I maybe have should have said something
about total setup times because it does not take all night long to do this. I
have completely drift aligned my 900 goto with in 1 hr and 10 minutes of a
complete setup in other words I'm not starting my drift alignment after I my
mount is setup I start the clock when I drop the tailgate of my truck and
begin unloading and assembling my equipment. Another detail I don't wait 15
minutes to detect movement, when you are off at 300x you'll detect movement
easily within a minute of guiding. Mind now that I initially use a polar scope
to align the mount. But the polarscope are not good enough for photography
they are only good enough for getting you into the ballpark so you can get you
drift align going. I will a lot of the time get my drift align going then go
visit my neighbors see what they are doing and then go back and make
adjustments typically two or three adjustments are all that is needed for the
azimuth using the star in the South routine and then I go to the star in the
East and make adjustments to the altitude. A lot of the time if I'm careful
about leveling the pier I don't need to make adjustment to the altitude and
I'm good to go. When I do the go visit the neighbors I'm drift aligned in
about 2 hrs and that is starting from dropping the tailgate of the
truck. As far as a formula is concerned if you going to go to the trouble
of drift alignment you might as well go all the way otherwise if all your
doing is piggy back and as long as you stay with 50mm lens then you are
probably OK once you get to 200mm and longer lenses then you will start
detecting movement. It may not be apparent to eye viewing the negative or
slide put putting it under a magnifier or microscope you will see that
trailing in as little as 15 minutes exposure.
Last I should mention you probably are not going
to get your mount drift align in the kind of times I get mine accomplished.
I'm somewhat practiced at it right now I know the characteristics of my setup
I know that my initial guide star is going to drift down in my guiding
eyepiece and that I'll have to made adjustment accordingly furthermore I also
know that I might have to make adjustments to my altitude and that those
adjustments are going to be minor or none at all. Last even when I'm not doing
photography I'll do a drift alignment just for the practice I even did a drift
alignment during a public star party with my AP 10 inch Maksutov and this was
starting with a daytime alignment just using six inch level and the moon and
Jupiter!
Clear Skies
Dwight L Bogan
In a message dated 11/25/2003 7:46:21 PM US Mountain Standard Time,
serge.theberge@wti.on.ca writes:
Hi Dwight,
Thanks for the reference to Scot Tuckers web
site and for qualifying the
extent to which you drift align your
mount.
I noticed that Scot Tuckers cites 5 minutes with no drift as
being good
enough, while you use 10-15 minutes @ 300X with no
drift. I suspect that
depending on what kind of photo exposure and
magnification you use, that 5
minutes is sometimes "good enough" and some
other (much more infrequent)
times 15 minutes might not be "good
enough". This is why I am looking for
some kind of formula or rule
of thumb that would define maximum polar
alignment error tolerance vs.
exposure time, magnification, etc.
Serge Theberge
Toronto
Centre
RASC