how to workout macro projection distance

[robinb]

Hi

I would like to project onto a wall to get a very large macro image but am having difficulty
with the math
I have held a lens up and got an image just by luck but now trying it again i can't get a big image
how do i work out the object to lens to wall ?
if i was using an actual view camera then i would just go for maximum extension then then
move the whole camera in to the subject with my head under a dark cloth but because of the scale involved
this is not possible

I plan on fixing the lens on a standard and rail for fine focus in a doorway then blacking out around it
then going out the front of my house and around to the back to get to the image
but i just need to work out the basic distances to start with
i have a few long apo ronars that should be good for this but there is probably only a millimetre between sharp and totally out of focus ...
i know i will need a lot of light which is not a problem and would need time let my eyes to adjust in the dark side to see the image

robin

[Charles Twist]

Hello Robin,
I am guessing that the thin lens rule will get you under way. Not sure though.
Regards,
Charles

[Emmanuel Bigler]

Even if you solve difficulties with the maths, you could get into trouble finding enough light to project a very large-size image of a tiny object.

Projecting opaque objects to an audience was done in the past with a dedicated projector named, in France "Episcope". usually the projections were not very bright, and the bigger the image, the darker.
Those devices still exist a new items, see for example the Braun Paxiscope XL, covering about 15x15 cm in object size.

Projecting transparent objects of microscopic size is easier, you need a short focal length as the projection lens and a light source focused inside the projection lens with an auxialiary condenser lens. Exactly like an enlarger, for which apo-ronars make excellent projection lenses, but they are not very bright. Apo Ronars open only a f/9, whereas projection lenses open as large as f/2.8 or 3.5.

[probably off-topic ?]
It might sound provocative to invoke here some digital technology, but in order to projet a small-size objet to a large audience, a small digital video camera combined to a video-projector acts as a very powerful image intensifier. You no longer need to "burn" the objet under a powerful light, only available light is sufficient in order to get a visible "video-projected" image for a large audience.
The best example I have in mind of such a public demonstration, direct projection of images of tiny objects, is done on a regular basis at our local watch & clock museurm ; a retired watchmaker demonstrates in front of the public how to disassemble and re-assemble a mechanical watch. "Live". No computer. No software, no 3-D simulation. No cheating allowed. The most spectacular part of the show comes at the end, when the craftsman liberates the tiny barrel spring; the tiny untamed beast jumps, everybody thinks that there is no hope to re-assemble the watch, but the magician carefully rewinds the spring with a secret watchmakers's tool, and re-introduces it inside its tiny round box! Thrilling !:

[robinb]

Hi Charles and Emmanuel

thanks for your replays

I plan on projecting still life onto 4 sheets of 20x24

I have a huge amount of light so it should all be good

robin