Hola,
Respecto al Samyang 21 1.4 lo cierto es que hay poca información, he buscado en la web de
Lonely Speck (muy recomendable) que tiene varias reviews de los Samyang y algo dice, y parece ser una buena opción para astrofotografía
In this article I talk about our favorite gear, some of which has helped shape our world of landscape astrophotography. Check out what we’re looking to buy this holiday season and why.
www.lonelyspeck.com
"The
Rokinon 21mm f/1.4 is the most affordable, fast 21mm lens available on the market. It’s specifically cited by the manufacturer as having excellent coma performance which should make it perfect for astrophotography. It was just released and at the time of this writing, have not gotten to use it but it’s the
most voted upon lens for us to review. Photographers using APS-C mirrorless cameras that want a lens that mimics the field of view and light gathering capability of a full frame 28mm f/2 lens (like the Sony 28mm f/2 that we love so much) should get the Rokinon 21mm f/1.4. Like the 12mm/2 mentioned above, there isn’t really anything directly comparable to it for APS-C mirrorless cameras."
Saludos!