On to 80 lines

Forum for discussion of narrow-bandwidth mechanical television

Moderators: Dave Moll, Andrew Davie, Steve Anderson

On to 80 lines

Postby Panrock » Wed Oct 10, 2007 11:44 pm

My plans for the next convention. And they still are just plans... :lol:

Details HERE
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: On to 80 lines

Postby Steve Anderson » Sat Dec 29, 2007 6:06 am

Panrock wrote:My plans for the next convention. And they still are just plans... :lol:

Details HERE


I had a wander around this site over the past hour or so, and it represents one of the few facets of living in the UK that I miss...

THE BRITISH HERITAGE TELEVISION PROJECT...

http://www.copycoder.com/phpbb2/index.php

Not only did I look at the NBTV pages, but also those (the majority) concerned with British 405-line TV. It's great to see a band of guys get together and, with all due respect, continue the legacy of a technologically defuct system. The same could be said of NBTV. Well done to all those involved.

..the other thing I miss about the UK is the pubs......er, I can't think of much else.

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 5360
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Postby Panrock » Thu Jan 17, 2008 8:00 am

Tonight the stainless steel discs are being sprayed up. I'll be trying each in the monitor in turn to check raster quality and poke out any of the little holes that need it etc.
Attachments
discs.jpg
discs.jpg (61.56 KiB) Viewed 17071 times
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Panrock » Fri Jan 18, 2008 8:49 am

Unfortunately the discs are not satisfactory. The mean hole diameter is 0.6mm round, not 0.28mm square. This means the definition will barely reach 40 lines. It looks like I've reached the limits of everyday laser cutting. :(

If anyone can help with procuring better discs, please let me know. Otherwise I shall probably revert to 30-lines and concentrate on improving the stereo.

Another option might be to go for 60 lines instead, when holes of such size would be about right...

Steve
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Stephen » Fri Jan 18, 2008 9:34 am

Panrock wrote:Unfortunately the discs are not satisfactory. The mean hole diameter is 0.6mm round, not 0.28mm square.
It seems to me that you could draw transparent 0.28 mm windows around a spiral of correct diameter within a black background circle in a PC drawing application and print the resulting drawing on a transparency to form a "mask" for each disc. You could glue the transparency to one side of the disc. Each 0.28 mm square window would fit over a corresponding one of the 0.6 mm round apertures to form a square transparent disc aperture of correct size.

The degree of opacity for the black portion of the transparency would not be a detrimental factor in this instance because most of the light would be blocked by the disc. The major issue would be procuring a printer and transparency sheets large enough to produce masks large enough for the discs.
Stephen
User avatar
Stephen
Anyone have a spare straightjacket?
 
Posts: 427
Joined: Fri Jan 26, 2007 7:00 am

Postby Panrock » Fri Jan 18, 2008 9:10 pm

Yes Stephen, this had occurred to me and I could certainly do this. However the problem will be the light loss through the 'transparent' portion of the acetate. I have experience of this, since once I had discs 'with windows' printed from a CAD file.

Moreover, even with 0.6mm holes and 12 luxeons illuminating it, I've noticed the brightness of the display is now only just sufficient. With 0.28mm holes it would be a quarter of this. Any further losses due to the acetate would be a serious matter.
I'm now reconsidering; and am beginning to think a 50-line display with square holes would be more practical for this size of disc.

Steve
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Viewmaster » Fri Jan 18, 2008 10:51 pm

Just a suggestion.......use kitchen aluminium foil used for baking in place of a transparency. This will give you 100% light transparency.

If you made a punch in steel made from a hard steel darning needle and stoned to shape to the .28mm sq you require....very short shankonly is required for strength, (about 1/32")

The die is then the problem. Experiment with hard rubber/wood as the bottom uncut die. A cut die is preferable but difficult to make sq!
Use a small pillar drill as the press (Punch in the chuck) and lower the chuck down into the foil.....or a model lathe if you have one.

(I have punched out plastic sheet etc in this way, but as it was a round hole the die was easy to make.)
Albert.
User avatar
Viewmaster
Frankenstein was my uncle.
 
Posts: 1306
Joined: Fri Apr 06, 2007 4:50 am
Location: UK Midlands

Postby Stephen » Fri Jan 18, 2008 11:00 pm

Panrock wrote:Moreover, even with 0.6mm holes and 12 luxeons illuminating it, I've noticed the brightness of the display is now only just sufficient. With 0.28mm holes it would be a quarter of this. Any further losses due to the acetate would be a serious matter.
I'm now reconsidering; and am beginning to think a 50-line display with square holes would be more practical for this size of disc.
You might want to try transparent optical discs before you give up. Transparent discs would theoretically improve the light transfer 80 times because all the light transfers through a single line, that is, the edge of the disc, rather than the area of the image. You could embed translucent pits of desired depth and spiral pattern into one side of each disc with a laser or drill.

Of course, with this sort of disc the light source concentrates its output in a single line rather than over the whole area of the image. Likewise, the PMT pickups would sense light along the edge of the disc rather than through it.

