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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

projecting an image



 
 
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  #21  
Old April 3rd 15, 10:02 PM posted to uk.d-i-y,uk.tech.digital-tv
Bill Wright[_2_]
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Default projecting an image

alan_m wrote:
On 03/04/2015 20:30, Bill Wright wrote:

But surely I need a much longer focal length? A normal 35mm camera lens
will cover an area about 1" by 1.5" at a distance of about 50mm.


And if you reverse the lens?


The image is very small and is 50mm from the lens.

I've experimented with a large magnifying glass and that appears to have
a focal length that's more suitable. It's about 600mm.

Bill

Bill
  #22  
Old April 3rd 15, 10:04 PM posted to uk.d-i-y,uk.tech.digital-tv
Capitol
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Posts: 13
Default projecting an image

Bill Wright wrote:
Andrew Mawson wrote:

Google 'camera obscura'


The problem is finding a lens of suitable focal length. This isn't the
method I'm half remembering anyway.

Bill


It doesn't use a lens, it's a pinhole camera.
  #23  
Old April 3rd 15, 10:11 PM posted to uk.d-i-y,uk.tech.digital-tv
[email protected]
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Posts: 45
Default projecting an image

On 03/04/2015 20:13, michael adams wrote:
"Norman Wells" wrote in message
...
"Bill Wright" wrote in message
...
I need to project or otherwise place an image on a wooden board so I can paint it on
the board by using it as a guide. I don't have an overhead projector. I have some
transparent media for a laser printer and I have a 60 year old 6cm projector in the
loft but I don't want to dig it out and the bulb will blow and the whole thing will be
annoying.

Isn't there some way the old painter guys used to do this, just with a mirror or
something?

Come on gentlemen and ladies, ideas?


You need a lens from an old 35mm single lens reflex camera. Mount it, eg in a hole
through another board, so you can securely position it where necessary between the
well-illuminated original and the target board so as to form an image on it of the
right size.

You may need to darken the room, especially if the image you want is large.


The resulting image would be upside down and reversed left-right.

That's where all the mirrors, prisms and all the rest of the
tricky stuff comes in.




Like rotating it 180 degrees?
  #24  
Old April 3rd 15, 10:15 PM posted to uk.d-i-y,uk.tech.digital-tv
[email protected]
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Posts: 45
Default projecting an image

On 03/04/2015 20:31, Bill Wright wrote:
michael adams wrote:
"Norman Wells" wrote in message
...
"Bill Wright" wrote in message
...
I need to project or otherwise place an image on a wooden board so I
can paint it on the board by using it as a guide. I don't have an
overhead projector. I have some transparent media for a laser
printer and I have a 60 year old 6cm projector in the loft but I
don't want to dig it out and the bulb will blow and the whole thing
will be annoying.

Isn't there some way the old painter guys used to do this, just with
a mirror or something?

Come on gentlemen and ladies, ideas?
You need a lens from an old 35mm single lens reflex camera. Mount
it, eg in a hole through another board, so you can securely position
it where necessary between the well-illuminated original and the
target board so as to form an image on it of the right size.

You may need to darken the room, especially if the image you want is
large.


The resulting image would be upside down and reversed left-right.

That's where all the mirrors, prisms and all the rest of the
tricky stuff comes in.


I suppose at a stretch I could print the original really small and mount
it at the focal point, and illuminate with something very very bright.

Bill


Have you got a light box or a SAd lamp?
Or a scanner that does transparencies.
They should work with a suitable lens (3 dioptre reading glasses?) and a
cardboard box to cut out the stray light.
  #25  
Old April 3rd 15, 10:50 PM posted to uk.d-i-y,uk.tech.digital-tv
[email protected]
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Posts: 45
Default projecting an image

On 03/04/2015 21:59, alan_m wrote:
On 03/04/2015 20:30, Bill Wright wrote:

But surely I need a much longer focal length? A normal 35mm camera lens
will cover an area about 1" by 1.5" at a distance of about 50mm.


And if you reverse the lens?



It makes no difference.
A 50mm focal length lens will make a 1:1 image at 100mm either way around.
  #26  
Old April 3rd 15, 11:21 PM posted to uk.d-i-y,uk.tech.digital-tv
Brian Gaff[_2_]
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Posts: 1,003
Default projecting an image

The problem with those is that they need a parabolic surface to project on
at least the ill fated one in Eastbourne did.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Andrew Mawson" wrote in message
...
"Bill Wright" wrote in message ...

