ASTRO: A2065

Scraping the hard drive clean...A weak effort taken last year in May. 3 ten
minute shots were all I did. Guide stars are few and far between in this
area. Also a 2000mm f.l. 14" SCT (f/5.5) is not enough f.l. to resolve this
cluster well enough. We might be putting a .7 reducer in to get a little
more f.l. That would also match better with the ST9 pixcels. Hey
Rick...what can you do with this cluster.

Joe

J McBride wrote:

Scraping the hard drive clean...A weak effort taken last year in May. 3 ten
minute shots were all I did. Guide stars are few and far between in this
area. Also a 2000mm f.l. 14" SCT (f/5.5) is not enough f.l. to resolve this
cluster well enough. We might be putting a .7 reducer in to get a little
more f.l. That would also match better with the ST9 pixcels. Hey
Rick...what can you do with this cluster.

Joe


My standard 2x2 binning would give about twice the image scale you have
in this shot. Looks like this is one to wait for that one or two nights
a year with seeing I can use 1x1 binning on but of course it would be
out of season that night.

What happens when you take out the reducer? Is the field too curved?
That would make the C14 ST-9 almost identical to my set up, just a
smaller field of view. Think the ST-9 has 20 micron pixels while mine
has 18 when binned 2x2. You run f/11 while I run f/10 which just about
compensates for my smaller pixels. The difference would be immaterial,
only about 1% by my quick estimate. Considering scope focal length and
reducer powers are only approximate call it identical. You would need 4
times the exposure, still the ST-9 is a bit more sensitive than the
STL-11000 so wouldn't need quite as much as I would.

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
...


J McBride wrote:

Scraping the hard drive clean...A weak effort taken last year in May. 3
ten
minute shots were all I did. Guide stars are few and far between in this
area. Also a 2000mm f.l. 14" SCT (f/5.5) is not enough f.l. to resolve
this
cluster well enough. We might be putting a .7 reducer in to get a little
more f.l. That would also match better with the ST9 pixcels. Hey
Rick...what can you do with this cluster.

Joe


My standard 2x2 binning would give about twice the image scale you have in
this shot. Looks like this is one to wait for that one or two nights a
year with seeing I can use 1x1 binning on but of course it would be out of
season that night.

What happens when you take out the reducer? Is the field too curved?


Rick (and others)

the reducer actually reduces the radius of the focal surface which means it
makes the image surface more strongly curved

removing the focal reducer will therefore tend to make the focal surface
flatter.

Here's one source for further reading on the topic:
-Rutten and Van Venrooij "Telescope Optics: a Comprehensive Manual for
Amateur Astronomers" pp 158-159


That would make the C14 ST-9 almost identical to my set up, just a smaller
field of view. Think the ST-9 has 20 micron pixels while mine has 18 when
binned 2x2. You run f/11 while I run f/10 which just about compensates
for my smaller pixels. The difference would be immaterial, only about 1%
by my quick estimate. Considering scope focal length and reducer powers
are only approximate call it identical. You would need 4 times the
exposure, still the ST-9 is a bit more sensitive than the STL-11000 so
wouldn't need quite as much as I would.


I used the C14 I had with a Tektronix TK1024 sensor in my old FLI Dream
Machine: when I put it on the beam spliter and the camera angle adjuster, my
focal ratio wound up as f/12.46 (4430mm) due to the very long image train.

Using the 24x24 micron pixels of the TK1024 (1.12 arc-sec/pixel) I got nice
results in my typical 3 -4 arc-sec seeing. When the seeing improved into the
twos it was hard to take advantage of it.

The TK1024 is pretty sensitive and the big pixels used on the C14 were a lot
of fun because things were pretty darn fast.

The only thing I found was that the C14 needs some help in guiding due to
mirror shift considerations. somehow you need to guide through the scope:
either self guided or beam splitter or pickoff mirror; something to avoid
the separate guidescope that is so problematic due to differential mirror
movement relative to the guider.



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".

Richard Crisp wrote:


removing the focal reducer will therefore tend to make the focal surface
flatter.

Here's one source for further reading on the topic:
-Rutten and Van Venrooij "Telescope Optics: a Comprehensive Manual for
Amateur Astronomers" pp 158-159

Interesting, I was under the impression they corrected for the curved
field besides reducing the focal length. Wonder why they don't?
Obviously I'm no optician!


Using the 24x24 micron pixels of the TK1024 (1.12 arc-sec/pixel) I got nice
results in my typical 3 -4 arc-sec seeing. When the seeing improved into the
twos it was hard to take advantage of it.


That's why I went with a large CCD but relative small pixels and binning
rather than the reducer method. That way I could just change the
binning. No need to mess with the scope set-up, I have severe arthritis
so doing so is a real pain! I just change the binning when seeing
permits like it did the other night for 2805 and friends. I only did a
quick and dirty process hoping seeing would be good again last night but
the front got here faster than expected so guess it is back to doing a
better job on it as I doubt I'll see that seeing for months to come.


Rick

"Rick Johnson" wrote in message
news


Richard Crisp wrote:


removing the focal reducer will therefore tend to make the focal surface
flatter.

Here's one source for further reading on the topic:
-Rutten and Van Venrooij "Telescope Optics: a Comprehensive Manual for
Amateur Astronomers" pp 158-159

Interesting, I was under the impression they corrected for the curved
field besides reducing the focal length. Wonder why they don't? Obviously
I'm no optician!


