The control that permits adjustable manual flashes from a 283 is, IIRC, an optional accessory.

And if you are planning to use a 283 with a Canon EOS, it would be prudent to check whether or not it is one of the older ones with high trigger voltages.

Look at this link for more info:

http://www.botzilla.com/photo/strobeVolts.html

Warning: this subject is one of some controversy!