NEX-FS700 Significantly reduced shutter when in Super Slow Mo!

UPDATED WITH NEW FRAME GRABS FROM STROBE LIGHT AT BOTTOM.

One of the things that did concern me slightly about the FS700 was how would the sensor behave in Super slow Mo. The sensor is a CMOS sensor, so I expected it to exhibit rolling shutter artefacts, which it it does indeed do when in standard shooting modes and S&Q motion. It’s not bad, but you can make the pictures skew and when you try to shooting something like a spinning propellor you can get some weird effects, especially at higher shutter speeds. However when you switch the camera to Super Slow Mo the rolling shutter effects appear to go away. I was able to shoot propellors, do fast pans, shake the camera about etc and there was little sign of the usual rolling shutter artefacts.

FS700 25P 1/100

Just take a look at these two frame grabs. One shot done at 25P with a 1/100th shutter, the other done at 100fps with a 1/100th shutter, so in both cases the shutter speed is the same, so you would expect the rolling shutter artefacts to be the same, but clearly they are not. In standard mode the fan exhibits a typically lop sided, asymmetrical look and the fan blades appear curved, the upper and lower fan blade both bent towards the right of the frame. But in Super Slow Mo mode the fan blades are straighter and the fan is a lot more symmetrical with noticeably less bias towards the right, notice in particular the differences in the lower fan blade.

FS700 Super Slow Mo 1/100th shutter

You can tell the shutter periods are the same as the amount of motion blur and spreading of the fan blades is near identical, so it’s not a shutter speed difference, this is clearly a sensor scan difference. This is very interesting and requires further investigation as it suggests that the sensor read out process is different in the high speed mode. It is probably just a significantly faster scan rate, but it could also possibly be a global shutter of some kind. It’s just a shame that you can’t access this read out mode for normal shooting.

UPDATE:

FS700 Flash band at 25fps 1/100th shutter.

FS700 Flash band at 25fps 1/100th shutter.

Here are a couple more frame grabs done with the strobe focussing flash from a Canon DSLR. In both cases the shutter speed is 1/100th of a second so you would expect the width of the “Flash Band” to be the same. The narrower the band, the slower the sensors scan speed. These frame grabs suggest the scan speed is around twice as fast when in Super Slow Mo. It’s not a global shutter, but certainly a nice improvement. This is 100% repeatable.

FS700 Flash band in Super SlowMo 100fps, 1/100th shutter

You can take advantage of this for normal speed shooting by setting the camera to SSM and  recording the SDior HDMI feed to an external recorder.

Speculation: There is a little more aliasing when shooting in SSM. Is there some line slipping going on perhaps during SSM? This would allow a faster scan speed as fewer lines of pixels are read and thus might account for both the slight aliasing increase and the faster read out speed.

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Monday, July 9th, 2012 Uncategorized

6 Comments to NEX-FS700 Significantly reduced shutter when in Super Slow Mo!

  • Matt says:
    July 15, 2012 at 2:01 am

    Alister,
    I wanted to repeat a question that someone asked you in April: used F3 or new FS700? At the time it sounded like you were only starting to use the FS700. Since then, I have seen you make a lot of positive comments about the FS700. Is it now a slam dunk for the FS700 or the other way around. I am an aspiring (amateur) film maker but have the budget to splurge on a camera in that range. Your opinion would be appreciated.
    Thanks,
    Matt

    Reply
    • alisterchapman says:
      July 15, 2012 at 8:53 am

      A lot depends on what you want and how much you are prepared to spend. To get the best from the F3 you will want an external recorder, some way to power the recorder and a mounting system. This adds to the cost. The F3 does produce a better image than the FS700, especially if you use S-Log, but it’s not a night and day difference and a well handled FS700 produces an image that is 95% of the F3′s pictures. As I’m sure you know the FS700 has slow motion and built in 50/60p but has no cache record. I think the F3 ergonomics are better than the FS700′s, but when you use an E-Mount lens on the FS700 you get autofocus, auto iris and image stabilisation.

      There is no clear winner and no clear “better” all round camera. If your primary concern is getting the absolute best image quality then the F3 would be the one to go for, but if you don’t need that very small edge that the F3 has then the money savings and extra features of the FS700 may make that the better choice provided you are happy with the strange ergonomics. My advice would be to hire them both for a couple of days and try them for yourself. They are both very capable cameras, but behave and handle quite differently.

      Reply
  • Sinclair Stammers says:
    July 18, 2012 at 7:46 pm

    Alister, I have been practising with SSM on the FS700, my subject was jumping grasshoppers, at 200fps the motion was too fast so I tried 400fps which showed the movement more successfully. At both frame rates if I go through footage frame by frame the grasshoppers are quite blurred even though I had set the shutter speed to 1000th second. My question is when using SSM does changing the shutter speed have any effect or is the shutter speed chosen by the camera automatically? I can’t find any reference to this in the manual, so your feedback would be much appreciated.

    Reply

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