In Part Three we covered cine and zoom lenses for the Sony A7s. In this part we’ll look at:

  • Filters
  • Internal Recording

 

Filters for the Sony A7s

To know more about camera filters and when to use them, read the Complete Guide to Lens Filters.

ND Filters

The Sony A7s records 1080p video in Rec. 709 under an ISO range of 200-102400 (expandable to 409,600). However, in S-Log2 mode (more later), the lowest ISO is 3200. You can’t go to ISO 1600 or 800 or 400 or whatever. You must start at ISO 3200. Here are some common lighting scenarios and f-stops at ISO 100, and what ISO 3200 does to it (Shutter is at 1/50s):

  • Sunny 16 rule (bright outdoors) – f/32 @ISO 100, f/196 @ ISO 3200 (which is impossible. Even f/32 is rarely found on 35mm lenses, if at all)
  • Studio environment (1000 lux) – f/2.8 @ISO 100, f/16 @ISO 3200
  • General office ambience/golden hour – f/2 @ISO 100, f/11 @ISO 3200
  • Moody home ambience – f/1 @ISO 100, f/5.6 @ISO 3200

 
As you can see, the low light ability of this camera is phenomenal. However, if you want the shallow depth of field aesthetic, you have no choice but to use ND filters. But there’s a huge problem.

Because exterior and interior lighting levels vary, you’ll be forced to consider a large range of ND stops (which usually come in one-stop increments). One way to reduce the number of ND filters involved is to stack them, like this for example:

  • 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
  • 4.8 – 16 stops; 17-31 stops stacked

 
It sounds cool, except for one major drawback – if you stack more than two ND filters (two is pushing it), you are likely to create serious and visible image degradation:

  • Internal reflections from various filters
  • Vignetting
  • Loss of resolution

 
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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. If you go by this rule, you’ll need about 5 ND filters to cover a range of 15 stops. In the sunny-16 rule mentioned above, if you want to shoot at f/5.6 @ISO 3200, you’ll need an ND of 10 stops. If you want shallow DOF at f/2, you’ll need 13 stops. Therefore, while shooting with the Sony A7S, I recommend you carry a 10-stop range worth of ND, at least.

Here’s what you might want to use:

Assuming you absolutely have to shoot at the rated ISO of 3200

Optical Density Stops Stops you get by stacking Approx Price (77mm) Approx Price (4×4)
0.3 1 1 $43 $120
0.6 2 3 $23 $120
0.9 3 4,5 $43 $120
1.8 6 7,8,9 $89 $140
3.0 10 11,12,13,16 $83 $140
Total $281 $640

Notes:

  • I’ve used Tiffen and Lee as references, because they are relatively cheaper.
  • Lee does not make filters in the same stop range as the above list. Some are just approximations.
  • I’ve taken 77mm as the base because in Part Two I chose Nikon primes, of which the greatest filter diameter is 77mm. For the others, I’d use step-down rings.
  • Prices and specifications may be inaccurate or unavailable. Please refer to manufacturers’ websites for correct information.
  • These notes apply to the next two charts as well.

 
Assuming ISO 6400 is as good as ISO 3200

Optical Density Stops Stops you get by stacking Approx Price (77mm) Approx Price (4×4)
0.6 2 2 $23 $120
1.2 4 6 $43 $120
2.1 7 9,11 $89 $140
3.0 10 12,14,18 $83 $140
Total $238 $520

How does this work? Well, you get to use one filter less, and if you need a stop in between, just use the higher value and then stop down the ISO to 6400.

Assuming ISO 12800 is as good as ISO 3200

This allows you to reduce one more filter:

Optical Density Stops Stops you get by stacking Approx Price (77mm) Approx Price (4×4)
0.9 3 3 $43 $120
1.8 6 9 $89 $140
3.0 10 13,16 $83 $140
Total $215 $400

In this case, you only need three filters, and you can stop down two stops to ISO 12800 and carry on shooting.

At this point I don’t know which will be the best option. I will reserve judgement until the camera actually ships and I’ve tested it. Either way, you can see that stacking or otherwise, multiple ND filters are not a cheap proposition. Therefore, the next option might be more popular!

Variable ND filters

I recommend the following ranges at 77mm:

 
As you can see, these are not cheaper. I will never recommend cheap vari-ND filters. Variable ND filters are more convenient to carry, and you don’t need to change them around as much.

