SOME NOTES ON CHAINED GUIDING - By Chris Schur

     After about a year or two of playing around with the high speed superfilms,
and getting fast but very grainy results, many astrophotographers decide to
try their hand at the slower and finer grained emulsions.  But to their 
dismay, even the hypered 400 speed films require an hour exposure at f/5 to
get anything decent, or at best, with an f/2.8 telephoto a good 15 minutes
is needed.  For most, 15 minutes is a long time to be at the guide scope,
let alone an hour or more!  Now I'm going to let you in on a secret.  There
is a way to guide for as long as you have to get those killer shots, yet
still maintain your sanity.  It's called "Chained Guiding", and for myself
anyway, has allowed me to go over an hour exposure on slow ultra fine
grained films with my f/5 newtonian and not get the least bit tired or 
saddle sore in the act.  

     The principle is simple:  Break up the long exposure into smaller 
chunks, say four 15 minute exposures to achieve an hour long one.  To 
do this in a newtonian, a shutter was installed in the main focuser so 
that the off axis guider could still see the star when the light
to the film was shut off.  Once set up on my subject, and I'm ready to 
begin shooting, I start the timer, and begin.  15 minutes later, and 
before I get fatigued, the shutter is closed down and a five minute coffee 
break begins!  After I've stretched a bit, the exposure is resumed for 
another 15 minutes.  This process is repeated until I have accumulated 
about an hours worth of exposure, which takes about an hour and a half.  
But its easy to do!  I guide my best in 15 minute or less exposures, yet
here is an hour exposure with my best guiding and I'm not the least bit 
exhausted.  One can do this trick all night long, and get those top rate 
photos with a minimum of effort.  

     The same method can be used of course for piggyback shots.  Lets say 
you haven't done much astrophotography before, and want to turn out a 
decently guided 15 minute exposure.  By chaining three five minute shots 
together by covering the lens during your coffee (or tea) breaks and 
resuming you can do it.  This method allows individuals that have never 
in the past been able to go over  five minutes or so to do those longer 
exposures, and perhaps for the first  time, use the slower higher 
resolution films.