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Old 15-06-2009, 07:01 PM
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JD2439975 (Justin)
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Mirror clips showing?

Gidday all,

I got my EQ6 back last week and was having a bit of a play...
Attached is a shot of Antares, 5x10sec, ISO 800, unguided.
Collimation was off a tad and my first attempt at drift aligning was a bit shoddy to say the least but that's not what concerns me.

You'll notice in the stars halo, 3 dark spikes spaced 120 deg apart, the only thing I can think of is the mirror retainer clips showing.

When I collimated I had to move the secondary mirror up the tube about 5mm to get the laser beam centered on the mirror( collimator to secondary beam).

Also I had to cut 25mm off the base of the tube to achieve focus in the 40D...making the primary about 20mm closer to the secondary than it was in the default setup.

If anything this should be removing any mirror fringe effects by my reckoning(not always right).

Any ideas how to get rid of this effect guys?

Thanks,
Justin.
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Old 17-06-2009, 02:04 PM
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bmitchell82 (Brendan)
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Interesting, i cant give you an exact reply to that because i have the SW 10" which has 8 primary mirror clips. in anycase it shouldn't be affecting the middle of the mirror. its almost as if you have diffraction spikes coming though. very odd.

Other things with your collmination you shouldn't have to move the primary up the tube to get your secondary centered. also is your laser collminated.???

Collminate so that your focal point is just where the camera can reach it so its not hanging out on a limb so to speak!
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Old 17-06-2009, 02:48 PM
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JD2439975 (Justin)
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Thanks for the reply Brendan,

Yep checked the collimation of the laser, all OK.
The primary was only moved up to achieve focus on the camera, as it is I have about 5mm of inward travel left when focus is achieved.

Looking by eye down the focuser the reflection of the mirror clips are near the outer edge of the secondary and centred as you see in most "how to collimate" tutorials.

I can't say I've noticed this effect in other peoples images, it is a little wierd.

JD
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Old 17-06-2009, 04:42 PM
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bmitchell82 (Brendan)
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Ive never seen it either. Are you using the MPCC with the 40d?
I don't worry about the mirror clips when i collminate all i do is use my laser collminator i made to get the angle of the secondary right. eg laser spot pointing to the middle of the primary, and then use the cheshire to get the rotation of the secondary right and the collmination of the secondary to the primary correct.

Apart from that im not sure whats causing your 3 difractions. when you look visually do you see them then? on a bright star i can see the diffraction spikes clearly. have a look at that and see if you still have them then, if so then its something to do with your telescope setup. ide offer to help but i no longer live in good old darwin towne! and i don't know of many people up there, but i know for a fact that there is a small astro community up there. see if you can hook into them?.
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Old 17-06-2009, 05:05 PM
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JD2439975 (Justin)
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Not using the MPCC, it's in the post to me as we speak (been a long wait for it).

Next time I'm visual I'll take a closer look to see if it's there, might try photographing through a barlow as well, see if that makes any difference.
More experimenting needed I think (when I get the replacement Synscan controller back from Andrews, I am having failure problems with this mount).

Interesting you went from Darwin to Perth, I did it the other way around.

Thanks Brendan,
JD
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Old 17-06-2009, 10:45 PM
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AstroJunk (Jonathan)
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Bright stars show up all sorts of interesting effects. Have a look at this image of Sirius A and B I took a couple of years back - the intresting diffraction effect you can see on the horizontal plane is caused by the focusser tube on my newt. It wasn't even in the light path of the mirror!
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Old 18-06-2009, 03:00 AM
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JD2439975 (Justin)
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Thought I'd check some stars from the digital sky survey in worldwidetelescope.
In this screen capture thier setup makes Mirzam look like an unfinished Deathstar.

A bit like a scopes fingerprint.
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