Someone else with collimation woes (with photos)

[mitchelln]

You don't need any paper. The idea is to replicate the normal light path. The laser just happens to provide a really bright source, enough to produce an image of the donut. Just bung the laser collimator into the Barlow and stick it in the focuser

[michaeldurban]

this is interesting.

I have the 250p (flextube).

When I centre my secondary and tilt it I cannot see the six mirror clips.

I have tried to tighten the primary screws and then genlty release them.

But for some odd reason I cannot see the clips..no matter what.

I checked my secondary mirror size (63mm) and that seems to be correct.

My collimation is perfect though...no problems with that..

Without hijacking this thread..anyone any ideas??

[michaeldurban]

on a second note...when I take out the cheshire and just look through the

focuser tube I really have to press my eye against the tube to see the clips.

so with the cheshire, it doesn't matter if the focuser is racked in

or not...the clips are not visible.

[mashedpotatomountain]

i found that too michael - to get round it i made a collimation cap to use instead whilst centering the primary clips -

if you do this & rack the focuser in fully, you should just about be able to see them.

rich

[wolfpaw]

on a second note...when I take out the cheshire and just look through the

focuser tube I really have to press my eye against the tube to see the clips.

so with the cheshire, it doesn't matter if the focuser is racked in

or not...the clips are not visible.

Make sure the focuser is all the way in and use a collimating cap. Unlike the 200P, it's really difficult/impossble to see the mirror clips in the 250PX using just a Cheshire!

[michaeldurban]

yes..i tried that, racking in the focuser...didn't show any clips..

even when i remove the cheshire and rack in the focuser and use

my eye, i still have to move my eye around a bit to see all the mirror clips..

[michaeldurban]

will try the colli cap...but the cheshire should give me the

correct centering of the secondary.\

for the tilt i use the cheshire and the center spot as a mark

[mashedpotatomountain]

will try the colli cap...but the cheshire should give me the

correct centering of the secondary.\

for the tilt i use the cheshire and the center spot as a mark

i think cheshires just show a slightly narrower FOV than a collimation cap that's all.

i use a cheshire too, but also double check with the colli cap to make sure i've got all the clips in view.

[michaeldurban]

well..I did my half-yearly secondary collimation...

The pic didn't come out that well but it gives an indication.

-centering the secondary (with the spider)

-up-down movement of secondary

- tilt of secondary

-(adjusting primary)

I used a clip on light...and shone the light onto the 45 degr angle plate  in

the cheshire..

cheshire inserted (see peephole)

still not 'perfect'..but perfect enough..

[wookie1965]

well..I did my half-yearly secondary collimation...

The pic didn't come out that well but it gives an indication.

-centering the secondary (with the spider)

-up-down movement of secondary

- tilt of secondary

-(adjusting primary)

I used a clip on light...and shone the light onto the 45 degr angle plate  in

the cheshire..

colliA2.jpg

cheshire inserted (see peephole)

colliA3.jpg

still not 'perfect'..but perfect enough..

That looks almost perfect i doubt you could get it any better maybe a tad but it looks spot on to me the secondary looks central and round and that's the hard part no need touch that again now unless to drop or bang the OTA just a tweak of the Primary.

[michaeldurban]

and..for that comment I will place a  'Like This' on your list Wookie..

(it's true...I was fishing for a compliment..)

[RichM63]

I'm wondering how bad is this secondary collimation? SW 200P OTA.

Ignore the dark band on the yellow card it's just a crease.

I've measured the pixels at the N, E, S, and W points from the secondary outer edge to the focuser edge and have the following values in pixels. (using the measure tool in Gimp).

N = 235.0

S = 277.0

E = 252.0

W = 259.0

I think that the secondary is too high when I look at it down the focuser tube it is visbly higher to my eyes.

The N to S difference seems too great.

The W to E difference is not so great.

Should I be attempting to correct this secondary.

For a better view use your zoom function. This is only at 33% for posting.

Any advice, much appreciated,

Richard

[F1Bird]

Wish mine looked like that!

[wookie1965]

I'm wondering how bad is this secondary collimation? SW 200P OTA.

Ignore the dark band on the yellow card it's just a crease.

I've measured the pixels at the N, E, S, and W points from the secondary outer edge to the focuser edge and have the following values in pixels. (using the measure tool in Gimp).

N = 235.0

S = 277.0

E = 252.0

W = 259.0

I think that the secondary is too high when I look at it down the focuser tube it is visbly higher to my eyes.

The N to S difference seems too great.