I see one source of laser-cut acrylic circles up to 24 inches in diameter at http://www.tapplastics.com/shop/product.php?pid=140& . I am sure that there are other sources that can provide the same sort of products locally.
Stephen
User avatar
Stephen
Anyone have a spare straightjacket?
 
Posts: 427
Joined: Fri Jan 26, 2007 7:00 am

Postby Viewmaster » Fri Jan 18, 2008 11:12 pm

Another thought instead of punch...use two small pieces of ali kitchen foil cut as piccy...them put them together to form a perfect sq hole any size you like. and glue to disc.
Attachments
Tin foil sq aperture.JPG
2 pieces of tin foil to form small sq
Tin foil sq aperture.JPG (4.99 KiB) Viewed 17021 times
User avatar
Viewmaster
Frankenstein was my uncle.
 
Posts: 1306
Joined: Fri Apr 06, 2007 4:50 am
Location: UK Midlands

Postby Panrock » Fri Jan 18, 2008 11:13 pm

Albert,
Yes... perhaps I could fairly simply cover all the existing holes with foil - then, working from the other side of the disc and using a powerful magnifier (I have a low power telescope eyepiece), it would be possible to punch the new little holes fairly centrally within the bigger holes. As a bonus, it would actually be easier to grind my little punch to a square than to a round!

I am still worried about the image brightness and camera sensitivity at 80 lines though.

Stephen,
Thanks for your interesting suggestion but I fear this would entail radical re-design and a completely different layout of the entire monitor and camera, with attendant difficulties of concentrating the light efficiently into a line (and also creating efficient diffusing spots) which together, I suggest, would largely negate the 80-fold theoretical increase in throughput.

Steve

PS. Albert our posts have crossed - I've just seen your next suggestion. I think this would not work so well in practice because at the very tiny scale involved, it would be difficult to produce a really clean and perpendicular corner - and 160 times over too! :)

You could use four pieces to overcome this, but you'd still also have the problem of ensuring the tiny resulting squares were exactly the right dimensions. I think your first 'punch' idea is better.

S
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Viewmaster » Sat Jan 19, 2008 5:06 am

Panrock wrote:PS. Albert our posts have crossed - I've just seen your next suggestion. I think this would not work so well in practice because at the very tiny scale involved, it would be difficult to produce a really clean and perpendicular corner - and 160 times over too! :)
S


All the corners can be overcut each way to get true 90 deg easy made sharp corners. Any light bled on the overcuts can be filled in after....not polyfilla! :)

It's all very easy to suggest all this but I agree that the practical problems are difficult and success not guaranteed anyway.


Albert
User avatar
Viewmaster
Frankenstein was my uncle.
 
Posts: 1306
Joined: Fri Apr 06, 2007 4:50 am
Location: UK Midlands

Postby Viewmaster » Sat Jan 19, 2008 5:33 am

More food for thought...2 long parallel ali strips .28mm apart. Glue on cross pieces leaving .28mm gaps.
Cross pieces can be very wide as long as gap is .28mm Forms a perfect sq. Then cut out sq holes.
Albert.
Attachments
sq holes.JPG
Sq holes foremed from strips.
sq holes.JPG (6.99 KiB) Viewed 16998 times
User avatar
Viewmaster
Frankenstein was my uncle.
 
Posts: 1306
Joined: Fri Apr 06, 2007 4:50 am
Location: UK Midlands

Postby Panrock » Sat Jan 19, 2008 6:09 am

Hmm... good ideas but 280 microns is very small when trying to measure and set gaps accurately.

I tried stoning down a pin but found it became too fragile when it got down to this dimension.

But I think I've now come up with another idea now which would be practical, though the holes will be round.

I've found some fine copper wire on a spool in the workshop. On the micrometer it measures 0.27mm in diameter. I have some self-adhesive 80-micron aluminium foil tape. I stuck a small square of this over the hole. From the other side it was easy (under a magnifier) to see the reflective aluminium through the hole and judge the centre. I found the fine copper wire would plunge through the foil without bending.

The resulting hole was about the right size but not perfectly round. So next, I shall try backing up the foil with a plasticene temporary backing. More anon...

Steve
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Panrock » Sat Jan 19, 2008 6:54 am

That helped a bit, but I really need something that doesn't tear when it's punched, as does foil. The resulting holes would be usable but not ideal.

I need something easy to push through, which will keep its shape, and which won't push out of the hole like plasticene does... I'm now trying shoe polish wax.
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Viewmaster » Sat Jan 19, 2008 7:17 pm

Panrock wrote:... I'm now trying shoe polish wax.


Ah, now at the next convention at Loughboro' I shall look for the guy with the shiny shoes! :lol:
Albert.
User avatar
Viewmaster
Frankenstein was my uncle.
 
Posts: 1306
Joined: Fri Apr 06, 2007 4:50 am
Location: UK Midlands

Next

Return to Mechanical NBTV

Who is online

Users browsing this forum: No registered users and 26 guests

cron