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collimation ????

beamish

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beamish

beamish

Posted
Posted

okay, collimation scares the living s*** out of me, inspite of reading oodles on the subject.

I feel pretty sure that either my primary is a little off or my secondary is in need of a wee tweak.

I've uploaded a short video onto Youtube here

I would appreciate any thoughts on the subject, cos if I screw up I can't nip down to Nth Wales again !! ( Long story)

Many thanks, Karlo

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Merlin66

Merlin66

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Karlo,

If you look carefully at the "doughnut", you'll see the hole is not central.

If you have a "paint program" like PSP7 etc you can actually use the cursor to measure ( in pixels) the width of the doughnut at 12/3/6/9 o'clock positions to quantify the error.

I'd adjust the primary SLIGHTLY to try and get a more central "hole"

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MidnightSun

MidnightSun

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You are pretty close there. Merlin's idea is as good as any. I have my primary marked in the center and use a laser collimator. Don't let it freak you out, it can always be undone if you go too far one way.

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kniclander

kniclander

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Interesting video Beamish. I note that the out of focus star also shows a couple of small "bites" out of the edge which i think mean that the primary mirror might be clamped too tightly. I make the point for my benefit because that is exactly what I see but I don't know how to adjust the tightness....? Hopefully someone more knowledgeable than me (which doesn't rule out too many people...) will come along and put us right :)

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Merlin66

Merlin66

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Karlo/ Kniclander,

Looking again at the video; the edge distortions I'm sure are due to atmospherics, the main "flat grey" of the extended doughnut shows a good circular outline and is pretty evenly illuminated ( indicating a GOOD smooth, mirror surface)

I'd try a tweek to get the centre "hole" more central (!!??), but you should get good images from this system. Looking good!!

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beamish

beamish

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"Karlo, Cape Newise scopes are well known for their collimation idiosyncrasies. Perhaps they have a user-group? "

Died with the company ! I know that the mirror isn't "pinched" because of how it's fixed- I too am sure it's down to the atmospheric turbulence and more likely the "inner sleeve" of the crayford when the focuser is fully racked in, (can be seen in the mirror),a nearby thin branch !

I will try and tweak the primary to get the centre a little more central

Merlin, I was told when I bought it, that the mirror was better than those available as stnd on the scope (I think 1/8 wave) whereas mine was probably about 1/10 or better, though I don't know how true this is, something to do with it's previous owner (Mr P W) :)

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