IR Contamination/Filter tests - HVX200/RR m2e & nikon - Schneider IRCUT 750

[bmw1602]

I haven't seen much talk around here about IR contamination, there is a ton of it over on the reduser.net forum.

I had to do this test with our RED at work so I brought out my HVX rig and see how it did.......glad I did.

Seeing as we all have 35mm adapters and are seeking a shallow dof, achiving this in the daylight means using various ND filters.

The camera's sensor has a standard IR reflector (aka Hot Mirror) on it. But on a bright day one will typically pile on a lot of ND filtration in front of the lens. Especially when you want a shallow depth of field, after all that's why most people buy a 35mm adapter anyway!

The problem is that standard ND filters block the visible spectrum but not IR. So the effect is to transmit a great deal of IR relative to the visible light, making the IR pollution quite evident. The fix for this is to use a IR reflector (Hot Mirror) in a filter to place in front of the camera lens. Remember, it should always be the first filter in the mattebox so that the IR is reflected out into the world instead of onto the back of another filter.

This will affect different fabrics differently.

So from LEFT to RIGHT. I have SILK-COTTON-NYLON-Polyester.

you will notice COTTON is the most affected while Nylon says black the longest.

ALso a MAJOR factor at play here is the actual DYE in the garment.

This color shift will also affect greens......like grass.

This can be a pain to correct for in POST. In more extreme cases it can almost be not feasable to correct for in post.



SIMPLE FIX.........BUY a IR Filter!!!!!!!!!


Different brands will work better on certain cameras and lenses also have an effect on this.

Tiffen's IR filter reportly works better on the red than the schneider for example.
But any IR filter is better than none.

Fixing this in post is not easy as you might think.


Here a short video of the boring test.
http://vimeo.com/5637250


here some scren shot composites.......(I know, I know I should of been more consistent with my apertures between the before and afters, but you get the point!!!! It's an issue)


Here is the comp sceen shots of the camera with just ND's on it.

Here is the IR version.........

here is a better shot showing each extreme end of the contamination spectrum.

Here is a DIRECT comparison of BEFORE and AFTER the use of a IR filter

ANYWAYS........the conclusion is obvious.........use a freakin IR filter.

Like I said IR contamination also affects other colors!!

 

[Ryan Patrick O'Hara]

Fantastic tests!
Thank you for sharing this!

How I try to avoid this issue, (when using a 35mm adapter) is to use the camera body's Iris. I close it down to a health f/8 before I move onto ND's.

Your work is much appreciated!

 

[Lenilenapi]

Having done quite a bit of testing of IR issues on the Ex-1 with Art Adams, I am concerned about critical missing information in these tests.

Most important
- what brand of ND filters were you using. There is tremendous variability here between different brands of ND. Some cut IR (or far Red which is often the problem more than actual IR) quite well and others don't. You can often see this with the naked eye. Hold your ND up over various black fabrics and some will obviously turn your fabrics red.
In my experience for example Schneiders ND filters were quite bad in this regard, Tiffens were not as bad but still had problems. On the other hand my own B+W and Heliopans had no IR/far Red issues at all.

- Did you try the internal HVX200 ND filters? In many cases I have found the internal ND filters of most cameras handle the IR problem quite well and there is no need for additional IR cut filters. Even on the EX-1 which is very sensitive to Far-Red the internal ND filters do not seem to contribute to the problem at all. I don't recall testing the HVX internal ND's, but its possible that if you stick with those you may have no problems.

ND issues with IR and Far Red seem to have slid under the radar for a long time and many of these problems have been with us for quite a awhile. The only way to know about your own camera and filters is to test them yourself.

My experience is also that it is not at all true that any IR filter is better than none. Unfortunately IR and Far Red cut filters are also all quite different and which one is appropriate to your camera is also confusing, since the sensitivity issues of different cameras are also all over the map. Some of the most effective will vignette green on wide angle shots. The best info about this is on Art Adams blogs on the provideocoalition.com website.

Lenny Levy