You can make the aperture seem bigger if you shorten the optical level arm.
 That is use one less set of mirrors to shortent the beam path on the
detection side by 1/2
 
The eyepiece is adjusted in position so that the scanning mirrors are at
the telencentric (fourier) point in the optical path.  At this site, angle
of the light beam directly dictates position in the specimen plane.
Therefore the galvo mirrors scan the specimen by changing the angle that
the light passes. Among other things, misadjustment will overfill the back
aperture in a way that changes with phase in the scan cycle so you'll see
image intensity falling off away from the center.
 
 
 
Scott Fraser  ([log in to unmask])
Caltech, Beckman Institute (139-74)
Pasadena,  CA  91125
818 395-2790 telephone
818 449-5163 fax