Data sheet is at: http://www.prolight.co.uk/ftp-in/LEDJ252D_Manual.pdf
I've set the Zoom channel to [0-255]: Zoom (Big to small) since Ledj confirmed:
The zoom plate at value 000 is at 75 deg – at value 255 zoom plate at 25 deg – hope this helps
Kind Regards, The Prolight Concepts Group, Mick, Technical Department Manager.