200mm Lens Shootout for Astrophotography

If you are at all interested in astrophotography, you may have wondered if your current lenses are up to the task of capturing sharp, distortion-free images of the stars. Something most modern digital lenses weren’t intended for.
By now everyone has heard of the superiority of the Rokinon brand. And while these lenses do have their pedigree in astrophotography, the bulk of the fanfare these lenses have garnered has been in their wide-angle products. What if you wanted a narrower field of view for closeups of larger nebulae?

In this video by Nico Carver, also known on YouTube as Nebula Photos, does a comparison between the Canon 200mm f/2.8 II, and the Askar ACL200 f/4, which is a purpose-built astrophotography lens. On paper, the Canon seems to have the advantage with things like autofocus, a wider maximum aperture, and significantly lighter weight. But when he compares their performance after shooting the night sky, the Askar makes a compelling case. Things like chromatic aberrations, field curvature distortions, and vignetting usually plague digital camera lenses when pointed up at the stars. And it seems like the Canon is no exception here either, having extremely visible chromatic aberrations throughout the field. Carver then goes on to compare how one would use these lenses with other astrophotography accessories, and the merits and shortcomings of both. 

All in all, the Askar ACL200 f/4 is an interesting option for more narrow-field imaging of the night sky. I for one am constantly disappointed in my Canon 70-200mm f/2.8 II for astrophotography, as I am troubled by the same weaknesses he shows from the Canon 200mm prime. When shooting at f/2.8 I get bloated stars with wicked chromatic aberration and vignetting, made worse by unappealing diffraction spikes when stopped down to compensate. Autofocus is useless on stars, and the travel on any focus ring is so minute that it's extremely frustrating to acquire focus and keep it. The biggest reason people may stay away from the Askar, is that it's not dual purpose. If you already own a 200mm prime, regardless of the manufacturer, you might be willing to put up with some of its shortcomings if indeed they even exist. After all, you can still use it for the intended purpose by pointing it back down to something here on Earth.

Keep in mind that the Askar ACL200 f/4 is compatible with any camera, so long as you provide the correct adapter.