Rotary table DRO

Hello,

I was wondering if someone may be able to help me with a problem I
have at the moment.
I am trying to add a DRO to my 'little' rotary table. It is 6 meter
diameter. I am looking to get .05mm accuracy if at all possible. I
was thinking of puting a rotary encoder onto the main spindle which
is coupled directly to the table, but to get the resolution I am
looking for I need approx 400 000 pulses per rev (0.00095 deg). All
the encoders I have looked at seem to be about 8000 pulses per rev in
quad. Is it possible to gear an encoder up? If so how (so as to get
minimal backlash)?

Thanks for your help
Andrew