Over the last 2 weeks I have been shooting some tests for a major feature film. The tests involved a special process that involves the use of Infrared light and shooting outdoors.
On the test day we had some fairly bright light levels to deal with. So as you would normally do we added some ND filtration to reduce the light levels. Most of the equipment for the shoot was on hire from Panavision, the main cameras being Panavised Sony Venices with PV70 mounts and Panavison lenses. But for reasons I can’t go into yet, we were unable to use the Venice internal ND filters, so we had to use external ND’s.
The first ND’s we used were circular Tiffen IRND’s that were the correct size for the PV lenses. But much to my surprise these made very little difference to the amount of IR reaching the camera. For our application they were absolutely no good. Fortunately, I had a set of Formatt Hitech IRND’s in my camera bag and when we tried these we got an equal visible and infrared cut. So, the Tiffen’s were put back in their boxes and the Formatt filters used instead.
Back at Panavision we did some further testing and found that both the Tiffen and Schnieder IRND’s that we tested had very little IR cut. But the Formatt Hitech and Panavision IRND’s that we tested cut the IR by a very similar amount to the visible light. In addition we were able to test the Venice built in ND filters and found that these too did a very good job at cutting both IR and visible light by similar amounts.
So, my recommendation is – if you are ever concerned about infrared light contaminating your images use a Venice 2 with it’s built in ND’s, Panavision or Formatt Hitech IRND’s.
Tag Archives: ND
Handy Tips For Using The Sony Variable ND Filter Values.
Sony rate the ND filters in most of there cameras using a fractional value such as 1/4, 1/16, 1/64 etc.
These values represent the amount of light that can pass through the filter, so a 1/4 ND lets 1/4 of the light through. 1/4 is the equivalent to 2 stops ( 1 stop = half, 2 stops = 1/4, 3 stops = 1/8, 4 stops = 1/16, 5 stops = 1/32, 6 stops = 1/64, 7 stops = 1/128).
These fractional values are actually quite easy to work with in conjunction with the cameras ISO rating.
If you want to quickly figure out what ISO value to put into a light meter to discover the aperture/shutter needed when using the camera with the built in ND filters, simply take the cameras ISO rating and multiply it by the ND value. So 800 ISO with 1/4 ND becomes 800 x 1/4 = 200 (or you can do the maths as 800 ÷ 4). Put 200 in the light meter and it will tell what aperture to use for your chosen shutter speed.
If you want to figure out how much ND to use to get an equivalent overall ISO rating (camera ISO and ND combined) you take the ISO of the camera and divide by the ISO you want and this gives you a value “x” which is the fraction in 1/x. So if you want 3200 ISO then take the base of 12800 and divide by 3200 which gives 4, so you want 1/4 ND at 12800.
Setting The White Balance When Using The Variable ND Filter
It’s no secret that the variable ND fitted to many Sony cameras does introduce a colour shift that changes depending on how much ND you use. But the cameras are setup to add an offset to the WB as you switch the ND in or out and change the amount of ND, so in practice most people are completely unaware of this shift.
If you watch carefully when you engage or disengage the ND you can sometimes see a fraction of a second where the cameras electronic offset that corrects for the shift is applied just as the filter comes in. Then once the filter is in place the colours appear completely normal again.
So when should you white balance from a white card? With or without the ND filter in place?
You can actually white balance either with or without the ND in place. Because the camera knows exactly what offset to apply for any ND value if you change the ND it will compensate automatically and generally the compensation is very accurate. So in most cases it doesn’t really matter whether the ND filter is in place or not.
You can actually white balance either with or without the ND in place. Because the camera knows exactly what offset to apply for any ND value if you change the ND it will compensate automatically and generally the compensation is very accurate. So in most cases it doesn’t really matter whether the ND filter is in place or not.
However, my personal recommendation is where possible to white balance with the camera setup as it will be when you are taking your footage. This should then eliminate any small errors or differences that may creep in if you do change the ND or switch the ND in or out.
But I wouldn’t be too concerned if you do have to do a WB at one ND level and then change the ND for whatever reason. The in camera compensation is extremely good and you would only ever really be able to see any difference if you start doing careful like for like, side by side, split screen direct comparisons. It’s certainly highly unlikely that you or your audience would ever notice any difference in normal real world applications.
You will often see greater colour shifts if you add external ND filters or swap between different lenses, so treat the internal ND as you would any other ND filter and WB with your lens, filters and everything else as it will be when taking the footage. I think one of the truly remarkable things about the variable ND filter is just how consistent the output of the camera is across such a wide range of ND.