projecting an image

[Bill Wright]

No I think that because lens design gets increasingly difficult if the size of the area covered is bigger. Distortion gets worse. So a modern lens is designed with accurate coverage restricted to not much more than the intended target size.

If you placed a bigger

Only within limits. The optics would give out completely beyond a certain point.

but it

So it boils down to what I said, which is that if you want a focussed image from an object that is effectively near infinity using a lens with a focal length of 50mm the surface on which the image is to form has to be 50mm away from the focal plane of the lens. Since I need an image 600 x 600mm, placing the surface on which I want the image to form 50mm from the focal plane of the lens will result in the lens having grossly inadequate coverage. In practice for a normal compound lens designed for a 35mm camera you'd get a circular image about 100mm across in the middle of the 600mm x 600mm surface.

Bill

[Bill Wright]

Yes you could do it that way round. It would just amount to using the camera as a 35mm projector. The original is actually quite big though. Almost life size. I suppose I could make a very small copy of the original, but then I might as well dig the projector out of the loft, which I was trying to avoid.

That isn't what Norman explained by the way.

Bill

[Norman Wells]

If you place the original, well-lit, within the focal length of the lens, and preferably as close to it as possible, then you will be able to get a complete image of it at whatever size you want on the medium on which you want to reproduce it. The further away from the lens you place the medium, the larger the image will be, though of course correspondingly fainter.

If you don't understand the theory, just try it.

[Bill Wright]

Sounds as if I understand optics a lot better than you.

Bill

[Bill Wright]

I've decided to do it with a grid. So far it's going well. I have a 64 x

64 grid on the original and the same on the board, but scaled up 8x. It isn't much harder to copy onto the board than it would be to draw round the picture elements (having cut them out).

I've done the head but I decided to leave the teeth. I might put some yellow on them. I'm going to do the eyes last, in red. As for the bones, well I like the idea of two femurs rather than the rather bland generic bone shapes that are traditional. The offset heads of femurs are rather cute I think.

Bill

[Norman Wells]

Well, I admit I was wrong in some respects, but not as wrong as you think. With a single convex lens, the object actually has to be positioned at a distance from the lens of greater than its focal length in order to form a real image that can be captured on the medium you want to copy onto. To obtain an enlarged image, the object has to be between the focal length and double the focal length away from the lens.

If the focal length of the lens is 50mm and you position the object at, say,

60mm from it, you will get an in-focus image formed at 300mm on the other side of the lens, and the magnification will be 5 times.

[spuorgelgoog]

Painted on the side of the shed, that should keep the JWs away.

Owain