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90 deg Shutter angle?


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#1 Dominik Bauch

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Posted 23 March 2017 - 04:50 PM

I have a shoot coming up that will involve a lot of filming laptop screens.

I'll be using a slider as well as long lenses to follow action close up on the screens.

 

The slider moves will be relatively slow, even so at 180 shutter the motion blur obscures more than I would like

I was testing 90 degree shutter, I definitely can afford to lose a stop so that's not a concern. To my eye, given the slow moves, it looked better. The screen content was clearer and strobing wasn't obvious.

 

Is there any obvious reason why this is a bad idea? I can't think of any, aside from potential strobing or flicker with practical lights.

 

Also planning on using Summicon C's for the shoot. I've done a bunch of testing with Cp.2 super speeds and I'm not getting any laptop screen moire apart form with the 135mm lens.

Are the Summmicrons very sharp? Anyone noticed moire-ing with those?

 

Thanks in advance for any thoughts.


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#2 Satsuki Murashige

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Posted 23 March 2017 - 06:23 PM

If the screens are live and not being composited in later, then it would be bad if the screens pulsed or flickered due to the shutter speed of the camera. The dimmer you make the screens, the more they pulse (or at least, the more visible the pulse becomes).

So it would be best to shoot tests of all of the actual screens you will be using to make sure that doesn't happen with your 90 degree shutter angle. I don't know what frame rate you are shooting at, but obviously that will be a factor in determining your shutter speed as well.

I think if pulse or flicker is a concern (as it usually is with live screens), it may be smarter to switch the camera to shutter speed mode instead of shutter angle (assuming that you are using a digital camera). That way, you can be assured of getting the exact shutter speed required. This will be less of a concern if you are in PAL land and shooting 25.000fps rather than 23.976 or 29.97. Either way, be prepared to spend some time in prep or on set fiddling with the shutter in syncro scan mode.
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#3 Dom Jaeger

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Posted 23 March 2017 - 08:37 PM

Regarding the lens selection, moire is caused by the frequency of image details resonating with the size of the sensor photosites, so unless you're using very low resolution lenses that can mimic the effect of a low pass filter by blurring or reducing the contrast of that detail, I don't think the choice of lens brand should matter. Most modern lenses can resolve much finer detail than the size of a 4K sensor photosite, certainly Summiluxes and CP.2s. A longer focal length will magnify the detail, and at a particular magnification (or distance) you might get moire, but it's really a function of the sensor (and whatever OLPF the camera has), not the lens.


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#4 Satsuki Murashige

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Posted 23 March 2017 - 09:26 PM

A longer focal length will magnify the detail, and at a particular magnification (or distance) you might get moire, but it's really a function of the sensor (and whatever OLPF the camera has), not the lens.


Yup. If you change the magnification of the LCD screen by either physically moving closer with the camera or using a different focal length, the moire should go away.
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