Is there an addon, or an easy way to add lens flare effects or light aberrations in Blender? I've been using Blender for a while now, and it's very time consuming to always have to export to another software to do them, and sometimes it's impossible if the scene is complex.
There is an OSL lens-flare shader by iReboot (aka Dylan Whiteman) which may interest you.
From his blog post referring to a lens-flare shader originally written for the Renderman language by
Larry Gritz & Tony Apodaca of pixar, iReboot writes:
I decided to try and port this to OSL - (...) I added a few features, such as user definable images for lens-flare elements and have got to a point where the shader can now be released.(...) - along with video tutorial links
In addition to the OSL shader mentioned by zeffi, you can try these:
Blender Internal(2.79 or less) only:
You can use the Halo material with the Flare option enabled to fake lens flares.
Cycles and BI:
Using Compositing nodes:
You can use a Glare node set to Ghosts to make a lens flair.
For chromatic aberration, you could use a Lens Distortion node with the Dispersion value set to something greater than zero.