How to choose ND filters for the Sony a7R II

There are two parts to this question:

• What ND filters for non-S-Log2 modes?
• What ND filters for S-Log2 modes?

ND Filters for non-Slog-2 modes

The Sony a7R II records video normally in a range of 100 ISO and up (except for Cine4, which starts at 200 ISO).

Here are some general lighting scenarios from real life (Shutter is at 1/50s):

• Sunny 16 rule (bright outdoors) – f/32 @ISO 100, f/2.8 only possible with an ND 2.1 (7 stops) filter
• Studio environment (1000 lux) – f/2.8 @ISO 100
• General office ambience/golden hour – f/2 @ISO 100, f/2.8 @ISO 200
• Moody home ambience – f/1 @ISO 100, f/2.8 @ISO 800

As you can see, you will probably never need more than 8 stops, which is why the following cameras have these built-in ND filters:

• Sony FS7 – 2, 4 and 6 stops
• Canon C300 – 2, 4 and 6 stops
• Arri Amira – 2, 4 and 7 stops
• Arri Alexa XT – 1 to 8 stops

If the aperture isn’t a concern, in bright sunlight, you can get by with a 2-stop filter that will let you shoot at f/16 – which is what most lenses top out at.

Therefore, you can live with ND filters in the 1 to 6-8 stop range. Specific recommendations are in another lesson.

ND Filters for Slog-2 mode

In S-Log2 mode, the lowest ISO is 800. You can’t go to ISO 400 or 200 or whatever. You must start at ISO 800. Here are the same common lighting scenarios and f-stops at ISO 100, and what ISO 800 does to it (shutter is at 1/50s):

We also need to consider the wolfcrow system of exposure, which is to expose at about 2-3 stops over middle grey. If that’s the case, here’s what our chart looks like:

If you want the shallow depth of field aesthetic, you have no choice but to use ND filters. Ideally, you will need a set of 1-10 (0.3 to 3.0) ND filters for video work in S-Log2 mode.

However, most users will be satisfied with 0.3 to 2.4 (8 stops), and it’s extremely rare to hit the brightest part of the day regularly at f/1.4.

How to pick ND filters for S-Log2

There are three ways to go about buying ND filters:

• Buy one or more variable ND filters to cover the entire range. These are circular threaded filters.
• Buy filters in one-stop increments over the entire range. In this case, you’d need 8-10 filters to cover the 8 to 10-stop range.
• Buy four or less filters and then stack filters.

Stacking works like this:

• 0.3 – 1 stop
• 0.6 – 2 stops; 3 stops stacked with above
• 1.2 – 4 stops; 5, 6 and 7 stacked with above
• 2.4 – 8 stops; 9 to 15 stops stacked with above in various combinations

It sounds cool, except for one major drawback – if you stack more than two ND filters, you are likely risking image degradation:

• Internal reflections from various filters
• Vignetting
• Loss of resolution
• If you go above a certain threshold, you risk IR pollution (next lesson)

One way to eliminate these factors is to buy really good filters. The second method is to get them as close as possible to the lens with good quality matte boxes or filter hoods. The last system is to use the right size filter and mattes so vignetting is minimized.

Most cheap filters are made of some form of plastic or resin. The really expensive ones are made of glass. If you stack ND filters and don’t want image degradation, you must stack glass filters.

In any case, it is unadvisable to stack more than two ND filters. I’m going to go with this rule of thumb.

Before I give you my advice, let’s also consider ISO. In many cases, you can bump up the ISO rather than remove ND filters, and this is what lets us stack filters. In our lesson on ISO grouping, we found we can comfortably shoot at ISO 800 (the best) and 1600  in full frame mode, and between 800-6400 in APS-C mode. Here’s what you end up with:

How does this work? What if you need to stop down by one stop only? You ND by 2 stops, and then open the ISO by one stop. Same applies for 4 and 6 stops. ND to a higher number, and then open the ISO by one stop. This way, you can stop down from 1 to 9 stops with just three filters!

If you add one more filter (0.3), you get:

Not only does this give you greater range, but it would allow you to continue shooting at ISO 800 permanently, for best image quality, even using the wolfcrow system.

If you want more versatility, you can add 3.0 to get a full range of 17 stops. I really haven’t come across a situation where I’ve needed more than 10 stops, but also, I rarely open up to 1.4 in daylight.

The best option for the a7R II is to either:

• Buy four filter sizes – 0.3, 0.6, 1.2, 2.1, or
• Buy a variable ND filter that goes from 1 to 8 stops.

In the next lesson, we’ll take a look at IR pollution, so we’ll have a better idea what type of ND filter to buy.