ASTRO: M27

Hello,

I don't post very often here but I need some feedback for my 8" LX200gps. I
use a DSIC2 for imaging and a DSIC for guiding. I can't seem to get the
scope to track well for more than 30 sec. at a time without getting star
trails. I tried PEC training, maybe need to work on that more, but have
gotten whipped into submission that I can't get byond 30 sec subs. If there
is some info out there on the net, like PEC for Dummies, to get me pointed
in the right direction, I would appreciate it. :-) This pic is from last
night. 21 sec exposure, 40 images stacked by envisage. Thanks a bunch guys!

Barry Clay

Hi Barry, Try manually guiding you shots at first to see what your drive is
doing during the exposures. You might have other problems going on. PEC
should not be an issue for 30 sec shots. I've seen people take 2 min shots
with LX200's with the PEC off.

Joe


"BClay" wrote in message
news
Hello,

I don't post very often here but I need some feedback for my 8" LX200gps.
I
use a DSIC2 for imaging and a DSIC for guiding. I can't seem to get the
scope to track well for more than 30 sec. at a time without getting star
trails. I tried PEC training, maybe need to work on that more, but have
gotten whipped into submission that I can't get byond 30 sec subs. If
there
is some info out there on the net, like PEC for Dummies, to get me
pointed
in the right direction, I would appreciate it. :-) This pic is from last
night. 21 sec exposure, 40 images stacked by envisage. Thanks a bunch
guys!

Barry Clay

you didn't say anything about your polar alignment method

if you aren't using drift alignment you should

that's really the only way to be assured you are properly aligned

if you aren't properly aligned there will be a bias that causes the guiding
to always be in error in the same direction

normal guiding problems are more random. polar alignment problems result in
the guiding always being off in the same direction


"BClay" wrote in message
news
Hello,

I don't post very often here but I need some feedback for my 8" LX200gps.
I use a DSIC2 for imaging and a DSIC for guiding. I can't seem to get the
scope to track well for more than 30 sec. at a time without getting star
trails. I tried PEC training, maybe need to work on that more, but have
gotten whipped into submission that I can't get byond 30 sec subs. If
there is some info out there on the net, like PEC for Dummies, to get me
pointed in the right direction, I would appreciate it. :-) This pic is
from last night. 21 sec exposure, 40 images stacked by envisage. Thanks a
bunch guys!

Barry Clay

BClay wrote:
Hello,

I don't post very often here but I need some feedback for my 8" LX200gps. I
use a DSIC2 for imaging and a DSIC for guiding. I can't seem to get the
scope to track well for more than 30 sec. at a time without getting star
trails. I tried PEC training, maybe need to work on that more, but have
gotten whipped into submission that I can't get byond 30 sec subs. If there
is some info out there on the net, like PEC for Dummies, to get me pointed
in the right direction, I would appreciate it. :-) This pic is from last
night. 21 sec exposure, 40 images stacked by envisage. Thanks a bunch guys!

Barry Clay

Good tracking starts with highly accurate polar alignment. Even a
guider can't compensate for much error here as that will just hold the
guide star still while the entire field of view rotates around it. Rate
of rotation is proportional to the amount of polar alignment error and
how far the guide star is from the field of view being photographed.

What tracking error do you see over 16 minutes (two turns of the worm)?
If there is a drop or rise in declination then it is not well polar
aligned. PEC can't compensate for polar alignment error though I believe
the GPS system can program in a constant error for DEC. That's rather
useless as DEC error is due to rotation around a misaligned pole so will
vary with time and position. I doubt it takes that into account. If the
error just causes stars to retrace back and forth along an east-west
line then PEC should eliminate a lot of that type of error.

Then there are the really dumb errors that can nail you. I spent half a
night pulling my hair out because somehow I had managed to set the drive
to solar rather than sidereal rate! Club member won't let me forget
that one. If the scope is out of balance it won't track well. I think
with the GPS solar rate is at about 60.1 HZ. Check the manual. It
should be the default setting I would think. I somehow change the
default on an older one to solar.