The W to E difference is not so great.

Should I be attempting to correct this secondary.

For a better view use your zoom function. This is only at 33% for posting.

Any advice, much appreciated,

Richard

IMGP1383_1.JPG

Check your spider for the north south but the mirror does need going a touch further into the OTA, this and a further tweak may make everything ok.

[RichM63]

Thanks 'wookie', I have adjusted the spider, and tweaked a little more.

This picture with an overlay of "Als collimation aid" I think that I'm pretty close.

N = 61.00

S = 63.00

E = 62.00

W = 63.00

Not sure if I need to be any tighter.

Cheers,

Rich

[michaeldurban]

yup...agree with Wookie....

East west movement is what you achieve via turning the 'middle' screw (crosshead/philips) of the secondary holder..

then adjust the circular appearance of the secondary..by hand (gently) rotating..

until it appears round whilst looking through your focuser...

and  -when north south- are not equal, release and tense the spider screws. and just play a bit...

unscrew a millimeter on south and screw in a millimeter on north (if that's that's case)

then check your alignment again..it should have shifted very slightly...

don't worry...unscrew one spider-screw even more, and then tighten the opposite screw...a few turns..

see what happens..

When all is in alignment ...leave it...

When 'locking in' the secondary (ie you have found the perfect circular shape and want

to hold that shape permanently)

Don't put too much tension on the three grub screws, just let them touch ..

you will need fine adjustments for tilting the the secondary afterwards.

the last part is getting the reflection of your primary in your secondary,,,

by tilting the secondary (note: use Astrobabys guide!!!!)

when all is in place....tighten each (secondary) grub-screw until the head of each screw feels tight..if that makes sense..

only then move to your primary (the word which shall not be named) ..springs...and center the whole shebang

as a note...

And I have said this many times..

yes..a laser (barlow combo) is great for getting a pretty decent primary collimation..

but please...use a cheshire combo sight tube..

it has crosshairs and makes everything so much easier and accurate.

better yet...the cheshire will show you when your secondary is 'round' in the tube, it will

tilt your secondary for the reflection and it will collimate your primary..

all of that without the introduced errors of using a laser collimator !!!!

pant pant...

I need a rest..

and a cigarette

(oh..don't go overboard...when you start measuring the north/south/east/west and then adjust these

coordinates because they are 'a millimeter out'.... just leave it please....)

[RichM63]

Yup that's exactly what I did Michael.

I don't have a laser, just a film cap with a hole, a short cheshire, 2 bits of card and a point and shoot.

"Als collimation aid" is well worth a download for anyone opting for this method on the secondary, as it allows resizing the 3 rings to suite your kit and check your alignement and circularity on the secondary view.

Best,

Richard

[michaeldurban]

A Caution on collimation..!!

I was in therapy for three months due to the well known astronomical disease :

OCC(S) -Southern Hemisphere strain OCC-V101-

(obsessive compulsive collimation syndrome)

After many sessions, my wife   -eh...who happened to be my councilor-   advised me to 'go to the pub for

crying out loud, like normal men do !!'

I took her medicine with a beer and was merry..

everyone lived happily ever after..

[wookie1965]

That looks spot on now don't think you could get it any better the hard part is done. You will not have to adjust your secondary again now unless you drop or bang your OTA just a minor tweak of your primary every now and then.

[mitchelln]

Als collimation aid is a really useful tool It's worth checking the proportion of area around the secondary remains constant as you wind the focuser in and out. The visible ring around the mirror will get bigger and smaller, but you should still see the same number of pixels NSEW. If not then your focuser is probably not square. Mine wasn't and it seems quite common.

[RichM63]

Evidently this horrible Winter weather has got to us, grown men/women talking about a missing pixel in N/S or E/W, is this normal.....???

However Mitch, I had done exactly that before posting my final results.

And yes, I did make physical adjustments to the focuser housing.

It's just a tweak to the West, a tweak to the East, a tweak to the North, and a tweak to the South.....

"Let's do the Colli--Mation again"

Took the 200P rig out last night, found a couple of unrelated problems, but the Collimation was spot on. Seriously chuffed because I had taken a punt on this one, but now I reckon this is better than it left the factory.

Now over to the 150P , which I know to be good, but I want to check using my newly found method.

The one important thing to be absorbed, is not to be frightened by a waaay off scope, providing it is not physically damaged, the rest can be worked out.

BTW I was worried about this 200P out of the blocks.

Cheers,

Rich

[wookie1965]

Like riding a bike now you should have no trouble with the 150p