BY PAWEL ACHTEL: www.achtel.com A pro's perspective on common misperceptions regarding Pancro IR+ND Filters

"I always support good products and superior solutions and have no problem to do so with Pancro mirrors."

"I really appreciate the superiority of Pancros solution on technical merits. It is the best I found. "

Pawel

 I think it is important to demist some misconceptions, such as:

 1) It is camera's deficiency-

 it is not, it is always a technically superior solution to filter out IR before the lens than after it.

2)Dichroic filters are better. Where as, they are not. The nature of a dichroic coating is that off axis performance will always be compromised because the wavelength that is filtered at an angle will be longer than that in the centre. Thus, dichroic filters will always exhibit colour shift off axis. Either that, or they would pass significant IR in the centre.

3)I don't need to use mattes.

Where as it is absolutely critical to cut off any stray light falling onto optical elements of the lens as any reflection off the optical element in the lens will bounce back from the IRND mirror and cause ghosting.

I can't see any problem in my monitor so I don't need IRND. Where as IR will almost always contaminate the image above ND .6 and this contamination can be seen on a large screen or good evaluation monitor. This is not just a feature of RED One. All cameras I tried, including Canon DSLRs suffer from IR contamination under most conditions where ND .9 or stronger is used. One exception is underwater, where there is no IR at all.

4)I can stack IR ND filters. 

Where as, you can not. There can be one and only one reflective filter in the optical path and it is always the outermost. Additionally, no other dichroic filters can be used at the same time.

5)IR contamination only shows up on black nylon or green foliage.

Where as, it also shows up just about everywhere and demonstrates itself in fuzzy edges and lower contrast.

6)It doesn't matter which side out the IR ND is facing.

Where as it does, It has to face the reflective side out to further eliminate reflections off the non-reflective side back to the mirror.

7)Any IR ND filter will do. Where as both practical tests as well as theory shows that only broad spectrum mirrors (thin metal deposit) are the only currently known solution that does not change off-axis performance and preserve colour balance. Other types of filters will almost certainly cause problems in wide angle situations, no ifs or buts. That's the principle how they work as there is no known IR absorbing material that would have sharp cutoff and flat transparency curve in the visible spectrum. And, dichroic filters always suffer from off axis shift.

8)I can use IR ND mirror on any lens. Where as some lenses have highly reflective coatings and may cause internal reflection off the filter. Use good lenses, such as Red, modern Cooke or Zeiss  no problems there. Some old beaten glass may not have the type of optical quality (transparency) needed for compatibility with mirror-type filters. It is an important consideration when choosing a lens. In my experience, Arri-Zeiss Master Primes as well as Red 300mm prime are perfect for using mirror-type filters and I found no side effects even in the most difficult lighting conditions.