ASTRO: Open Star Cluster M-35

Made from fifteen 1-minute exposures with a Canon Rebel DSLR thru a Brandon
80mm refractor. This is about half of the frame, reduced to about 50% of
original size. The small fuzzy patch is open cluster NGC 2158. It was too
cold to bother with 'darks', but I did do flats and bias frames this time.

For more info on M-35 see: http://www.kopernik.org/images/archive/m35.htm

George N

George Normandin wrote:
Made from fifteen 1-minute exposures with a Canon Rebel DSLR thru a Brandon
80mm refractor. This is about half of the frame, reduced to about 50% of
original size. The small fuzzy patch is open cluster NGC 2158. It was too
cold to bother with 'darks', but I did do flats and bias frames this time.

For more info on M-35 see: http://www.kopernik.org/images/archive/m35.htm

George N

That one sure don't fit my system. NGC 2158 does however.

I think your color blindness is showing. Green-blue stars? Maybe they
are turning that color from the cold.

Snowing here yesterday and today. Supposed to again tomorrow. Spring?
What's that? Snowmobilers were roaring across the lake today.

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".

Nice image, George. The tracking was superb! But unfortunately Brandon seems
to have severe coma.
Best regards,
Gordan

"George Normandin" wrote in message
...
Made from fifteen 1-minute exposures with a Canon Rebel DSLR thru a
Brandon 80mm refractor. This is about half of the frame, reduced to about
50% of original size. The small fuzzy patch is open cluster NGC 2158. It
was too cold to bother with 'darks', but I did do flats and bias frames
this time.

For more info on M-35 see: http://www.kopernik.org/images/archive/m35.htm

George N

"Gordan" wrote

...
Nice image, George. The tracking was superb! But unfortunately Brandon
seems to have severe coma.
Best regards,
Gordan


Gordan,

The "issue" with that old scope (with a Roland Christen triplet) is the
very short focal length. After much discussion with the "refractor experts"
the conclusion is that what the scope has is field curvature, not coma.
There are field flattener lenses, but alas, I have been unable to find one
for a 1.25-inch focuser. This scope was offered (in the mid 1980's) with
both sizes. This scope was also a "free-bee" from the owner of VERNONscope.
More recently Don Yeier tried to find a 2-inch focuser for it in his "junk
pile" of old scope parts, but he had none. The scope came with a 'Barlow
lens' that was designed to screw into the front of the diagonal to correct
this problem, but it adds focal length and, as typical of Brandon, it has a
non-standard Questar thread, so it is un-useable otherwise. Bottom line: I
guess I have to live with elongated stars in the corners and the scope's
real use is as the "finder" for the RC20. We have another one of these
Brandon 80mm's that will go on our Astro-Physics APO when we get the rings
to attach it.

George N

"Rick Johnson" wrote
.....
I think your color blindness is showing. Green-blue stars? Maybe they
are turning that color from the cold.
...........

Rick,

I don't know how to color balance an un-modified Canon DSLR. In fact it
might not be possible. It has almost no red sensitivity thanks to the filter
designed to cut the IR that would be out of focus with a normal camera lens.
The best I can do is to have the software balance the background to an
equal-level 'black'. Because of the way one-shot color works the green
channel is always much brighter than the others (two green pixels for each
red and blue pixel). I personally never make an astro image "look" like what
I think it should. It comes from all of those physics and chem labs at RPI -
"Thou shalt not modify data"!

George N

Now I see. But in the center of the filed Brandon seems to give really sharp
image. I'm sorry that you can't find field flattener that you need. Maybe
you could profit more with this Brandon if you use an imager with smaller
sensor size and smaller pixel size (I saw some imagers with 3,3 micron pixel
size sensors). Then you could make a better use the Brandon's central part
of the field which is optically very good.
Greetings,
Gordan
"George Normandin" wrote in message
...

"Gordan" wrote

...
Nice image, George. The tracking was superb! But unfortunately Brandon
seems to have severe coma.
Best regards,
Gordan


Gordan,

The "issue" with that old scope (with a Roland Christen triplet) is the
very short focal length. After much discussion with the "refractor
experts" the conclusion is that what the scope has is field curvature, not
coma. There are field flattener lenses, but alas, I have been unable to
find one for a 1.25-inch focuser. This scope was offered (in the mid
1980's) with both sizes. This scope was also a "free-bee" from the owner
of VERNONscope. More recently Don Yeier tried to find a 2-inch focuser for
it in his "junk pile" of old scope parts, but he had none. The scope came
with a 'Barlow lens' that was designed to screw into the front of the
diagonal to correct this problem, but it adds focal length and, as typical
of Brandon, it has a non-standard Questar thread, so it is un-useable
otherwise. Bottom line: I guess I have to live with elongated stars in the
corners and the scope's real use is as the "finder" for the RC20. We have
another one of these Brandon 80mm's that will go on our Astro-Physics APO
when we get the rings to attach it.

George N

"Gordan" wrote
....
Now I see. But in the center of the filed Brandon seems to give really
sharp image. I'm sorry that you can't find field flattener that you need.
Maybe you could profit more with this Brandon if you use an imager with
smaller sensor size and smaller pixel size (I saw some imagers with 3,3
micron pixel size sensors). Then you could make a better use the Brandon's
central part of the field which is optically very good.

Gordan,

I think this camera/scope has gone about as far as it ever will. In the
future I plan on trying some other options for wide-field imaging.

George N

Nice image of this "double" cluster.

Stefan

"George Normandin" schrieb im Newsbeitrag
...
Made from fifteen 1-minute exposures with a Canon Rebel DSLR thru a
Brandon 80mm refractor. This is about half of the frame, reduced to about
50% of original size. The small fuzzy patch is open cluster NGC 2158. It
was too cold to bother with 'darks', but I did do flats and bias frames
this time.

For more info on M-35 see: http://www.kopernik.org/images/archive/m35.htm

George N