Falling well within the “budget lens” category is the Rokinon 85mm F/1.4 AS IF UMC lens ($299 new at the time of this writing). Below are some evaluation images I shot using this lens on a Canon EOS 6D. A Hoya Intensifier filter was also used to help lessen the light pollution effects of the red zone I live in.
The following mosaics were made from 100% crops using light frames shot on a Canon EOS 6D body (unmodified) at ISO1600 from a red zone. Exposure times started at 2 seconds at F/1.4 and doubled with each successive aperture stop. A Hoya Intensifier LPS filter was used to reduce the effects of light pollution. Use the gallery below to cycle through light frames gathered at different apertures (click to view full-sized images).
The Rokinon 85mm F/1.4 AS IF USM lens exhibits reasonably good corner/edge performance at f/2.8 and above. Coma is still an issue at F/2.8 in the Full-Frame edges, and astigmatism is always present in the far Full-Frame corners. Chromatic aberration is pretty harsh until F/4.0 and mostly gone by F/5.6. It’s probably best if this lens is stopped down to F/4.0, and perhaps better on an APS-C body.
Vignetting is very strong at F/1.4 but improves at F/2.0 and is much better at F/2.8 and higher. These images were shot using the same body and settings as the light frames above.
Figure 1: Deneb shines left of center in front of several emission nebulae, including Gamma Cygni, North American, and the Pelican Nebula. Unmodified Canon EOS 6D, ISO1600, F/4, 60x60sec calibrated stack. Prints available.
Figure 2: Orion and Monoceros region, Canon EOS 6D, ISO1600, f/2.8, 29x120sec calibrated stack. Prints available.