Canon EF100-400 IS USM mm lens repair?

[sdwilsonsct]

This lens (bought in 2013) took a dive off the seat when I braked for a dog. The dog is ok, the lens not so much.

Image 1 is a 100% center crop. 30 s exposure on a equatorial mount. I have tried this on different nights and different mounts, and always get fat, oblong stars.

Image 2 is for comparison, same thing with a 70-200 mm f/4.

Is this problem likely to be fixable if I send it away to Canon? Thanks!

[Paul2660]

In my experience fat oblong stars are due to coma.  Did this lens not produce such stars before the drop?,   I guess it's possible the drop misaligned something to produce coma?

Is the lens sharp still at 400 in daylight? 

I really don't think Canon USA is going to be able to fix a coma issue, I base this on my experiences with basic repairs.  They never seem to get much right at least for me and tend to screw up something else, at least on my
24-70, 100-400 and 70-300.  All zooms.  All had issues due to my error, drops, or other issues, but Canon never got them right again.  May have just been my luck.

But coma by design is pretty uncommon in a telephoto lens, much more problematic in wide lenses. 

Paul C

[sdwilsonsct]

Did this lens not produce such stars before the drop?

I guess it's possible the drop misaligned something to produce coma?

Is the lens sharp still at 400 in daylight? 

Thanks, Paul. I shot no stars before the drop, so I don't know.

The lens is reasonably sharp in daylight.

Isn't coma a problem closer to the edge? These are from the center.

[NancyP]

Coma is defined as an off-center aberration, I believe, so it shouldn't be seen in a star at the exact center point. It's possible that there could be some decentering, what with a large number of elements. I would do whatever you do to assess sharpness - shoot a brick wall, or whatever - and see if there is any sharpness problem. No problem in the daytime? Likely it's not decentering that is the problem.

Nice faint fuzzy in the second shot - what is it?

[sdwilsonsct]

Nice faint fuzzy in the second shot - what is it?

Thanks, Nancy. It's M33, here's a stack of 16 (70-200 mm lens). I am gobsmacked by the ability of the 6D to do this.

[Paul2660]

Yes coma is towards the edge. I missed these were center crops.

Paul