I need to project or otherwise place an image on a wooden board so I can
paint it on the board by using it as a guide. I don't have an overhead
projector. I have some transparent media for a laser printer and I have a
60 year old 6cm projector in the loft but I don't want to dig it out and
the bulb will blow and the whole thing will be annoying.

Isn't there some way the old painter guys used to do this, just with a
mirror or something?

Come on gentlemen and ladies, ideas?

Bill

Google 'camera obscura'

http://en.wikipedia.org/wiki/Camera_obscura

Andrew



  #27  
Old April 3rd 15, 11:24 PM posted to uk.d-i-y,uk.tech.digital-tv
Brian Gaff[_2_]
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Posts: 1,003
Default projecting an image

Sounds like you need a sign writer then.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Bill Wright" wrote in message
...
michael adams wrote:

If possible scan the image

Load it into a DTP or Paint program

Blow it up to the require final size. Or even bigger

Trace around any lines you need as a guide, with a thick black line.

Flood fill the rest with white so as not to waste ink.

If the program has a "poster" printing option, use that.

Otherwise break it into panes manually and print it onto bank
paper. The problem with the transparent medium may be that that is
too thick to press the impression.

Print all the panels out and join them together. Turn it over and trace
over the lines with an B6 or chinagraph pencil. Offer that up to
the board and go over the lines again presing hard same as with old
fashioned tracing.


That's more or less how I did the house number for my massive illuminated
house number sign. It would be possible for this, but a lot of hassle. But
maybe . . .

Bill



  #28  
Old April 4th 15, 04:37 AM posted to uk.d-i-y,uk.tech.digital-tv
Bill Wright[_2_]
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Posts: 9,381
Default projecting an image

Capitol wrote:
Bill Wright wrote:
Andrew Mawson wrote:

Google 'camera obscura'


The problem is finding a lens of suitable focal length. This isn't the
method I'm half remembering anyway.

Bill


It doesn't use a lens, it's a pinhole camera.


There's no way it would be bright enough, unless I did it by sunlight
and rigged up a darkroom. Too much hassle. A large lens would mean I
could do it indoors.

The camera obscura as used by artists used lenses once they were available.

Bill
  #29  
Old April 4th 15, 04:52 AM posted to uk.d-i-y,uk.tech.digital-tv
F Murtz
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Posts: 6
Default projecting an image

Dave Farrance wrote:
Bill Wright wrote:

I need to project or otherwise place an image on a wooden board so I can
paint it on the board by using it as a guide. I don't have an overhead
projector. I have some transparent media for a laser printer and I have
a 60 year old 6cm projector in the loft but I don't want to dig it out
and the bulb will blow and the whole thing will be annoying.

Isn't there some way the old painter guys used to do this, just with a
mirror or something?

Come on gentlemen and ladies, ideas?


How big a board? If it's not too big, goto Youtube and search on "print
on wood" or "photo to wood" and look at the tutorials for DIY
inkjet/laser print transfer to wood, which might save you having to
paint the image at all.

Or use a photo editor to do an edge-detect on the image to save ink,
then print to a mosaic of paper sheets that you tape together, tape it
to the board, then trace all the edges onto the board with a needle or
scratch-awl. Remove and paint.

the old boys used to lay a grid over the pic, say 1/2"squares then make
larger grid over the pic to be painted and hand copy each square.

http://www.howtodrawjourney.com/grid-drawing.html
  #30  
Old April 4th 15, 08:52 AM posted to uk.d-i-y,uk.tech.digital-tv
The Natural Philosopher[_2_]
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Posts: 605
Default projecting an image

On 03/04/15 22:11, [email protected] wrote:
On 03/04/2015 20:13, michael adams wrote:
"Norman Wells" wrote in message
...
"Bill Wright" wrote in message
...
I need to project or otherwise place an image on a wooden board so I
can paint it on
the board by using it as a guide. I don't have an overhead
projector. I have some
transparent media for a laser printer and I have a 60 year old 6cm
projector in the
loft but I don't want to dig it out and the bulb will blow and the
whole thing will be
annoying.

Isn't there some way the old painter guys used to do this, just with
a mirror or
something?

Come on gentlemen and ladies, ideas?

You need a lens from an old 35mm single lens reflex camera. Mount
it, eg in a hole
through another board, so you can securely position it where
necessary between the
well-illuminated original and the target board so as to form an image
on it of the
right size.

You may need to darken the room, especially if the image you want is
large.


The resulting image would be upside down and reversed left-right.

That's where all the mirrors, prisms and all the rest of the
tricky stuff comes in.




Like rotating it 180 degrees?


No.
reversing it front to back


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. – Erwin Knoll
 




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