Canon 300 TL - Manual (Page 12)

Zoom Mechanism
24 35 50 85
f
The 300TL offers a zoom mechanism which adjusts the
fiash coverage angle in order to use flash energy more
effectively.
Pull the flash head out and set it to one of the four-click-
stop positions accordingly. A zoom position setting of 24,
35, 50, or 05mm will be illuminated in the indicator on the
back of the flash.
Do not choose a zoom position setting larger than the
focal length of the lens in use.
Lens in-use Zoom setting
24mm 24
35mm 35 or 24
50mm 50. 35 or 24
85mm 85, 50, 35 or 24