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Old 04-04-2012, 07:06 PM
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sopticals (Stephen)
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sopticals is offline
Join Date: Jun 2010
Location: Oamaru, New Zealand.
Posts: 206
Smile Uncoated 22" mirror first light.

Hi interested glass pushers,

Just come inside from first light experience of my recently finished 22" f5.36 (fl 3000mm), mirror, (as yet uncoated). Unfortunatly my sky was 90% plus cloud covered and my dob structure has yet to birth a finder scope, so views were confined to the moon (when I eventually located it) as it briefly appeared for a minute or so from time to time.

Using a GSO 30mm 2" Superview (67deg FOV), the magnification 100x. The 91% Gibbous moon took most of the field of view. Focus came up nice and sharp, with small craters and surface wrinkles standing out with good contrast. At the boundary where the moons bright limb meets with the dark background of deep space, I was pleased with the sharpness of the boundary going from the brightness of the lunar fully lit surface to the sudden blackness of empty space.

Even though an uncoated mirror reflects around 5% of the light falling on it, a mirror of 22" (uncoated) still captures the light of a 5" coated mirror, so not going to be great on DSOs. So next step is to put on a coat of silver, and it should be ready to go.

PS. Would have liked to try more magnification, but with the limiting viewing, and difficulty in locating a target object without a finder decided to call it a night. My finder is going to be a Skywatcher 4.5" f4.44 newt.

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