Richard Crisp wrote:
"Rick Johnson" wrote in message
ster.com...
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?


You are right about image scale Rick. I went by memory thinking my focal
length was 1215mm. It is 1085 as you said.

the image scale is 1.27"/pixel instead of the 1.15 I stated above.

so moving from the '180 f/9 at 1620 to the '155 f/7 at 1085mm gives me
1.27"/pixel instead of 0.87"/pixel

I did a lot last week: Sunday I flew to Taipei and had a week's worth of biz
meetings, flew home friday evening, drove to the ranch upon landing, set up
the scope and imaged. I got crap for data that night but found the warts and
fixed them for sat night. I guess in the confusion I just did not remember
my focal length correctly.. thanks for double-checking!


here is the view from my hotel room.... that's Taipei 101, the tallest
building in the world (at least today it is).


That's one massive building. The Asians seem to be building "The
Tallest Building" every few years.

I think it is too many years as a CPA but when numbers just don't work
something in my brain goes off. I know its wrong, just not what or by
how much. But I have to figure it out or go nuts thinking about it.

I hate long flights all cramped up. Going east always gives me a three
or four day period I'm worthless for anything. No way I could have even
tried imaging after that return trip. West doesn't seem to bother me.
Lived next to a Pan Am pilot for years when I lived in Lincoln Nebraska.
He flew a round the world route from LA returning to Kennedy about 6
days later. They only set those routes going west. East flights were
only one leg if crossing more than 2 time zones. He had the seniority
that he could and did refuse anything going east. Not bad gig, fly
around the world once every two weeks, work for 6 days and be off for 8.

Rick

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