East Grinstead photographer and filmmaker Nitsan Simantov. Wedding photography and commercial video production in London and West Sussex.

Sony A7S internal ND filter (Reduces moire too!?)

[WARNING: Incorrect usage could damage your camera. Do not put the filter in the way of the shutter. Do not touch the glass covering the sensor.]

Some shooters have used ND filters internally, usually when there is no filter thread on the front of the lens, but for me an internal filter is used for another reason, because front-mount filters often give me some nasty reflections when working with strong back lighting or strong highlights in the shot, no matter how expensive they are, and the second reason that the A7s has such a hard time recording videos in daylight that it may need two ND filters to get the correct exposure.
The reason for that is that the Sony has to be at or above ISO 3200 to get it's highest dynamic range in video, which is done using the S-Log Picture Profile, called PP7. "S-Log" is basically a color profile that was made to get largest amount of color and tone data within a compressed image, sort of like the flat 'Picture Styles' we use on Canon cameras, just far better.

So this means if I want to shoot videos at an f1.4 aperture and 1/50th shutter speed in daylight using PP7 I am pretty much have to use one or more ND filters, but the problem is that filters in front of the glass can very often cause incredibly ugly reflections if there are very bright areas in the image. I am not sure if every photographic filter does that but all the ones that i have used so far do, and I anyways do not have the budget to buy expensive filters at the moment.

My solution for now is to use an internal filter. I ordered a 0.9 ND gel filter (intended for lighting) from eBay for £1.50 and specifically asked the seller to send me a nice clean piece (which they certainly did, even wrapped perfectly in soft paper) and it so far works beautifully to lower my exposure by 3 stops. The piece is so large that I could easily cut a lifetime supply of filters out of it, so I don't need to worry about ruining or losing one. It's also nice that it gives an extra layer of protection to the sensor.

Link to the seller I bought this filter from.

This is my first one, slightly damaged and not sitting fully straight in the camera, but there is actually a PERFECT slot just in front of the shutter that holds a gel beautifully in place in all directions. I just didn't have time to make another filter today. Make sure you leave a little tab in the filter so you have something to grab onto to remove it. it sits so well in the slot that it is hard to remove without a little pull tab. I'll post some more photos soon. As you can see below there is no noticeable difference, except the noise due to the ISO difference in the two images.

Click image for larger view. Shot on the Samyang 35mm at f8.

This is a 100% crop from a 12 megapixel image, so a 1080p image (2MP) and 4K image (8MP) should be affected even less. Notice how the filter removed the moire (false color) in the small details on that Pixapro light on the left side of the table - a brilliant little unexpected advantage. I will try some video in crop mode (that's where the A7S has a tiny bit of moire) and post an update below.

Even though this could be very helpful for a few specific uses when stills shooting, it's really intended for video, because when shooting stills mode the PP7 mode is absolutely not needed (just shoot raw) so you can go down to ISO 100, and in stills you can control the exposure with the shutter speed too, which you cannot do in video if you want smooth motion. Of course there is also the aperture, but in both cases we are assuming you want the option for shallow depth of field when shooting in daylight.

I have also tried to double up the gel to reduce the brightness further (Yes, it will absolutely be needed in some situations) and it worked really well, but the test below was just with the one filter. But if anyone knows where to find a really dark ND gel, please let me know.


Some people are not carefully reading the article and are messaging me on Facebook asking "why not use a screw-on filter" and similar questions, so lets go over the highlights quickly:

  • Most importantly, FAR less ugly reflections than glass adapters, which is the main reason for doing this, as I explained above.
  • Cheap.
  • Easier lens changes.
  • Possible moire reduction.
  • No loss of quality as far as I can see.
  • Less to carry than normal filters.
  • Should work with all lenses and adapters, so you can still use your Lens Turbos, Speed Boosters, helicoid (focusing) adapters, unadapted lenses from Sony or lenses with small adapters like my Leica M mount Voightlander 35mm f1.4 - None of this is doable with the lens adapters that have built-in ND filters.
  • Protects the sensor. Might even mean you never need to clean the sensor, since the dust will land on the filter, which is far easier to clean or even just replace. If you get a few specs of dust, it should be less visible because it is far from the sensor.
  • Should be usable with lenses that have no screw thread for filters (such as most super-wide-angle lenses)
  • If you make a pull-tab on the gel then it's just as easy to remove as a regular glass filter. Remove the lens, grab the pull-tab and pull out the filter, put the lens back on, then place the gel in a safe place, or just chuck it in your pocket, it's so cheap that it doesn't even matter if you ruin it.
  • So far no autofocus issues in both video or stills modes.
Link to the seller I bought this filter from.

Update 2:

Here is a video I shot with two of these ND filters in the camera:

[WARNING: Incorrect usage could damage your camera. Do not put the filter in the way of the shutter. Do not touch the glass covering the sensor.]