How to film your televisor

A "new fashioned" televisor, using an Arduino to drive the motor and display.

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How to film your televisor

Postby Andrew Davie » Thu May 18, 2017 11:13 pm

While I'm struggling with the custom framing, I had a bit of a play with how to best get video/footage of a televisor in action.

Images from mechanical televisors are notoriously difficult to film. This is in part due to their flickery nature and the low frame rate (12.5fps). Modern video cameras (or smartphones) have much higher frame rates, and the difference between the camera frame rate (or more specifically the exposure time) and the televisor frame rate means that usually vertical bands of black are seen rolling along the resultant video. That's when the televisor is filmed in "good light".

This video is a bit of a demo of that effect, and the opposite effect. Bands of black shift to the right on a "standard" televisor being recorded in good lighting conditions, and bands of white shift to the left on the same televisor being recorded in dark conditions. This is due to (in my case) the camera aperture (or exposure time if you like) adjusting automatically based on the measured light. So, there's a crossover point - when there's not enough light for the black banding to form, but too much light for the white banding to occur.

So in this experiment I pointed a standard desk lamp over my shoulder towards the televisor display. I then played with obscuring that light by partially shading it with my hand. I was easily able to control the transition from black banding to white banding - and none at all, just by how much light I allowed. A dimmable light would be a great tool for recording mechanical TV video output.

There is a small artefact visible in a set position on the frame when the light is "just right", and you can catch this position pretty much anywhere based on your timing.

Of course, to the human eye, mechanical television doesn't look anything like the images you see here. The human eye sees a much more flickery, but constantly flickery picture.


youtu.be/T9ScyMrOJhw
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Re: How to film your televisor

Postby Klaas Robers » Fri May 19, 2017 5:38 am

Andrew, do I see corrrectly that when there is a scene change, where the mean scene brightness changes too, that the black band or the white band appears again and you have to change the compensating back ground ilumination?
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Re: How to film your televisor

Postby Andrew Davie » Fri May 19, 2017 11:33 am

Klaas Robers wrote:Andrew, do I see corrrectly that when there is a scene change, where the mean scene brightness changes too, that the black band or the white band appears again and you have to change the compensating back ground ilumination?


You do - yes. That's because the picture itself is contributing sufficiently to the area being measured for brightness. There's a pretty narrow range band between "white stripes" and "dark stripes" and if you're on the edge of that range then the picture itself is sufficient to trigger the banding. However,if you're in the middle of that range, then the picture won't make much of a difference. This is all with my phone, of course - your mileage may vary.

In short, yes the picture can change the effect, but it's possible to adjust the lighting so the picture doesn't change the effect.
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Re: How to film your televisor

Postby smeezekitty » Mon Apr 16, 2018 3:24 pm

Did you ever have any problems focusing? What kind of camera are you using?

Everything I try refuses to focus on the it
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Re: How to film your televisor

Postby Andrew Davie » Mon Apr 16, 2018 5:13 pm

Sometimes focus was an issue, but i generally was able to focus on something nearby and then the screen. I used a cheap android phone.
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