Lens aberations, star shapes and tracking

[Albastars]

I was out last night, not expecting great images because of the moon, but testing my setup - Fornax Lightrack II and Sony A7riii plus 100-400mm lens at 400mm.  With my best Polar alignment yet, I managed my first reasonable 3min sub but, to be honest, I was hoping for better.  When viewed at 100% there isn't much difference between the 2 and 3min subs but there is clear trailing at 4min.  Can anyone comment on whether I should be able to get 4mins at 400mm?  Or maybe I should refrain from pixel peeping?

Its noticeable in all the subs below that the smaller stars have the appearance oh 1/2 moons with Earthshine.  Can anyone explain what this is?  Some kind of lens aberration I guess?  My zoom lens is a quality bit of glass but it wasn't designed for AP but its all I have at the moment.  My plan is to push this lens as far as I can on the Fornax and from there decide on a telescope.

I went on to take 78 1min subs of the Hercules Globular Cluster (no calibration frames) just for fun but and with no great expectations. 

 

 

[Icesheet]

Can’t really comment on lens aberrations but I’m curious about the tracking you’re getting with the Fornax. I agree, looks like you’re getting good tracking at 3mins at 400mm. That’s pretty amazing unguided. Are you happy with the mount?