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Does anyone know how to make an Overhead Projector? Answered

Hi All, does anyone know how to make an OHP (just to be clear "OHP" not "OAP" - I already have a couple of these and despite their age they work perfectly well). i'm no artist (nor nuffink), but i'd like to paint an intricate image onto a large canvas. i've mocked the image up on paper, but to ensure accuracy, i'd like to project this image on to the canvas and trace from that. i'm unable to link my computer to an OHP device for all sorts of dull reasons (that neither you, nor i would want to go into right now), so unfortunately this isnt an option. all (practical) ideas will be gratefully received. regards Rens



6 years ago

Do what Leonardo Da Vinci had to do.

First divide your drawing into four quarters and reproduce each quarter by squaring off the original and enlarging it four times on to the respective quarter of your larger paper. Then pin prick all over the lines of your blown up reproduction and with a pencil transfer your pinpricks four times larger, on to the wall by poking the tip of the pencil through each pinprick. then join the dots on your new four times larger surface.

Squaring off means covering your drawing with vertical and horizontal lines then doing the same on a blank sheet but with four times (or however large you want to make it) the distance between the lines.

your link there is worrisome - I wouldn't want the general public to have access to my 'to do' list at work....


10 years ago

thanks for all your suggestions...i think the best idea (assuming it's not feasible / affordable to make my own OHP)is to try and loan one from a school...better get moving quick as they'll be closing for summer soon ("summer"!?! given the weather in the UK this term is surely in violation of the trades description act...if anyone happens to be speaking to the almighty one over the next couple of days, could you mention it on my behalf?) shame about the OHP...i was looking forward to the prospect of toiling away on this...guess not everying in life is Instructablisable.

If your "master" is on paper, you don't need an OHP, you need some kind of camera obscura or camera lucida.

The obscura uses a lens to project an image in a large box or room (like a giant pinhole camera. Put your canvas on the "wall" of the box and brightly-illuminate your master opposite the lens.

The lucida uses mirrors to overlay the image of your master over your view of your canvas. All you need to do is trace around what you see.

sorry to be a dullard, but does this work even when the image I'm starting from is smaller than what I'd like to scale it up to? i.e - the mock up is probably 1/4 of the final size.

sheeeshkebabs!! I will need a really large mirror, glass panel & box to do this as the final canvas size is 720 x 1680mm (assuming i haven't misunderstood the useful link you sent) I'm kinda hoping that i have misunderstood something, as i'd like to give it a go, but before i do...given the canvas size (720 x 1680mm), will i need to scale up the materials accordingly? many thanks for your help on this one.

The box can be a room or tent... ... actually, thinking about it, it would be easiest to re-draw the image onto an acetate sheet and then borrow a projector from a local school's art department.

I've heard that libraries sometimes have them to loan. Once the bulbs burn out they might not replace them. 720mm ~ 24 ft? Too big to use a copy machine and graphite paper?

> ahem <

1000mm = 1metre

720mm = 30 inches

1680mm = 70 inches

(I ought to make a sarcastic comment about metric vs imperial measures, but it's too early in the morning)

Thank you. That's why I was "thinking out loud". I didn't think I had it right. Once I learned about metric I don't understand why we do it the hard way except for it's hard for us old folks to learn to think in a different way. We want to "translate". And I never understood why anyone would use pounds and pence instead of dollars and sense. That means that depending on the detail of the image tiling and tracing is still reasonable. Print the image on multiple sheets at home or at a Kinko type store, draw a grid on the canvas and trace. I can do algebra and geometry but I have problems with measurements and division and multiplication. I was sick a lot in 1st and 3rd grade. Missed the drills. After I graduated from high school they came out with those new fangled electronic pocket calculators for about $150. They helped me a lot since most of my mistakes were in the arithmetic rather than the understanding.

I've no idea what an "OAP" is I assume a joke. what you need is an opaque projector, contact a local school teacher and see if you can use one, probably have to do it onsite. Lot's of schools have replaced opaque projectors with ceiling mounted cams and lcd projectors.

OAP = Old Age Pensioner.

"An elderly person receiving their state pension"

(Yes, in the UK there are still the last vestiges of a Welfare State)