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Old 16-11-2012, 06:04 AM
Jbunky86 (Jason)
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8" F4 newt and QHY10 help please

Hi everyone
I have a new gso F4 8" cf newt and qhy10 osc. Using a mppc spaced at 56mm which seems to give me the least coma. I'm still getting slight vignetting at the corners and I suspect my ccd needs to be tilted slightly.

What's the best way to figure out tilting? Is it a matter of taking flat frames and adjusting the collar? A sort of trail and error procedure?

Lastly would moving the mirror rearwards reduce vignetting? Or would that not make a difference because the focuser would have to move inwards the same amount to reach focus?

Any help would be great

Thanks jas
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Old 16-11-2012, 10:08 PM
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Shiraz (Ray)
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No response from a QHY10 owner, so will jump in with suggestions.

for the best possible results at f4, you have to get the image plane tilt right to within about 40 microns. In average seeing, you can probably get by with somewhat worse than this - but it still needs to be adjusted in very small steps.

I found with my QHY8 (which does not have the adjusting collar - I had to shim it) that measuring the distance from the front surface of camera to the 4 corners of the chip surface was the most reliable approach (used a vernier caliper). I guess you could try the same with the QHY10 and very carefully adjust the collar until the distances from the front surface of the collar to the chip corners are the same.

also make sure that your focuser is not sagging when you add the camera. I had to get a Moonlite to fix this with my f4.

provided vignetting is not excessive, get rid of it with flats.

My f4 with MPCC gives slightly odd star shapes in parts of the FofV regardless of how well it is adjusted - StarTools has a couple of effective algorithms for tidying them up.

regards ray
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Old 17-11-2012, 05:23 PM
Jbunky86 (Jason)
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Thanks mate I will give it a go

Cheers Jason
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