Canon 20D + Timer remote

Hi all,
I am looking for a way to take multiple exposures of several minutes each
of the same object. I want to use the mirror lockup feature to help minimize
vibration. From reading the 20D manual it looks like the first press of the
shutter control causes the mirror to lockup. The second push initiates the
exposure.

I do not have the remote timer yet but my question is this: Using the remote
timer, if I set an interval time of 10 seconds, exposure time of 8 minutes
and exposure count of 10, will I actually get 10 exposures or 5? If the
answer is 5, that would mean that the mirror would lockup for 8 minutes,
then the shutter would open for 8 minutes. Is this correct?

Thanks,
Bill

"Bill Cotten" wrote in message
...
Hi all,
I am looking for a way to take multiple exposures of several minutes each
of the same object. I want to use the mirror lockup feature to help
minimize
vibration. From reading the 20D manual it looks like the first press of
the
shutter control causes the mirror to lockup. The second push initiates the
exposure.

I do not have the remote timer yet but my question is this: Using the
remote
timer, if I set an interval time of 10 seconds, exposure time of 8 minutes
and exposure count of 10, will I actually get 10 exposures or 5? If the
answer is 5, that would mean that the mirror would lockup for 8 minutes,
then the shutter would open for 8 minutes. Is this correct?


With the 10D firmware, mirror lockup is enabled, disabled, and/or given a
timed value to be in effect before the exposure is taken (using the camera
menu system, not the TC). Once enabled, it is only in effect for Bulb mode
(I'm pretty sure).

The TC-80N3 timer/controller has 4 effective settings: Delay start, Interval
between exposures, Exposure time, and Exposure count. All other settings are
made on the camera itself: putting the camera into manual mode, setting it
to Bulb mode, and adjusting the ISO setting are the most significant for
astro, in particular.

When the user initiates the sequence by pressing the start button on the TC,
the first thing that will happen is the user set start delay. This is to
allow the user time to let go of the TC, and let any vibrations caused by
handling to dampen (I set mine to 10 seconds, which is plenty). The second
thing to happen is the camera firmware intiated mirror lockup, using the
time that the user set in the menu, this allows vibrations from the
mechanical action of the mirror flip up to dampen before starting the
exposure (I set mine to 3 seconds). The third thing that happens is the
exposure, for the length of time set by the user using the TC (anyhwere from
30 seconds, to several minutes). The fourth thing to happen, is a decrement
of the exposure count, before starting subsequent exposures.

On subsequent exposures (depending on the exposure count), the start delay
is no longer used, and the Interval timer kicks in, causing the camera to
effectively sleep for the set time. To allow the CMOS sensor to cool and
keep noise to a minimum, it is recommended that this be set to at least 30
seconds (what I use). This feature is intended for use in time lapse
photography, which we don't really care about for most astro-images, but for
the purpose of cooling the camera.

30 second intervals, plus 3 seconds for mirror lockup becomes a significant
chunk of time when you start taking sequences of 30 exposures set to 5
minutes each.

I set up an exposure, calculate the total time, and then go do something
else for a while.

Hope that helps some,
Stephen