projecting an image

Google 'camera obscura'

Andrew

See if you can find an old epidiascope.

Used to be a lovely old one in my old anatomy lecture theatre.

Tim

Here you go. ;-)

They're very simple "machines". Would make a good DIY project.

Tim

Tim

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

Bill

You don't say what the relative sizes are, but you could scale up the image using grids. Draw a grid on the image and a proportionally larger grid on the board which will show you where the outlines cross so as to keep it on proportion

or lash up a pantograph

using some pieces of timber. Which just needs a two pencil sized holes - one to trace and one to draw, and holes drilled to take the pivots where the arms cross.

michael adams

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Do you know anyone who would lend you the sort of projector that plugs into a computer? If so, you could take a digital photo of the image and then project it from a laptop.

On second thoughts...

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.

michael adams

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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.

michael adams

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Matthias Wandel's brig print makes the printing stuff to real scale easy:

Now that might just work. Definitely worth a try. I can print the original any size I want, so scaling would be easy.

Bill

I discounted this, but thinking again I will ask my IT shop. They are very helpful.

Bill

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

Upside down isn't a problem, and you could mirror the image by taking a digital photo, reversing in software and printing.

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.

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.

Bill

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

Or you could project it onto tracing paper and reverse that.

Providing you could find a big enough sheet of tracing paper that is.

michael adams

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And if you reverse the lens?