NavList:

It might help to illuminate the entire field with some background light---that way the overall contrast of the scene would be reduced, so that the eye would see just the bright cores of the stars against a grey background.  Start with no light, acquire the blobs in the field of view, then gradually turn up the light source until the stars are maximally pointlike, but not so much that they're not easily trackable by eye as the sextant is swung and adjusted.

The few times I've looked at Venus during the day with binoculars, I've been struck with how pointlike it seems against the blue sky.

I have some camera images of star-star sights---they don't show the "fuzzy blobs" problem provided the exposure doesn't saturate the stars.  At some point I hope to finish the job of estimating my sextant's arc error using these images.

Cheers,
Peter