projecting an image

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

Like rotating it 180 degrees?

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.

It makes no difference. A 50mm focal length lens will make a 1:1 image at 100mm either way around.

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

Sounds like you need a sign writer then. Brian

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

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.

No. reversing it front to back

Not so. If the focal length is 50mm, what that means is that light from any infinite point striking it will be focussed 50mm the other side of the lens. You think the image is just 1" x 1.5" simply because that is the size of the film you place at that distance. If you placed a bigger bit of film there, the whole of the film would capture the image, but it would cover more of what is visible to the lens.

To get a magnified image, as with a magnifying glass, the object you want to magnify has to be within the focal length, and the closer it is the larger the image produced. You must know that from experience.

All you need to know are the schoolboy optics formulae:

where u is the object distance from the lens, v is the image distance from the lens, and f is the focal length

and

magnification = -v/u.

See for example:

You've probably now read what Norman explained. If in doubt, think of this in terms of opening the back of a camera and placing the picture you already have where the film would normally go. Illuminate this picture and it will make at image at the distance you can set using the camera's focus control. i.e. ant any distance from its minimum setting up to infinity.

Then consider using the lens without the rest of the camera to make it easier to illuminate the picture you have, etc.

Jim

The problem with that is that chinagraph is wax based and you end up with wax residue on the surface you want to paint. The art technique is pouncing - prick holes along all the lines you want to transfer, fix the image over the surface to be painted, then force chalk or graphite dust (depending upon the background colour) through the holes by placing the dust in a muslin bag that is banged (or pounced) over the prick marks.

The large camera obscura in Edinburgh uses lenses.

Toys R Us for a working toy projector. I think I've seen a toy epidiascope somewhere too.

Or cardboard box around a monitor with a suitable convex lens.

Cheers

But that isn't what's needed.

Actually it is...

More than that, I suspect. All I know is that French Daguerreotype images which were direct were upside down and reversed left to right. The upside down bit was solved by rotating the image

michael adams

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Of course it does, just imagine lying on your side then its upside down and is fixed by rotating it 180 degrees.

Put an apple in your right hand pocket. Turn a cartwheel 180% degrees so you're balanced on your hands upside down.

Before it falls out in which pocket is the apple ?

michael adams

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