As a result of many questions coming my way via social media I decided to create this back to basics primer article on ND filters for mirrorless cameras.

01. Sometimes I use ND just to get away from f/22 or f/16 in order to get down to f/8 when I’m working with flash on sunny days. I used an old Hoya NDx4 with my XF 60mm lens on an X-Pro1 for this flashed shot in Spain. I lit Natalia with a pair of Canon 580EX2 Speedlights on full power into a small 40cm silver brolly attached to a boom arm above and in front of the sign.

The Mirrorless advantage

Whatever camera or lens combination is used when working with big flash systems including studio flash or Elinchrom Quadra it is stuck at the maximum flash shutter sync speed. However mirrorless camera owners can use ND filters to allow the lens aperture to open up accordingly without affecting their view of the shot. This is purely for artistic considerations to create background blur. Put a 9 stop ND filter on an SLR and it’s nearly impossible to see the shot for composition and the AF system is unlikely to work either. Electronic viewfinders on mirrorless cameras compensate for the filter and show you the picture in real time. This system works for Speedlights too so when shooting with a Speedlight on a mirrorless system, ND filters can be used to allow the lens to be set at a wide aperture. On SLRs high speed sync is the way to go.

02. I used Hoya PROND8 on this simple shot of Victoria to keep my 56mm lens wide open at f/1.2 when shooting with flash and a shutter speed of 1/180th second.

01. On the left is the exposure cut required and in the fourth column the corresponding Hoya Pro ND filter code. There are many other makes of ND filters but I have found the Hoya Pro range to be superb.

Those pesky little f numbers might seem quite random but they have managed to keep their place in modern day photography along with the 1/4″ (inch) British Standard Whitworth thread in the bottom of every camera. The good news is you don’t need to calculate f numbers, just establish how many stops there are from one to another.

There is a relationship in the f numbers that I use to determine the amount of difference needed with ND filters. This tells me there are 4 stops from f/16 to f/4 and 6 stops from f/16 to f/2 etc.

The f numbers relationship is quite straightforward once you realise every other value is double or half. So double f/2 is f/4, that’s two stops and double again to f/8 makes four stops and double again to f/16 makes six stops in total from f/2 to f/16. The same is true for f1.4 to f/2.8 being two stops etc but at f/11.2 they decided to drop the .2 bit. It makes it simpler to calculate and that’s a good thing.

On Fuji lenses with f/number markings on the aperture ring it is easy to count the stops but on other makes of cameras and lenses you will need to calculate the value of ND required. You can count clicks with each click being ⅓rd of a stop or use my system above.

03. I shot this frame in full sun with a Cactus RF60 Speedlight on a boom arm above the camera. I set my lens to f/1.2 and my shutter speed to 1/180th. I was on ISO 200 and used a PROND8 combined with a PROND64 to give me 9 stops of effective reduction. The viewfinder image was perfect.

What filter values do I need?

You can calculate what filters you will need with the help of the chart above. I use Hoya filters and chose to use PROND8, PROND16 and PROND64 plus I have a PROND1000 for long exposure effects and a PRO1D CIRCULAR PL polarising filter. The polariser cuts the light by about a stop. I use the filters one or two at a time to make up the values I need.

With these three ND filters and a polariser I can get 1, 3,4,5,6,7,10, 13,14 and 16 stops of light attenuation by using either one or two filters at a time. This covers all my needs. I don’t mind bumping the ISO up to 400 if needs be too from time to time.

Do I need filters for all my lenses?

No, reducing depth of field with wide lenses is far less effective so I tend to just have sets for my telephoto and standard lenses. A polariser is a good filter to use on wide lenses when shooting with flash in bright sunny conditions because it will keep the lens away from the dreaded f/22. The sweet zone on nearly all mirrorless lenses is f/2.8 to f/11. Go above f/11 and the quality of the image begins to fall away because of aperture diffraction. As a rule of thumb the faster the lens the earlier the diffraction sets in. On lenses with a maximum aperture of f/1.2 it is common to have a minimum aperture of f/16 while f/2.8 lenses often have f/32 as their smallest aperture.

Whatever system you use, get creative and stay inspired.