Now some test with a590is fw 1.0.b
- Extra long exposure test with autobuild 778 => OK
- 460 sec. exposure ok, but 470 sec. or more exposure not ok (totally black image, time is ok)
I try generate dark frame(s) with 460 sec. This is difficult. The optical element very weak, do not use any lens cap! I try use "black box", with 10 sec timer, the camera now in the "black box". The dark frame image very bad, very bright, non-usable. I think the problem, the camera own light, the two blinking LED and the black, but not totally black LCD screen. The best method to record dark frame, the canon ring and wide angle converter with own lens cap of wide angle converter. Now the dark frame near ok, only small exposured circle the problem (i think, the canon ring or the wide angle converter not 100% block the external light.
Of course the single dark frame noisy, i see number of hot spot, and have amplifier glow. (possibly the ccd amplifier on/off with CHDK?, amplifier glow strong, but not fatal)
Next i try record set of dark frame, with internal canon function (user timer). The 1. picture recording, the two leds blinking, but if 2. picture recording the two leds not blinking, i think, the camera is freeze, but no, both picture recorded correctly. I not understand. Currently i have not fully processed images to master dark.
I have some test images, if anybody interested, the test picture upload to forum is correct?
Real astrophotography test images not available yet, many night rainy or cloudy.

I try this ugly,and risky script, see under. I want to write the script, with user selectable long exposure time in sec. I not understand, how i do it. I find some information on forum. This script takes 150 sec. = 150* 1 000 000 uSec. image. I think apex2us convert it, but i not know how it. What formula used to convert seconds to this value (-694). Or this script idea bad, more elegant function to control exposure time for this script available?
rem Tested on A590IS
@title Extra Long Exposure - Test
@param a Value
@default a -694
set_tv96_direct a
shoot