Tracking down the problem requires first knowing exactly what the error
looks like and going from there. Something like dirt in the gear train
can cause random errors as the dirt is moved along the worm or drive
gear. I change the grease once a year to start clean. I just did that
during my current cloud season.

On training PEC pick a night of very good seeing or you will be
programming in lousy seeing! If you use a guider camera then don't
bother with PEC the guider will handle it. PEC is no more accurate than
the programming. I use the CCD to do the programming. I don't think
your software allows that so you'll need a good high power cross hair
eyepiece for the job. Align the cross hairs so one is exactly parallel
to the declination axis. For now ignore errors up and down the axis.
You will only play with the east west buttons to hold the star somewhere
on the north south line. With it in learn mode do so for one full
rotation of the worm. (8 minutes I think for your scope). Then save
the info. If you want to try declination compensation do the same
holding it to the RA axis but do so for longer than your exposure time.
If you find the star going first north then south of the RA cross hair
then seeing is too lousy to try programming anything. Any declination
drift will be only in one direction. Be sure you are training the right
axis! For now I'd forget dec errors. Correct them with better polar
alignment.

I've not looked at a GPS manual for some time so things may have changed!

Rigidity is another key to accurate guiding. It's amazing how easily
slop slips into a system. Even slop you can't feel can ruin your shots.
Be sure everything is rock solid.

I don't use PEC here as the Paramount's worm errors are less than my
seeing most nights. Only on nights of really good seeing or if I'm
taking longer than normal exposures do I even guide. About 80 % of the
shots I post were taken unguided with 5 and 10 minute exposures at 140"
focal length. Precise polar alignment does the work for me.

Attached is my shot of M27 from last year. It was taken when I still
had Meade's focuser on the scope. It was too weak to hold the camera at
right angles to the optical axis causing stars to elongate toward the
edge of the field. It has since been replaced with a far superior (and
far more expensive Van Slyke/Robo 3" focuser that doesn't sag or
vignette as the Meade focuser did. I should put it up for sale as I
doubt I'll ever use it. For a small light CCD it would be fine, just
not a big chip or heavy one and mine is both.

The attached photo used 5 5 minute shots for the image and 15 five
minute ones for color data all unguided and without PEC. Nothing
compensates for accurate polar alignment!

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".

Hi Barry,

What image acquisition program are you using? To improve your tracking,
you need to make your exposure time as short as possible to get a star to
show above the background noise. Also, your tracking will improve with the
quality of your equatorial alignment. PEC, unless it is very badly off, does
not affect your tracking as much as bad polar alignment.

--
Tandy W. Carter Jr.

http://home.att.net/~tandy.carter/


"BClay" wrote in message
news
Hello,

I use a DSIC2 for imaging and a DSIC for guiding. I can't seem to get the
scope to track well for more than 30 sec.

Nice shot Barry.
I you have bad luck you could simply have a scope that can't go any longer
than 30 seconds at the imaging scale you use. My LX200 can probably go for
60 seconds unguided with a good chance of round stars. 120 seconds would
already be a 50/50 chance.
I think that you would have to guide (manually or with an autoguider) to
have a high success rate at anything over 60 seconds.

Stefan

"BClay" schrieb im Newsbeitrag
news
Hello,

I don't post very often here but I need some feedback for my 8" LX200gps.
I use a DSIC2 for imaging and a DSIC for guiding. I can't seem to get the
scope to track well for more than 30 sec. at a time without getting star
trails. I tried PEC training, maybe need to work on that more, but have
gotten whipped into submission that I can't get byond 30 sec subs. If
there is some info out there on the net, like PEC for Dummies, to get me
pointed in the right direction, I would appreciate it. :-) This pic is
from last night. 21 sec exposure, 40 images stacked by envisage. Thanks a
bunch guys!

Barry Clay