If you have a capable camera and a modern telephoto lens of 300mm or longer, you have two potent tools, that can
produce arresting images of everything from landscapes to sports, to portraits and more. What you may not know is that

these tools can also open the door to another exciting dimension in your photography!

The photography of fast flying objects...fast birds, planes and even insects, close up! You'll find these nearby subjects

packed with detail, and the longer the lens, generally, the more so!  Sounds great, but naturally, there's a catch....longer lenses

have very small fields of view, making fast target capture and tracking very difficult.
A Full Frame camera, using a 600m lens on a target 50ft distant, 16x9 format, will offer an FOV of roughly 38"x 21"or 96 x 54cm.

A very small window in which to capture and hold a fast moving and maybe erratic target. If you're using a crop sensor camera,

then this window will be smaller still.
This is where a Red dot, or Reflex sight system comes in. It frees you and your photography from the tiny  VF window. 
Instead you see the whole sky and everything in it, your target included. All you have to do, is point the Red dot at the target,

press the shutter button, and create a stream of images....
Thus, the almost impossible becomes almost too easy!