Blackmagic Forum

I am going to purchase the Tiffen 77mm T1 infrared filter but I see that my Tiffen 77mm vari nd does not have front threads. Would it be okay to mount the vari nd in front of the infrared filter, or does it have to be the other way around?

Michael Sharps wrote:I am going to purchase the Tiffen 77mm T1 infrared filter but I see that my Tiffen 77mm vari nd does not have front threads. Would it be okay to mount the vari nd in front of the infrared filter, or does it have to be the other way around?

It does not matter which side an IR Cut filter is placed in the stack. I've tried both sides with a Hoya IR Cut and the GenusTech Eclipse ND Filter.

It does matter if you use a HotMirror IR filter. These filters reflect the light back and you get internal reflections that do horrid things with your image.

Great, thanks Adam!

In a thread I recently created

viewtopic.php?f=2&t=15054

where I posted the results of testing vari nd's with IR pollution one of the readers corrected an erroneous understanding that I had that an ir cut filter was a pure absorption filter. He pointed out (and I have since found evidence supporting it) that an IR cut filter is designed with a dichroic coating, meaning it cuts ir light by reflecting it....in essence it is the same coating as a hot mirror.

This as opposed to an IRND (in Tiffens nomenclature) which is a pure absorption filter, or an IRND +hot mirror combination which I believe is what the schneider IR cut is.

Adam, I have experimented with a hot mirror on the inner stage before a vari nd and when I really ran into problems was when I pointed the camera anywhere toward a light source like the sun or caught reflections off the sun on a gleaming surface.

If, in fact ,your Ir cut has a dichroic coating you may find yourself with unwanted unexpected reflections.

Patrick Finnegan wrote:In a thread I recently created

viewtopic.php?f=2&t=15054

where I posted the results of testing vari nd's with IR pollution one of the readers corrected an erroneous understanding that I had that an ir cut filter was a pure absorption filter. He pointed out (and I have since found evidence supporting it) that an IR cut filter is designed with a dichroic coating, meaning it cuts ir light by reflecting it....in essence it is the same coating as a hot mirror.

This as opposed to an IRND (in Tiffens nomenclature) which is a pure absorption filter, or an IRND +hot mirror combination which I believe is what the schneider IR cut is.

Adam, I have experimented with a hot mirror on the inner stage before a vari nd and when I really ran into problems was when I pointed the camera anywhere toward a light source like the sun or caught reflections off the sun on a gleaming surface.

If, in fact ,your Ir cut has a dichroic coating you may find yourself with unwanted unexpected reflections.

Thanks Patrick

I'll give that another test.

So for $64,000, does the Heliopan Digital Filter use dichroics?

Apparently so:
http://www.amazon.com/Heliopan-707786-77mm-Digital-Filter/dp/B0009KJ048
"This dichroic coated specialty filter..."