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Re: Double wheel nipkow disc

PostPosted: Tue Sep 04, 2018 2:49 pm
by Steve Anderson
Hello Rob, and welcome to the forum.

Certainly an interesting prospect, but correct me if I'm wrong, wouldn't the resultant image be even more 'curved' than the usual Baird arrangement?

Today that could be compensated for by some electronics to remove the distortion - but I guess it depends on how the camera scans the subject. If it's in the same manner then all (I would think) should be OK. But it does potentially lead to compatibility problems.

I'm not being 'negative' on the idea at all - but it possibly is an issue that needs addressing...otherwise I'm very interested in further developments.

Steve A.

Re: Double wheel nipkow disc

PostPosted: Tue Sep 04, 2018 8:22 pm
by Harry Dalek
HI welcome also to the forum .
Looking at your idea if i got it right your stuck at a low line rate but increase screen size yes ....it is different but doing a 2 disk or 2 drum system if you went with a 2 slit disk or drum you would have some thing that is multi system ,you could do any thing up to 60 line and you still have increase screen size ... look at this page and the links on the page ...Maksim stuck with one line rate system 32 line but it is really could do multi systems if you increase your line speed ..i did it with pulley system on the line drum to get 32 48 and 60 line ..got crappy results due to vibration higher i went due to the thin drum plastic but it does work ...it would be a lot easier on a 2 disk system ...any case i like your animation and i understand it is what is is a new idea and well worth making if you are keen on making that one ..
viewtopic.php?f=1&t=2557&start=30

Re: Double wheel nipkow disc

PostPosted: Wed Sep 05, 2018 2:10 pm
by Robonz
I have not thought too hard about this, but I think you can achieve the same thing using a 4 turns spiral Nipkow disc and putting another disc behind it at 1/4 the speed that selects which spiral is active. This method would let you use a standard NBTV video signal. I was thinking about trying this myself.

Cheers
Keith

Re: Double wheel nipkow disc

PostPosted: Mon Sep 10, 2018 6:21 am
by Klaas Robers
Interleaving looks to be a clever system, but it isn't. It assumes that you stay looking at a fixed point in the image. That is not happening. Your eye is hovering over the picture. In this interleaving case you will experience a very course picture of 8 lines, which are moving over the picture. This will spoil the resolution as your eyes/brain cannot recombine the contents of the moving lines. Only if you make a photograph with an exposure time of 1/12.5 second, or longer, you will see the true resolution of the picture.

Re: Double wheel nipkow disc

PostPosted: Mon Sep 10, 2018 12:13 pm
by Steve Anderson
Klaas is correct. Some years ago I tried an interlaced arrangement, simply a white raster on a scope screen, 16 lines interlaced 2:1, and 8 lines interlaced 4:1. A dismal failure, the flicker was far worse than no interlacing at all. Line and frame rate the usual NBTVA standard.

Steve A.

Re: Double wheel nipkow disc

PostPosted: Tue Sep 11, 2018 7:33 am
by Klaas Robers
On the other hand: our eyes have a virtual exposure time of about 0.1 sec. I did in the far past (~1975) the following experiment at our Philps Research Lab:
- A standard 625 line black and white TV-monitor,
- displaying the standard RETMA black and white test chart,
- Superimposed on the video signal I put white noise,
- this gives a moving grainy "snow" over the test chart.
- just as if you receive an analogue TV station from what greater distance.

- Then I made (polaroid) photos from the monitor screen,
- with stepwise changing exposure times.
- With an exposure time of 1 sec. the "snow" was gone.
- With an exposure time of 1/25 sec. the snow on the photo was more heavy than subjectively on the monitor screen.
- With an exposure time of 1/10 sec the snow on the photo was comparable to what I saw on the screen.

So for noise we have eyes with a virtual exposure time of 1/10 sec.
I forgot this experiment for more than 40 years ..... and then it pops up again, as if you did it yesterday.
Memory is a strange phenomen.

Re: Double wheel nipkow disc

PostPosted: Tue Sep 11, 2018 11:52 am
by gary
Klaas Robers wrote:Memory is a strange phenomen.


I had a memory once Klaas, but I have forgotten where I put it...

Re: Double wheel nipkow disc

PostPosted: Tue Sep 11, 2018 1:52 pm
by Steve Anderson
Klaas Robers wrote:Memory is a strange phenomen.

My memory is what I forget with...

Steve A.

Re: Double wheel nipkow disc

PostPosted: Tue Sep 18, 2018 2:39 am
by rbairos
Hello,
I seemed to have received some notification of spam in my inbox, and my account was removed.
Apologies for posting here, but it seems posts to topics I started (including this one), have been removed as well, so I missed all these replies ?
Confused,
Rob.

Re: Double wheel nipkow disc

PostPosted: Tue Sep 18, 2018 1:45 pm
by Andrew Davie
rbairos wrote:Hello,
I seemed to have received some notification of spam in my inbox, and my account was removed.
Apologies for posting here, but it seems posts to topics I started (including this one), have been removed as well, so I missed all these replies ?
Confused,
Rob.



I do apologise. We have been attacked, and I have been doing my best to remove all the bogus accounts.
In your case I appear to have made an error - very sorry about that.

Re: Double wheel nipkow disc

PostPosted: Tue Sep 18, 2018 11:03 pm
by rbairos
That's okay.
Is there any chance the original post of this thread can be restored?
It had an animated gif that described the concept being discussed here.
Cheers,
Rob.

Re: Double wheel nipkow disc

PostPosted: Wed Sep 19, 2018 12:31 am
by Andrew Davie
rbairos wrote:That's okay.
Is there any chance the original post of this thread can be restored?
It had an animated gif that described the concept being discussed here.
Cheers,
Rob.


There is nothing I am aware of that I can do to restore the posts.

I checked the moderator logs and I can't find where I actually deleted you or your posts; though I have no doubt that the culprit was I.
I've had to deal with many tens of bogus accounts and once again I apologise that you got caught up in my response.
I hope that you can re-post. I know it's inconvenient.

Re: Double wheel nipkow disc

PostPosted: Wed Sep 19, 2018 2:02 am
by rbairos
No problem at all.
Here's the gif for reference:

Re: Double wheel nipkow disc

PostPosted: Wed Sep 19, 2018 2:03 am
by rbairos
No problem at all.
I found the gif, but get this error when submitting the post:

General Error
You are not allowed to access this file.
Please notify the board administrator or webmaster: andrew@taswegian.com

Re: Double wheel nipkow disc

PostPosted: Wed Sep 19, 2018 2:04 am
by rbairos
Trying again..
output.gif
output.gif (6.56 MiB) Viewed 4375 times