| Joined: | Thu Apr 5th, 2012 |
| Location: | St Louis, Missouri USA |
| Posts: | 106 |
| Status: |
Offline
|
There are a few reasons that hot spots can occur, the most common culprit is the matte black coating on the inside of the lens barrel. The coating is designed to absorb stray light from bouncing around within the lens and creating hot spots. Unfortunately this coating may behave the opposite in IR light, instead of absorbing light it may reflect it and end up causing a hot spot.
The other less common reasons for a IR hot spot would be the coatings on the glass lens elements themselves behaving in a way other than what was intended when used in visible light. Sometimes it can also be the interaction of the lens and sensor/micro lenses that causes the light to bounce in a certain way between the surfaces that cause a hot spot.
A large flat rear element would be worse in this regard.
Last edited on Sat Jun 2nd, 2012 07:26 by Dave Groen
____________________
I started out with nothing and still have most of it left