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Collimation fustration!!!

NIGHTBOY

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NIGHTBOY

NIGHTBOY

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Yes I see but as I stated before...

I can't get all 3 clips in to view nicely but when I do the reflection of the focuser is not on the centre like the above pic. When I adjust the 3 Allen bolts to get the focuser in the centre of view, one of the 3 clips go ou of view.

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mitchelln

mitchelln

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Once you get your secondary sorted I can highly recommend using a barlowed laser to align the primary. The barlow spreads the laser light much in the same way as normal light is passed. You get a laser light image of the primary's centre dot on the laser collimator's angled face. This method is much less susceptible to movement and position than just using the laser by itself.

Primary advantage over a Cheshire (we're talking for primary adjustment here) is you can see the dot image whilst you are adjusting the mirror screws. With the Cheshire you are working blind and end up hopping from one end of the scope to the other. Disadvantage is you can't do this in full daylight as the dot reflection is fainter than the raw laser spot.

I've checked with a Cheshire a few time after doing this and always found it to be spot on. Saves an awful lot of agro :)

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NIGHTBOY

NIGHTBOY

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Most confusing day of my life haha sure its the same for you trying to explain too!!!!

Here is exactly what's happening please read carefully...

First I loosen Allen bolts.

Then I hold the secondary mirror and adjust the screw until I can see all 3 clips that hold my primary mirror on.

At this point the reflection of the focuser is off centre.

I then turn the Allen bolts to brin the reflection of the focuser in to dead centre.

Now the focuser is dead central and one of the clips from the primary is out o view again.

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mitchelln

mitchelln

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It could be your focus tube is not square. It wasn't on my 300P and your problem sounds similar to what I was seeing. Does the view of the secondary change as you wind the focus in and out it's full travel? I would use a simple pin hole for this test as it gives a wider view than a sight tube. When my focus tube wasn't square I noticed the gap to the top left edge of my secondary was changing. The overall visible portion should remain constant even if the secondary itself is misaligned.

I wouldn't just wade in and adjust the focus tube alignment though until someone more knowledgeable than me comments!

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wookie1965

wookie1965

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The middle screw lines the secondary under your focuser look through your focuser without anything in or with cap with 1mm hole in you don`t want the crosshairs of your Cheshire confusing you make sure its in the middle and showing full circle. Use the 3 collimation screws to get the 3 clips in sight using your sight tube now (Cheshire) you have to fiddle with these turning one in and another out until you get it just right once you have done this your secondary is lined up. Now all you have to do is align your primary (easy bit) look through Cheshire and bring the black dot into the centre of the doughnut that`s you collimated.

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wookie1965

wookie1965

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The picture shows your focuser there is no reflection that sticking out is your focuser (arrowed)on post 44 and 61 i say use the middle screw to get the mirror lined up under the focuser tube and showing full circle, the collimation screws then will tilt the mirror to show the 3 primary mirror clips.

post-20428-0-49565900-1380035109_thumb.j

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AlexB67

AlexB67

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An again...

I am using the screw to get the focuser in the middle.

When I turn the Allen bolts the focuser goes out of the middle.

I've said this 10 times now...

Patience is a virtue :smiley: . Not read the  whole thread but  FWIW, the only tip I can give if it starts getting on you nerves, Go back to the beginning, be systematic and do it in the right order.  Secondary first, until you are sure you are happy, then primary, the latter is really easy, but the former  can be a bit frustrating because the secondary screws can be a bit fiddly to work with. Once you get close with the secondary, really work with small turns and tiny adjustments of the collimation screws.

I found this article good for the diagrams http://www.propermotion.com/jwreed/ATM/Collimate/Chesire.htm  without being overly lengthy.  Good luck.

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wookie1965

wookie1965

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Right, looks like my mistake ha. By saying 'The reflection of the focuser' I was referring to the largest black circle INSIDE of the reflection of the primary mirror..

What exactly is that??

That is the inside of your scope opposite your focuser. If you read the very first post i sent you the third link he puts coloured paper in it will become a hell of a lot clearer then.

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AlexB67

AlexB67

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I concur with Wookie here, the first thing to get clear is to understand what it is you are looking at, the technique of using a sheet of paper to block the reflections etc this will make that easier, as explained by this chap here from Orion telescopes, he uses a cap and not the combination tool, but it demonstrates what I mean where to place the paper.

http://www.youtube.com/watch?v=YAVGcGEBmCE

Stick at it and you'll get there. :)

edit: sorry Wookie already said it before me, but anyway, another source.

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NIGHTBOY

NIGHTBOY

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Ok now this is with everything loose and a piece of paper in the scope. No matter how I move the secondary mirror I cannot get the paper to be the same thickness all the way round the outside of the reflection of the primary mirror. There is always a black spot on the left hand side of it.

IMG_2128_zps71164000.jpg

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wookie1965

wookie1965

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the arrow is your secondary mirror the outer edge of it now position this in the middle of that circle around it making sure that the mirror does not present an oval but presents a full circle towards you. so you can see a gap the same width all the way around.

post-20428-0-16119800-1380038770_thumb.j

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AlexB67

AlexB67

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Also, If it helps at all, you should entirely ignore what you see in the secondary mirror reflection at this stage, as Wookie said , concentrate on your first goal only and adjust the secondary so it forms a concentric circle with an equal border around it, forget everything else 'till you get to that point.  Post another picture if you like when you think you got to that point best you can.

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Moonshane

Moonshane

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I am currently writing a guide to collimation which will be available within a week or so. Hopefully this will help you and others in due course. For now, I should stress that the basic steps are as follows

1) for now assume your vanes and focuser are square. they almost certainly are and there's capacity for enough adjustment usually within the primary secondary.

2) put the paper between the secondary and the primary so you cannot see the primary.

3) using the central bolt only, move the secondary up or down the tube as required. tighten the secondary adjustment bolts lightly to hold it and then turn it so it is round in the focuser. you should have a round and central secondary wth a white background (using white paper).

4) tighten the secondary adjusters (three of them) but not overly so and do it sequentialy a little at a time to ensure they are even

5) using the cheshire, centre the circle on the primary (it is reflected in the secondary) to the fuzzy cross hairs in the cheshire - the adjustment here is with the same three secondary adjusters. you may need to loosen two slightly to get the other to move. when central tighten them a little sequentially until 'slightly tight'. ensure the donut is still central.

6) using the three primary adusters put the black dot inside the donut.

7) you are done

you'll notice no mirror clips are referred to as 1) you may not have them and 2) points 1)-5) ensure the mirrors are where they should be.

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