CHDK supports programmatically setting the zoom level on the camera. However, the exact range for the zoom and, apparently, the translation between the zoom level in CHDK and the actual focal length are camera dependent.
In order to figure out the exact range for the zoom and the relation between the numerical zoom steps and the focal length, I’ve used the following Lua script to get the current zoom setting and set it to a certain value. I’ve also configured the camera’s display to show the exact focal length at all times.
-- Guy Rutenberg 2018-08-10
--
--[[
@title Get and Set Zoom
@chdk_version 1.3
@param z Zoom level
@default z 0
--]]
z_old = get_zoom()
print("Current zoom "..z_old)
print("Zooming to "..z)
set_zoom(z)Next, I’ve set the zoom to multiple values and plotted them against the actual focal length. The results are shown in the graph above.
The range for the zoom is 0 to 111, which matches a focal length of 4.5 to 135 mm. The change is pretty linear in two sections: 0 to about 85, and again from 85 up to 111.