I'm doing aerial shoots with a CHDK'd A2200, using USB trigger and the live video feed via a wireless transmitter. I've tried to upgrade to an A4000, I've modified an HTC 11-pin USB connector to fit the Canon
So I had planned to use manual focus at or near infinity, daylight white balance, manual ISO, manual zoom, and Tv set at 1/1000 sec., and then let the camera determine the correct aperture to get the right exposure.
If you know of a script that does the exposure reading, I'd like to look at it.
function check_exposure() press("shoot_half") repeat sleep(50) until get_shooting() == true local tv1=get_tv96() local av1=get_av96() local sv1=get_sv96() local bv1=get_bv96() release("shoot_half") repeat sleep(50) until get_shooting() == false return tv1, av1, sv1, bv1end
tv96, av96, sv96, bv96=check_exposure()if (tv96<752) then tv96=752 sv96=tv96+av96-bv96endset_tv96_direct(tv96)set_av96_direct(av96)set_sv96(sv96)shoot()
if get_nd_present() ~= 0 then set_av96_direct(av96) end
So what appears to happen is that P sets both aperture and shutter speed, but the Auto ISO values in CHDK make it select at least 1/1000 second if it possibly can. But within that limitation, it will set ISO to the lowest value consistent with a middling aperture value (it appears to like f/4 to f/5.6). But if it just can't get a proper exposure at 1/1000, it will open the aperture all the way, set the ISO to maximum, and use whatever shutter speed is needed to get the picture, even if slower than 1/1000. So the 1/1000 is a preference, but not an absolute limit. This seems to work pretty well in limited testing in my back yard, and has a good bit of lattitude.
Maybe better for all cameras:Code: [Select]if get_nd_present() ~= 0 then set_av96_direct(av96) end
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