one,
Then to put it to the test.

However.......

This fibre 0.2mm when used with my scope at a distance of 20m (40 if i use a mirror and reflect around the garden)

will subtend an angle of 1 arc second.
Hopefuly I should be able to get the collimation of my scope spot on.
As i wont have any atmospheric distortions

Ill let you know how i get on collimating.

[JohnP]

cool - if it works can I borrow it to collimate my MN...

Good job,  John

[Mike]

I'd be interested to know how you get on with this as most artificial star techniques require the 'star' to be a considerable distance away from the scope.

[Fay]

Well done Mac!

[Mac]

If it works you can borrow it,

As for the distance, i know that might be a problem, but the minimum distance my Meade will focus down to is about 50ft,
and the furthest point i can get from it is about 65ft,
so its going to be tight, however i can always place a mirror at the back of the garden and double the effective length to 120 ft.

Just trying to find my ultra bright LED's, dont fancy looking down the scope at a laser.

[RobertM]

You can do a pretty accurate SCT collimation job indoors in 20 minutes or so and only one another helping hand required.  Last time I did it and checked against a star it was well nigh spot on too.

Basically the process is to sit about 8-10 feet away in front of the scope, look with one eye at the centre and try and make all the secondary rings concentric in the primary with the collimation bolts (that's where the helping had comes in).  You may be surprised but the accuracy needed to get them concentric is much less than 1/16th turn.  It's always best to check with a point source like a star afterwards as you don't use the scope horizontally but I've always found the results very good.  If short of a helping hand then I setup a mirror and look at the reflection of the secondary while adjusting the bolts.  The main reason I do it this way is that there are very few nights where I can see the airy disc and concentric rings and there's nothing a decent distance away that I can use as a point source.

Warning - you may see concentric rings for a short while afterwards but they soon wear off

[Mac]

Collimation of My Meade 10" Update.

Well kicking around the garden i remembered my meade just sitting there, so i decided to have a go at collimating it.

After removing the bird poo from inside!!!

Must have managed to get in somehow,
I decided to use the following,

set up in my bedroom and using CCd colimator, i set about collimating it

After about 10 mins the results i was getting were poor to say the least,
every new image would show the collimation off in some sort of random direction,

So i dug out the artificial star and set that up in the bedroom, and then used the defocused image to align the rings produced,
After about 25 mins of using the H9 as a live feed and tweeking the screws i managed to get the collimation as folllows.



Checking the circles with photoshop i would say they are spot on.

No flats 
The bunnies are on the front of the optics.

[RobertM]

Mac,

That looks very good, you should finish it off at high power just out of focus.  I did the C9.25 a couple of days ago and after a bit of jiggery pokery, got the same result.  The Baader laser collimator I originally used mucked it up a treat and was so far out that I couldn't even get proper focus on the moon.  I would have expected the Baader unit to be good but it ended up being less than useless and is going back!  As you say artificial stars are quite easy to make, in my case an LED torch and a piece of black card with a tiny fine needle hole was much better and cheaper.

That was real Poo in that scope? that stuff is really acidic and sticks like glue. Hope you got it all off!

Robert

[MarkS]

Nice one Mac - that's a great image of the de-focused point source.

Mark

[JohnP]

Looks good Mac - You should be all set for some great images now - collimated scope, new camera, guiding and pier... Looking forward to seeing some images.

John

[Mac]

collimated scope, new camera, guiding and pier

.

well thats a sore point at the moment,
Havent got guiding yet, but im still getting these weird and wonderfull images, and it's doing my head in.
(Havent got the image as i deleted it)

Tried last night to image the horse head,
Now i know that my polar alignment was nearly spot on, using a 15mm eyepeice the star drifted 1/4 of the view over a period of about an hour.
So over a period of 3 mins it shouldn't have been too bad.


but the scope is still shifting!!! or the camera is shifting!, something is not quite working and i've yet to suss it out,
I might have another play today in daylight to see if i can workout why it keep shifting,

Might strip the bearings down and give them a good service and regrease, see if that changes anything.

whilst imaging Alnitak for only 3 mins the final image had 4 images of the star!
So the camera/filter/telescope combination had shifted 4 times in 3 mins.

But the movement was in both RA & Dec, i could understand if the image had shifted in RA, as this would indicate that the worm gear was jamming / sticking,
but as for the Dec movement? There should be no movement in dec at all, as you only track in RA.

Going to think about this one. Will probably initilize the lx200 and get rid of any PEC training and start from scratch, that way i can eliminate everything.
and start by adding on by one, retraining the sensors, backlash, pec, ect.

By then i was cold and tired, so i packed everything away.

ps. i did also make sure there were no vibrations, as i set a dely of 1 min before i started, so i could go in and get a cuppa.

[Ian]

definitely sounds like the mount is doing something itself. Hopefully re-initialising the controller will help. I know I had fun with mine when the grub screws were a little loose on the drive pinions which made for erratic alignment and then tracking went off because the scope wasn't pointing where the controller though it was. Is there a way with your controller to see the alignment data? On mine, I can get info out of the controller such as polar alignment error and other parameters such as orthogonality and so on.

Does the controller have backlash compensation on? That has caused me issues in the past too.

Also, it's tracking at sidereal rate, not lunar I assume (not that that alone would account for dec drift).

[The Thing]

Hi Mac,

I have had all these problems and more - last time out I did the calibrate motors, train drives (I strap a green laser to the top and do it in daylight - just get the spot back to the corner of the chimney 5 houses away), update PEC. I tend to leave the backlash compensation on the default 10% having tried other values. Then everything seemed to sort itself out as long as I didn't change the target. I think that on my LX90 the worm gear mounting blocks are a bit loose as there is a definite clunk when you nudge the OTA with the clutches locked down. It shouldn't be though as Telescope House virtually rebuilt it a couple of months ago (maybe therein lies the cause:-{ ) Maybe something you should check?

As for SCT collimation - I've got that cracked. Here is a description I put together:
http://www.decorateandplaster.co.uk/astronomy/collimation_mask.pdf

[Mike]

Have you ruled out mirror shift?

[Rocket Pooch]

Mac,

Did you use a fibre optic lamp?  If so thats a brilliant idea, have to get one.

Chris