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Old June 22nd 09, 04:55 AM posted to alt.binaries.pictures.astro
Rick Johnson[_2_]
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Default ASTRO: First light, AP155EDF f/7 and PL39000C, target M8/M20

Richard Crisp wrote:
I have been attempting to use the '155 f/7 with the PL39K for three weeks
now. The faster focal ratio, f/7 versus the f/9 of the '180edt, means nearly
a 2x improvement in light gathering rate with a modest increase in image
scale: 1.15 versus 0.87 "/pixel. Finally the weather cooperated on Saturday
night.

I took 4.75 hours of exposure on Sat night using 15 minute subexposures.

the full 39 megapixel resolution on the linked page below is interesting:
there are a lot of stars in there!

http://www.narrowbandimaging.com/m8_...pl39K_page.htm


Nice resolution on the central "star" of M20. Well resolved.

Glad someone sees sky. At least lately the clouds have given up some
rain. Well shy of what's needed but it helps. Still two solid months
of clouds and only 2" of rain is not a good trade.

I'm a bit lost on the image scale. 155mm at f/7 is 1085mm focal length
while f/9 at an aperture of 180mm is 1620 or a 49% increase. Increasing
..87 by 49% gives a 1.3" pixel. Does the flattener make the difference?

Rick

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