ASTRO: First light, AP155EDF f/7 and PL39000C, target M8/M20

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

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

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

"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).

Mighty image Richard.
The faster setting suits the camera well obviously. 0.87"/pixel were
probably a bit of an "overkill" for those large nebulae, so you probably
didn't lose anything by going for the shorter focal length.

Stefan

"Richard Crisp" schrieb im Newsbeitrag
m...
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

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

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

"Stefan Lilge" wrote in message
...
Mighty image Richard.
The faster setting suits the camera well obviously. 0.87"/pixel were
probably a bit of an "overkill" for those large nebulae, so you probably
didn't lose anything by going for the shorter focal length.

Stefan

Thanks Stefan

the only reason it was first used on the '180 was because it was set up
already for the PL9000 and robofocus.

My key obstacle to deploying it on the '155 was coming up with a way to
connect my robofocus to it. That wasn't very hard: it was harder waiting
three weeks for the skies to clear.....

"Rick Johnson" wrote in message
ster.com...

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.


I finally managed to sleep on the return trip. Slept most of the way. Biz
class seats make a huge difference!

usually going East is the killer for me. This time it was heading west: the
departure from SFO is 1:40AM so it has already been a long day. Then the
flight is 14 hours and when yuo land it is 6am.... the beginning of yet
another long day. Only way to make this work is to find a way to sleep on
the way over....

But I was whacked all week over there.... I do this every month now :-(