What are Hot Mirror filter for?

[marvelous1200]

Hello range finder forum-ites, this is my first post although i have been coming to this site for a while now. some great threads on here. Hopefully some of you can help me with this question.

I just came across some Tiffen Hot Mirror Filters at my job. what exactly do these filters do. I understand that they block IR light, but I'm not sure what exactly that means image-wise. I usually keep a UV filter over my lenses for protection, but my UV filters are gettin old and these are crispy clean. I shoot velvia, Tri-x and Pan-F 50. will i notice a difference if i use these filters or not? If not thats fine because more than anything they can just be protection for my lenses. but if they do have an effect i would like to know about it.

thanks in advance

 

[AndyPiper]

As you say, they block infrared - a big deal for Leica M8 users (and to some extent for Epson RD-1 users). Digital sensors are sensitive to IR and give screwy colors unless it is blocked. (Search "M8" and "magenta" here at RFF)

For your film work, they will have one downside - green corners to your color shots with wideangles (also an M8 issue). Take one of the filters and turn it back and forth so that you are looking through it slantwise, and you will see that it gets increasingly green/cyan in color as you look through it at more and more of an angle (as a WA lens would do).

In effect the filters start filtering visible red light as well as invisible "red" IR at those steep angles. In B&W shots this may show as slight darkening in the corners, since you're starting to affect visible light.

The other downside is the flip side - literally. The filters usually reflect a bright red when seen from the side when mounted on a lens, which makes your camera stand out like a traffic light. Not good if you're trying to remain invisible.

But try them, and see what effects there are, and how strong.

And don't bother using infrared film behind them... 8^)