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Astimatism in LX5


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#1 smith99

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Posted 07 August 2008 - 04:42 PM

Is there any way to correct the astigmatism in the optics of my LX5? I tried a mask and can get good star images thru a 3" circular diameter opening but not with the whole aperture.

#2 Mark Sibole

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Posted 08 August 2008 - 09:39 PM

Have you tried to columinate the scope?
There may be a mis alignment between the primary and secondary mirror.
I know the LX5 is an old scope and I do not know what kind of optics were used way back then but it may simply be out of adjustment.

Regards

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#3 smith99

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Posted 10 August 2008 - 04:17 AM

Thanks for the reply!  Yes, I have collimated the scope by centering the image of the secondary against the image of the mirror on a de-focused star. Although that is important, I still get a poor star image upon focusing again. A slightly defocused star image is football shaped and on the other side of focus, it is again football shaped, oriented 180 deg from the previous image. I was wondering if the Televue eyesight astigmatism corrector might help or perhaps a coma corrector.

#4 Mark Sibole

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Posted 10 August 2008 - 07:39 PM

Im not sure if that will help.
The coatings could finally be breaking down.
Like I stated im nor real familiar with the LX5 so I dont know what direction to go.
Sorry I couldnt be more help.

Regards

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#5 smith99

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Posted 20 August 2008 - 06:26 PM

After experimenting on this for a while, I've found that I can effect the image by loosening the retaining ring and rotating the corrector plate with respect to the optical tube. I also found that the secondary has a little lateral play on the corrector plate as well. I haven't totally fixed the "astigmatism", if that's what it really is, but I can effect the image and make some modest improvements. I also tried backing out the collimation screws on the secondary almost all the way and then recentering the image of the secondary, but that didn't really effect anything.

#6 avenosod

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Posted 29 August 2011 - 08:57 AM

Try it again by using ONLY an eyepiece, no diagonal. Rotate eyepiece to see if oval ratates with it. If yes, bad eyepiece. Only make adjustments to corrector plate and/or secondary witout diagonal. Did you return corrector to original position. It came factory set so this is important. Secondary can come loose and move or rotate. I would try rotating and re-centering secondary only to get round out-of-focus image. Then collimate in the time tested manner.

Dennis




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