gary wrote:Sorry Harry I think I have made a couple of incorrect assumptions, let me tell you what I think is happening and you can tell me if and where I am wrong.
I assume NBTVA standard 32 line
Hi Gary sorry i had to go out again so couldn't reply ,so at the moment looks like not unless i swap the swinging mirror with rotating mirrors .
I would not think to correct you on NBTV you know much more than i ever will ,i can try and explain best i can what i see if i do a working experiment .
My little achievements on this are a step forward i know its taking a while so hope i am not boring any one .
The polygon mirror is your line scan, and as it has 6 facets it would need to rotate at 400/6 revs per second (4000 rpm).
Yes i am working the little ex dvd motor thats what the polygons rotating at but my pulley system ratio the motor must be greater than that .
The vibrating or oscillating mirror is the frame scan @ 12.5Hz - but here we start to get into difficulties because an oscillating mirror doesn't have instantaneous flyback it scans one way and then back the other, presumabley at the same speed and thus you have an effective frame rate of 25Hz with each alternate frame having the frame scan direction reversed (actually it's worse than that because of the sinusoidal nature of the oscillation the speed of line scan varies along it's length). That accounts for your double image then I suppose. It also seems to me that you would want to halve your speed rather than double it. You would still have the frame direction changing every other frame but if you displayed the signal the same way it would be corrected!
I doubled checked Gary i could only find one of the projects so far using a resonance but Yep i was wrong it was half the frame frequency as you say ! ,perhaps then speculating instead of an image either side it will meet in the middle double the size just thinking whats happening .
Half the speed would i suppose tend to be easier for moving the mirror,but If using oscillating mirror may mean its not true NBTV standard ,if it can't do a 12.5 hz but half that oh well thats still interesting .
Does it mean the line has to be 800hz then a frame rate at 12.5 would work ...any case as is this is enough of a problem for me for now .
So unless you have worked out a way to have the mirror trace a saw tooth rather than a sinusoidal path, It would seem you can still get a picture out of it but that it will be decidedly non-standard - but why should that stop you? LOL I might be coerced into adding your new standard to TBP...
No no just a sine wave so at 6 hz fine for a still image but moving a little jerky
BTW This is why Alan Short (and others) use either a cam operated mirror (or arm) or another mirror polygon - the cam gives near instantaneous flyback and the mirror polygon doesn't have any flyback at all.
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Yes i understand that cam makes a mechanical sawtooth ,he did try the speaker idea for the frame mirror for a simple camera i read but he must of had the same problem as here ..
The 2 625 line versions i saw use frame mirror resonance ...so at half frame rate they must also not be true standards either .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.