[Ronja] Further lcd thoughs...

[ronjalist]

Cluestick gratefully received :-)

What if the optics on the rx were focused to fill the ccd of a webcam 
(which has had it's ir filter removed),  Or is it that optics for a 100 
meter zoom shot are too bulky, need or too high a precision or are 
simply too costly ?

If the optical zoom is high enough surely the output power only need to 
be above ambient to illuminate ?

I just thought that as we are now looking for an image - not a light 
level we could get funky with the rx lenses ?


J.D. Bakker wrote:
> At 02:11 +0100 07-09-2008, ronjalist wrote:
>> OK 50Hz is not enough, but you do have 1024x768 (or better) resolution
>> and you could forgo the main optics, use a fresnel lens and subdivide
>> the panel into 1000 segments...
>>
>> With a telescopic lens arrangement and an lcd webcam as the rx.
>>
>> Thoughts ?
> 
> It'll work, but at the expense of link range. Assuming equal transmit 
> power, and comparing two systems with comparable optics (no fair 
> giving a telescope to the webcam and not to the regular Ronja), each 
> of those 1000 segments will have 1/1000th of the total power. 
> Achievable link distance is roughly proportional to the square root 
> of power, so those 1000 segments reduce the max link distance by a 
> factor of ~30, to just over 40 meter for a standard Ronja config.
> 
> Now, in the real world,
> 
> - LCD panels transmit less than 50% of all incident light
> - on top of that, a significant portion of the light (>60%) will be 
> diffused/diffracted off-axis. This leaves only 10-20% of all 
> transmitted energy to hit the receiver
> - you *will* need some separation between segments, or accept that 
> light from one segment will bleed into the next one. This, too, costs 
> TX energy.
> - alignment is going to be harder
> + on longer ranges, in-air absorption will eat more energy than the 
> square law suggests (so this would work in favor of a short-range 
> segmented system)
> 
> More on link budgets here:
> 
> http://www.pointless.net/pipermail/ronja/2006-August/009130.html
> 
> JD 'no free lunch' B.