For other filers, such as polarizing, split/grad ND, IR, etc., check out my recommendations in the Complete Guide to Lens Filters.
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Sony A7s Rigged Tripod

Internal Recording

The Sony A7s comes in three versions:

  • PAL
  • NTSC
  • Both

 
Depending on which country you might purchase from, you might have only one of the above options. You might want to make sure you purchase the option with the frame rate you want. Here’s how they differ:

Res. PAL NTSC Codec Data Rate Mbps Wrapper
1080p 24p, 25p, 50p 24p, 30p, 60p XAVC S 50 MP4
50p 60p AVCHD 28 MP4
25p, 50i 24p, 60i AVCHD 24 MP4
25p, 50i 24p, 60i AVCHD 17 MP4
720p 100p 120p XAVC S 50 MP4
1440x 1080 25p 30p MPEG-4 12 MP4
640x 480 25p 30p MPEG-4 3 MP4

To record internally, I would recommend XAVC-S. All three codecs are a variant of MPEG-4 AVC/H.264 family, though XAVC is the easiest on your editing system. Within XAVC, I recommend you always record at the highest data rate, which is 50 Mbps. XAVC is supported by most of the major NLEs, including Adobe Premiere Pro, FCP-X and Sony Vegas Pro.

This is how the data rate would translate into hard drive space:

  • 375 MB/minute
  • About 23 GB/hour
  • A 16 GB card will hold about 40 minutes worth of footage in 1080p.

 
The cards supported are:

  • Memory Stick PRO Duo,
  • Memory Stick PRO-HG Duo,
  • Memory Stick XC-HG Duo,
  • SD memory card,
  • SDHC memory card (UHS-I compliant),
  • SDXC memory card (UHS-I compliant)

 
I would suggest SDHC or SDXC cards, obviously Sandisk (specifically Sandisk Extreme Pro). You don’t need any faster SD cards than already used by DSLRs. Class 10 should be absolutely fine for video.

However, the main draw of the Sony A7s is its ability to record 4K. That’s what we’ll look at in Part Five.

 

6 replies on “The Sony A7s 4K Guide (Part Four): Filters and Internal Recording”

  1. Sareesh Sudhakaran Very nice article which should put to bed the generic advice he gave during a trade show video regarding exposing S-Log2 and S-Log3 where he mentioned under exposure for S-Log2. In this new article, Alister nailed the explanation of the exposure compromises with the A7s right on the head and provided some excellent advice. I’ll be looking forward to part 2 and should be checking out his LUT sets soon.
    Thanks for sharing this!

  2. Sareesh Sudhakaran Provided that there is enough head room in the highlight area, then overexposing S-Log2 reduces a lot of the annoying blue noise that is characteristic of this sensor in shadow areas of interest. You can find a discussion about this issue on the <a href=”http://www.dvxuser.com/V6/showthread.php?324777-A7s-sample-footage&p=1986456314&viewfull=1#post1986456314″>dvxuser.com forum</a>.
    Personally, I think placing 18% gray at 32% IRE and up to 2-stops over works well — again, provided that we’re not clipping highlights. However, given the shadow noise issue, I’d stay away from Alister Chapman’s (Sony ICE) advice of underexposing S-Log by 2-stops to protect highlights, at least on this camera.

  3. First of all, love the blog. Very informative, highly technical, and overall excellent communication skill. Thanks for all the hard work you’ve put into the web site.

    I must agree with everything you’ve pointed out in this post. However, I would like to add the following with respect to exposing for the Sony A7s:

    1) When exposing for S-Log2 on the A7s (min. ISO 3,200), it’s common practice to overexpose by two stops (+2 EV), so one should take that into consideration when calculating how much filtration is needed.

    Case in point, I recently bought a 10-stop ND filter by B+W to replace a Vari-ND (soft, polarizing, and max. 7 stops of filtration) on bright sunny days. By the Sunny 16 rule (f/22, 1/50 sec, ISO100), an ND 3.0 would bring me to ISO 3,200 (5 stops) and f/4.0 (5 stops). However, in order to expose at +2 EV, I have to push the ISO to 12,800 or open the iris further, or use a combination of these.

    And if ambient light drops, I might have to push that ISO even higher. Things get worse if I’m using the long end of a slow zoom lens (f/5.6 wide open and soft or its sharper f/8.0 aperture). For these reasons, I might end up getting a 6- or 7-stop ND as well to keep the ISO as close as possible to the camera’s native ISO of 3,200.

    2) When using any of the higher contrast picture profiles (e.g., Cine-2 gamma), one can use ISO settings lower than 3,200, all the way down to ISO 100.

    In such cases, one can make do with lower levels of ND filtration. In my example above, I’d use a 6-stop ND filter to bring the exposure to f/4.0 and ISO 200. For the zoom lens, I’d push the ISO to 800 and use f/8.0. I am not sure if there’d be any significant image quality loss (certainly loss of dynamic range) for using low ISO values such as 100 or 200, but I’m hoping that won’t be the case.

    Anyway, that’s my take on the subject for anyone who, like me, cannot afford a whole set of ND filters at the moment. 

    Sorry for the long comment though and keep up the good work. Cheers from LA.

    1. That was very helpful. From what I’ve seen, I don’t want vari nd filters, prefer fixed. Just not sure which ones to begin with. Ideally, would like to have all, but can start with two or three not sure which. I think 10, 6 and maybe 3. Not sure.

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