or that some work in 1/8th stop (12 unit) steps.
Looks like my entire lens has 12 unit step (with the exception of the beginning).
Here is another run with step size 1 with
EF 24mm f/2.8 IS USM
EF-S 55-250mm f/4-5.6 IS STM at 55mm
EF-S 10-18mm/f4.5-5.6 EF-S IS STM at 10mm
It would be nice for CHDK to be able to know which stops are valid.
Yes of course…
Edit:
Never mind, I see you are using CHDK build 4928. The min / max Av functions were added in 4998. The error you get is that the function itself is nil.
Ups, still used a test version from lapser

. Update done…
I tested my entire lens with the following Script:
press'shoot_half'
repeat sleep(10) until get_shooting()
local AV96=get_prop(props.AV)
release'shoot_half'
print_screen(get_day_seconds()/10)
local dof=get_dofinfo()
print("AV Values")
print(' FL=',dof.focal_length)
print(' AV96=',AV96,',f',fmt_av(AV96))
print('Min AV96=',get_min_av96(),',f',fmt_av(get_min_av96()))
print('Max AV96=',get_max_av96(),',f',fmt_av(get_max_av96()))
On some lenses I got smaller AV96 values with get_prop(props.AV) as with get_min_av96 like:
EF 24mm f/2.8 AV96=288 (what I expect) and Min AV96=300
or
EF-S 55-250mm f/4-5.6 IS STM at 55mm AV96= 384 (what I expect) and Min AV96= 396
Interesting on both lens:
Min AV96 on this lens is exactly 12 stops before the first real aperture change.
Here are complete results:
EF 24mm f/2.8 IS USM
AV96= 288 ,f 2.82
Min AV96= 300 ,f 2.95
Max AV96= 876 ,f 23.62
EF 50mm f1.8 USM
AV96= 168 ,f 1.83
Min AV96= 168 ,f 1.83
Max AV96= 864 ,f 22.62
EF-M 15-45mm f3.5-6.3 IS STM at 15mm
AV96= 348 ,f 3.51
Min AV96= 348 ,f 3.51
Max AV96= 864 ,f 22.62
EF-M 15-45mm f3.5-6.3 IS STM at 45mm
AV96= 516 ,f 6.44
Min AV96= 516 ,f 6.44
Max AV96= 1032 ,f -24.-3
EF-S 55-250mm f/4-5.6 IS STM at 55mm
AV96= 384 ,f 4.00
Min AV96= 396 ,f 4.17
Max AV96= 876 ,f 23.62
EF-S 55-250mm f/4-5.6 IS STM at 250mm
AV96= 480 ,f 5.65
Min AV96= 492 ,f 5.90
Max AV96= 972 ,f -32.-11
EF-S 10-18mm/f4.5-5.6 EF-S IS STM at 10mm
AV96= 420 ,f 4.55
Min AV96= 420 ,f 4.55
Max AV96= 864 ,f 22.62
EF-S 10-18mm/f4.5-5.6 EF-S IS STM at 18mm
AV96= 480 ,f 5.65
Min AV96= 480 ,f 5.65
Max AV96= 924 ,f 28.10
The CHDK C implementation should be correct, and should work for anything over f/1.0. We should probably support f/1.0 and below now that we have ILC cameras...
Looks like av96_to_aperture has problem with high AV96 values like 972. If I understand shooting_get_aperture_from_av96 correct, then the function returns an unsigned short and this is limited to +32.767.
972 deliver 33417.