baffle telelens (1 Viewer)

I asked this q in camera and photo forum too, but maybe someone here can help.

Is it possible to baffle a telelens like a 300mm f2.8 and get better contrast???
I mean the glass in the lens is round, but the sensor is square, so should be possible to cut out part of the circle with a square baffle.... My 300mm uses these semisquare silicone filters right in the back where the lens mount to cambody - so could make a baffle resembling the filter or no????

Sounds like a waterhouse apeture,which is little more than a perforated washer.By varying size of perforation,different apeture ratios per focal length and diopter of grouping can be achieved.Would require some experimentation so no vignetting would occur.Might help a tiny bit,hard to say.Loss of contrast usually results as extraneous light hits front element,in those cases a hood shaped in same manner as sensor or film plane give best results.Might of noticed squared cornered hoods used on various gear,thats why.Also why use of hood is critical.Some folks increase length of hoods by taping dark paper extensions to lens/hoods that were originally designed for 35mm film and now being used on APS format that topic manifest on. Because of "crop factor"and not using all of image circle as piece was designed for,way back when.