RE: Survey Strategy

[Tom Droege <tdroege2@earthlink.net>]

Rob and all,

The next version of the declination drive will be faster.  The current 
version is so slow to get the gear ratio high enough that the carriage does 
not move with the motor off.  I will just leave the motor on all the time 
with the new version and will be able to use a lower gear ratio 
motor.  Also I will do away with the declination clamp motor.  No clamp.

Note that unless you go off and think for hundreds of seconds, one never 
needs to take a clearing scan after the first one with the present MPP 
clocking.  The dark current variations are very small compared to the sky 
noise.  So one just can't see any error due to variations between images 
unless there is a very large difference in spacing between images.  So plan 
never to do a clearing scan after the first.  Just looked it up.  We expect 
about 1 adu per second of dark current at -15 C.  I get 30 to 60 adu per 
second of sky brightness.  I doubt that the dark current will ever be of 
much concern.

Tom

At 01:45 PM 10/4/02 -0600, you wrote:

>Yup.  This is exactly what I'm doing.  I'm also keeping track of the last
>time a picture was taken so I can move during the DARK exposure
>(transitioning from object to dark) without executing a clearing scan.
>
>I may work on moving RA and DEC at the same time to increase the possible
>distances traversed during the transfer.  Otherwise, moving DEC on ROB takes
>most of the available time (45.5 (steps/second) / 120 (steps/degree) * (45s
>- 20s clamp open/close) = 5.7 degrees).  I need to open the DEC clamp on ROB
>400 steps to not bind with the brake, providing a much smoother DEC
>movement.
>Moving both mechs at the same time will just entail breaking down the DEC
>move into multiple moves which coincide with the desired RA move timing.
>Easy ;-)
>
>Unless I am mistaken though (in reference to Arne's tech note), the minimum
>exposure is around 20-30 seconds, the time it takes to download the data
>from the memory card.
>
> > -----Original Message-----
> > From: Tom Droege [mailto:tdroege2@earthlink.net]
> > Sent: October 04, 2002 1:18 PM
> > To: Creager, Robert S; tass@listserv.wwa.com
> > Subject: RE: Survey Strategy
> >
> > 1) close the shutter
> > 2) start the scan
> > 3) look to see what you want to do next
> > 4) move the telescope to the new position
> > 5) start the RA drive going to get rid of backlash
> > 6) test for the block done
> > 7) note the time and open the shutter to start taking the next image
> > 8) go to 1)
> >
> > Note that with this sequence, or something like it, one is dead for
> > exactly
> > 46 seconds between frames.  You should always be able to get ready for the
> > next frame in this time.  I do not think that you will be able to see any
> > effects from moving motors, etc., in the data, but one should check.