5 pin optical encoder

So I've just found an optical encoder salvaged from a HP printer and I believe it's IR, but the ones I've used had 2 pins for emitter and 4 for receiver, but this one has 3 for receiver. I have attached a few photos of it, maybe someone can figure out how to use it with an Arduino or maybe just the pinout.
Thanks in advance.

The 5th pin goes to the phototransistor's base, can be used to modify collector current for filtering, attenuation, etc.

Thanks, but... how would I connect it to the Arduino?

It's only used in specialized applications, you probably don't need it, just ignore it, it will work just as well.

Looks very similar to me. Maybe you two should connect.