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09-04-08 I've been at playing
around with astrophotography for about a year and a
half now and decided, a while back that a guide setup is
what I needed to get very long exposures.
Without guiding, I was limited to a maximum of
about 60 second exposures. This was ok, but it took a lot of careful and
tedious processing of the images to bring out the subtle detail
that were hidden in the dark background.
As usual I didn't want to spend a lot of money
on guiding equipment so I perused the web classifieds and swapped e-mail
with members of the various yahoo tech groups (
LXD75 group,
Meade DSI group for example) about what the best choice would
be for a guide scope.
As I found out the Orion 80mm f11 refractor
telescope was a good choice. As luck would have it, I found one on
http://astromart.com
at a good price and bought it. The other thing I wanted was
another DSI-I as a guide camera. I have a Philips SPC900NC web cam that
I used as a guide camera for a while but I had problems with it's
sensitivity, making it difficult to find guide stars in the are
that I was imaging. The other issue was that I was using two
different programs in the process , PHD for guiding and MEADE envisage (
which came with the DSI camera) as the imaging software. Since Envisage
can also guide using Meade cameras I figured that a DSI would allow me
to use envisage exclusively for both functions.
The gods were shining on me, one of the members of the
DSI group read my post and contacted me with the information
that he had a DSI-PRO for sale. What luck! The price was right so
I bought it.
Now I was set. I had everything that I needed to
start guiding and take long exposure pictures. After making an adapter
that allowed me to mount the 80mm on top of my SN8 reflector I was
set. As I quickly found out, autoguiding is an
art in itself. It seems like everything I attempt in this hobby come
with a steep learning curve. However, what makes it all worth
while is the satisfaction when you finally reach the
top and things start working the way you expect.
The first thing I struggled with was aligning the guide
scope with the main scope. The Guide scope sits on three screws in the
mounting ring that you adjust to move the scope
up down left or right. It's not absolutely necessary to have
to two aligned but it helps. The main thing is that you are
able to see a star which to use for guiding once the object
you want to image is framed the way you want. Once that was accomplished came the
next hurdle, actually doing some guiding. I used Envisage to
control the scope for guiding. As I quickly
found out, you still must have a decent polar alignment for things
to start working. So I spent the better part of two hours doing a
drift alignment of the mount ( the
LINKS page for info on polar alignment).
Good balance is also a must. I usually weight the scope a bit heavy
toward the east and North to keep the worm gear loaded on one side. This is the recommended procedure. Click
HERE for info on balancing an equatorial
The next time I went out and tried the guiding again.
During this session I found that I was unable to keep the
scope on target. It would start to drift off and the guider would not
keep up or it would finally yank it back. When
Guiding with envisage you can alter the guiding gain which
changes the aggressiveness of the guide pulse. The program defaults the
gain to 50% (.50) . Not knowing any better I played around with
the gain in that region but nothing that I did seem to help the
problem. Since the target didn't move as much when I turned
the guiding off I decided to try changing the gain to a low
setting. First I tried 30%. Hmm, that seemed a bit better so I
went even lower. I ended up using a guide rate of between 25% and
27%. That seem to have been the answer. Using this setting I'm able to
take exposures for 5 to 8 minutes and probably longer (haven't
tried that yet). If you have a DSI and
want to get some more info on autoguiding with that and Envisage,
Chuck Reese wrote and
excellent
document on how to set up Autostar and Envisage for
autoguiding.
So far so good!! Off to take some pictures
tonight.!!! 11/10/08 Well I thought I had it made using
Envisage to auto guide, alas things didn't work out the way I had
hoped. The guiding started to drift off target. Since auto guiding
was the only way that I was going to be able to
get long exposures, I decided to give PHD a try. PHD is a free
guiding program form
Stark-Labs. After loading the ASCOM 4 and the 4.1.1 driver for the LXD75,
I gave it a shot the next time out. To my delight the program locked
onto the guide star and we were off and running.
The guiding still wasn't 100%, though. The stars in
some of the longer exposures were oblong. After discussing the problem
with one of the guys on the Yahoo groups it was recommended that
I try to get the focal ratio closer between the imaging scope and the
guide scope.
The SN8 I'm using has a f4 ratio and the guide scope
has a f 11 ratio. This makes the guide scope more sensitive to
change and thereby issuing guide commands when the really weren't
needed. Luckily I had an f 0.6 reducer which I was able to
screw onto the nose of the DSI-Pro on the guide scope. This changed the
focal ratio to f6.6. Still a bit long but as it turned out the
guiding improved enormously. That is my
current Guide setup and I'm real happy with it.
06/05/2014 It's a few years later
and I have changed my guiding setup a bit. I'm now using an Orion
50mm mini guide scope and a DSI pro camera guiding with PHD2.
For those that are having problems setting up
PHD here is an excellent adjunct document to the PHD manual
http://www.rosecityastronomers.org/resources/pdf/GuideToGuiding.pdf
. Well written ,easy to understand and fills in the gaps in the original
PHD manual. 07/05/2016
Since I'm now using a TPO10RC scope for imaging I
have found that the arc second difference between the
50mm mini Guider and the main scope is too great ( .5 for the main
and 11 for the mini guider) if gone back to using the ED80 as a guide
scope and put a .67 focal reducer on the main scope. That
combination get's me a bit closer in arc seconds ratio (.82 vs. 3.67 arc
seconds per pix) As mentioned above I use PHD2
as my guide program and found some excellent YouTube Videos on how to
use PHD2 (
https://www.youtube.com/watch?v=PRY2jN3xTBQ ). |