Well they may. I was speaking only to focal reducers, not to combo units. If
that's what you were speaking to, then we need to clarify we were talking
about different things.




Using the 24x24 micron pixels of the TK1024 (1.12 arc-sec/pixel) I got
nice results in my typical 3 -4 arc-sec seeing. When the seeing improved
into the twos it was hard to take advantage of it.


That's why I went with a large CCD but relative small pixels and binning
rather than the reducer method. That way I could just change the binning.
No need to mess with the scope set-up, I have severe arthritis so doing so
is a real pain! I just change the binning when seeing permits like it did
the other night for 2805 and friends. I only did a quick and dirty
process hoping seeing would be good again last night but the front got
here faster than expected so guess it is back to doing a better job on it
as I doubt I'll see that seeing for months to come.


Rick

The telescope and equip. belongs to my astronomy club. It is kinda set up
for everyone to use...even though I am the only one who really uses it on a
regular basis. It was decided that f/5.5 would frame most of the deep sky
objects that might make pretty pics and still let those who want to serch
for asteroids or SN be able to do that. I am trying to get the .7 reducer
put in so that the images are not so close to getting under sampled...faint
stars are almost 4 pixcels. Thats a little close. But club politics and
all, plus downed equipment has left me scouring the harddrive for older
images.

BTW the C14 is mounted on the Paramount 2000 and is housed in a dome. We
have problems with the mount and dome software getting along plus a few
wrong buttons pushed along the way. The flawless part is the Optec imaging
system from the TCF down to the IFW and focal reducer. If it were mine I'd
shoot @ f/11 and use a ST2K or the ST11000 like what you have. Its hard to
have a turn key system when everybody turns the key differently.

Joe






"Rick Johnson" wrote in message
...


J McBride wrote:

Scraping the hard drive clean...A weak effort taken last year in May. 3
ten
minute shots were all I did. Guide stars are few and far between in
this
area. Also a 2000mm f.l. 14" SCT (f/5.5) is not enough f.l. to resolve
this
cluster well enough. We might be putting a .7 reducer in to get a
little
more f.l. That would also match better with the ST9 pixcels. Hey
Rick...what can you do with this cluster.

Joe


My standard 2x2 binning would give about twice the image scale you have
in this shot. Looks like this is one to wait for that one or two nights
a year with seeing I can use 1x1 binning on but of course it would be
out of season that night.

What happens when you take out the reducer? Is the field too curved?
That would make the C14 ST-9 almost identical to my set up, just a
smaller field of view. Think the ST-9 has 20 micron pixels while mine
has 18 when binned 2x2. You run f/11 while I run f/10 which just about
compensates for my smaller pixels. The difference would be immaterial,
only about 1% by my quick estimate. Considering scope focal length and
reducer powers are only approximate call it identical. You would need 4
times the exposure, still the ST-9 is a bit more sensitive than the
STL-11000 so wouldn't need quite as much as I would.

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 picture Joe, this is really a crowded place.

Stefan

"J McBride" schrieb im Newsbeitrag
...
The telescope and equip. belongs to my astronomy club. It is kinda set up
for everyone to use...even though I am the only one who really uses it on
a
regular basis. It was decided that f/5.5 would frame most of the deep sky
objects that might make pretty pics and still let those who want to serch
for asteroids or SN be able to do that. I am trying to get the .7
reducer
put in so that the images are not so close to getting under
sampled...faint
stars are almost 4 pixcels. Thats a little close. But club politics and
all, plus downed equipment has left me scouring the harddrive for older
images.

BTW the C14 is mounted on the Paramount 2000 and is housed in a dome. We
have problems with the mount and dome software getting along plus a few
wrong buttons pushed along the way. The flawless part is the Optec
imaging
system from the TCF down to the IFW and focal reducer. If it were mine
I'd
shoot @ f/11 and use a ST2K or the ST11000 like what you have. Its hard
to
have a turn key system when everybody turns the key differently.

Joe






"Rick Johnson" wrote in message
...


J McBride wrote:

Scraping the hard drive clean...A weak effort taken last year in May.
3
ten
minute shots were all I did. Guide stars are few and far between in
this
area. Also a 2000mm f.l. 14" SCT (f/5.5) is not enough f.l. to resolve
this
cluster well enough. We might be putting a .7 reducer in to get a
little
more f.l. That would also match better with the ST9 pixcels. Hey
Rick...what can you do with this cluster.

Joe


My standard 2x2 binning would give about twice the image scale you have
in this shot. Looks like this is one to wait for that one or two nights
a year with seeing I can use 1x1 binning on but of course it would be
out of season that night.

What happens when you take out the reducer? Is the field too curved?
That would make the C14 ST-9 almost identical to my set up, just a
smaller field of view. Think the ST-9 has 20 micron pixels while mine
has 18 when binned 2x2. You run f/11 while I run f/10 which just about
compensates for my smaller pixels. The difference would be immaterial,
only about 1% by my quick estimate. Considering scope focal length and
reducer powers are only approximate call it identical. You would need 4
times the exposure, still the ST-9 is a bit more sensitive than the
STL-11000 so wouldn't need quite as much as I would.

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".