Slow, quick, quick, slow!

[Viewmaster]

Has anyone ever experimented with a fast/slow motion NBTV here?
The bandwidth would have to be increased to run a Nipkow very fast for slow motion recording, but less when running slow for fast motion playback.
Probably quite a challenge to get the Nipkow running and syncing at all these hugely differing speeds.... Say from 4FPS up to 65FPS would be a good start. Then onto very high speed to capture a bullet in flight!

Next project anyone?
Albert.

[Andrew Davie]

Has anyone ever experimented with a fast/slow motion NBTV here?
The bandwidth would have to be increased to run a Nipkow very fast for slow motion recording, but less when running slow for fast motion playback.
Probably quite a challenge to get the Nipkow running and syncing at all these hugely differing speeds.... Say from 4FPS up to 65FPS would be a good start. Then onto very high speed to capture a bullet in flight!

Next project anyone?
Albert.

Yes! I did some experimentation at higher frame rates, as noted in my construction notes part 2 (I think). In short, I took NBTV signals and used a sound-editor to "speed up" the sound by x%. This 'fast' signal was then fed to my telvisor and I was pleased to see that my stock-standard synch circuit was quite able to synch the picture up to 2x normal speed (just!). That is, I was watching 25fps images, and it really made quite a significant improvement. The really interesting thing (to me) is that the image brightness is the same because, although the holes are only showing at half the duration (they whiz by twice as quick), they are also whizzing by twice as often. So the real visual effect of speeding up the image is just less flicker. Another side effect, though, is lots more noise from the spinning disk and motor -- it becomes something that's almost scary to be near

The video produced via this method, of course, appears to be in fast-motion, as each second of video is now being shown in half a second.

Another consideration was the vertical resolution -- as the holes are now scanning a scanline in half the time, we should start to see some degradation of resolution. Well, basically, I didn't really see anything noticeable. Perhaps at 2x speed it was slightly worse -- but perhaps not. Certainly, picture quality (ie: resolution) was excellent at well above 'normal' speed. I guess it depends on your light source's responsiveness.

[Steve Anderson]

I did some experimentation at higher frame rates, as noted in my construction notes part 2 (I think). In short, I took NBTV signals and used a sound-editor to "speed up" the sound by x%.

Another consideration was the vertical resolution -- as the holes are now scanning a scanline in half the time, we should start to see some degradation of resolution. Well, basically, I didn't really see anything noticeable. Perhaps at 2x speed it was slightly worse -- but perhaps not. Certainly, picture quality (ie: resolution) was excellent at well above 'normal' speed. I guess it depends on your light source's responsiveness.

On the assumption that the 'conventional' NBTV signal occupies a bandwidth to (say) 10kHz or so, a 'sped up' version by a factor of two should be quite happlily reproduced by a sound card or CD player. Above that you will start to notice a drop in resolution simply as a result of the limited sound-channel frequency response.

The rest of the chain including the LEDs etc. is so wideband you can almost forget it, the limiting factor is the use of a sound channel, both at high frequencies and low.

Which is why a standard analogue 625 TV signal has a baseband out to 5MHz or so, some 500 times more than a NBTV signal.

Steve A.

[Viewmaster]

deleted

[Viewmaster]

I did some experimentation at higher frame rates, as noted in my construction notes part 2 (I think). In short, I took NBTV signals and used a sound-editor to "speed up" the sound by x%.

On the assumption that the 'conventional' NBTV signal occupies a bandwidth to (say) 10kHz or so, a 'sped up' version by a factor of two should be quite happlily reproduced by a sound card or CD player. Above that you will start to notice a drop in resolution simply as a result of the limited sound-channel frequency response.
Steve A.

But for true slow motion NBTV recording we need a NBTV camera that can run at, say, 64 FPS and record this to a PC. The PC can easily handle this bandwidth as miniDV if converted on the hoof. MiniDV is already recorded into and out of a PC at about 3meg with .avi files.

So a NBTV/miniDV/NBTV converter would do it. Now that's a nice piece of software kit....I wonder if Dixons sell it?

As the NBTV camera will run fast at 64FPS and and slow at 4 FPS it could be called a Niiiiiipppkw. Like the old 8/16mm film Bolex cameras did.

It would be the camera with all the problems, as the NBTV viewer would always run at std 12.5 FPS in order to get the true slow/fast motion effects from the recordings.
Albert.