FYI:
http://en.wikipedia.org/wiki/Atmospheric_refractionWhen air has reletively little turbulence in it, this refraction will be very minimal. As conditions change, so does the clarity of the air.
A photographer/cinematographer can either shoot a scene as planned (such using a long lens through turbulent air or whatever), or instead "shoot around it": If possible re-block the scene and use a shorter lens, or point camera in a different direction, or shoot at a different time of day when conditions may be better, or move to a different location, and so forth.
You can defintely shoot with very long focal length lenses on Blackmagic -- or any camera -- conditions permitting.
John Brawley posted an detailed summary of how he used very long lenses on one of his productions in the BMCuser forum. The link to his post and video examples are here:
http://herefortheweather.wordpress.com/ ... ng-lenses/