I'm planning to buy a 200-250 mm lens for doing astrophotography with my trusty autoguided Vixen GP. My camera is a Canon T3i modified. Bortle sky: 3
What of the three options would you choose for the task and why your election?
REDCAT: 250mm f/4.9. Petzval design but some reports of a slight coma in the corners.
Askar ACL200: 200 mm f/4. Sextuplet design in 3 groups. Very hard to find documentation or reviews of this lens.
Canon 200 f/2.8. Coma in the corners but very high speed.
What's your choice?