that's an eclipse I surely won't get in Italy :-)
vostok, I don't exactly understand what you want to obtain:
1) a video showing the day getting darker and then brighter again
2) a graph of luminositygoing down and up
3) what else???
1) a video showing the day getting darker and then brighter again
I don't kow where you are located, but if you are not near totality (and you don't see a very strong eclipse) this can be VERY difficoult, as other factors will change luminosity more than the eclipse.
I mean, if you have a 30% eclipse starting at 8:00 in the morning and ending at 10:00, you have two main factors changing luminosity:
- the day that progresses, with the sun rising over the horizon
- the eclipse
Which one is stronger??
anyway, if this is what you want to obtain I would do the following:
- before the eclipse starts, shoot a test frame. See what exposition data the camera used (for example, f/4 1/100s)
- put the camera in manual mode, set those values (f/4 1/100s) manually. The camera will now shoot always with those values.
- use the basic intervalometer script, and just tell the camera to shoot one shot every X seconds. The frames will all be exposed identically, and you hopefully should have your result.
The risk is that if for example you start at 8 in the morning, at 10 in the morning everything will be over-exposed.
You could then be more ambitious and do (for example) 5 movies each one with a different exposure.
The idea is to use custom auto-timer mode (a standard feature of your camera, probably) and say to your camera to always take 5 shots. Then, use "bracketing in continuous mode" (a CHDK feature) saying for example to bracket 2 EV.
In this mode, every time you take a shot your camera will take 5 shots with a wide range of exposures: 0, +2EV, -2EV, +4EV, -4EV.
then, follow the steps I said before and you will have a LOT of pictures, that are divided in 5 series with different exposures:
0001 0EV
0002 +2EV
0003 -2EV
0004 +4EV
0005 -4 EV
0006 0EV
0007 +2EV
0008 -2EV
0009 +4EV
00010 -4 EV
0011 0EV
0012 +2EV
....
if you only use the frames 0001, 0006, 0011 etc (only frames ending in 1 or 6) you have the "standard movie"
If that movie is overexposed, you can use frames 0003, 0008, 0013 etc (only frames ending in 3 and 8 ) to get a darker movie (-2EV)
Using frames 0005, 0010, 0015 etc (only frames ending in 5 and 10) to get an even darker movie (-4EV)
Hopefully, one of these movies will work well!
(Remember to test in advance so that you have enough card space and battery duration!)
2) a graph of the luminosity
In this case, my bv_log script measures luminance every about 10 seconds, and (just for reference) shoots a picture every about 10 minutes:
@title Brightness log
rem brightness log
rem reads brightness information every 10 seconds and logs it to pr_screen.txt
rem Plus, shoots a photo every 10 minutes
rem please run with following settings
rem MODE: AUTO
rem flash: off
rem Image size: S (the smallest)
print_screen 1
print "Start Brightness Log"
rem loop counter
p=0
:loop
press "shoot_half"
sleep 1000
get_bv96 B
get_sv96 S
get_av96 A
get_tv96 T
release "shoot_half"
print p,B,S,A,T
if (p%60=0) then shoot
p=p+1
sleep 9000
goto "loop"
If you need more exact timing the script can be changed to be absolutely exact in timing (as long as the camera clock is exact)
This script collects data in a text file called PR_SCREEN.TXT and then you can graph this data easily (for example in excel), obtaining something like this graph: