cheapest basic 8X10 lens

[Bill Backhouse]

I am building a right angled camera obscura thing at work on thursday, basically it will be as follows:

square wood box
pin hole in the 'front' side
mirror internally at 45deg
opaque perspex (ground glass effectively) top

the idea being you point it at your subject, stick a bit of paper on the top and a dark cloth over your head and you can copy the scene onto your paper. it has to be quite portable.

I guess the internal optical length will be about 20-30cm so I'm looking for a cheap lens in that kind of length to substitute for the pin hole to give me a brighter image.

any suggestions, the budget is very limited, they are moaning at £10 for the mirror I'm wondering about things like tescos reading glasses or trying to blag a single lens from specsavers in town etc (I think i need about a +4 dioptre lens).

any help or suggestions?

[Neil Barnes]

I'm thinking big magnifying glass. Or even one of those fresnel sheets - they come in A4 size for a couple of quid: http://www.ebay.co.uk/itm/Fresnel-Page- ... 2eb6511c20

Neil

[Bill Backhouse]

not sure how well the fresnel sheet would work, but I like your thinking.

Your certainly in the right area budget wise I've tried a couple of cheap magnifying glasses and most seem to have too shorter focal length at around 150mm, hence my thought at a lens from some reading glasses.

[dennis]

It will have to be tracing paper on top? Have you read the Hockney book on the old masters useage of lenses & mirrors - can't remember the title? Sounds similar. Dennis

[Neil Barnes]

Just tried a smaller 3.5" * 4.5" fresnel I have lying around (from the same supplier I pointed to) and it's focal length is also about six or seven inches. It's a very bright image, though...

[Andrew Plume]

Hi Bill

magnifying glasses are the way to go - having said that I've only seen published images on a 4x5, however

now if you're after interesting unusual good quality glass, then the Surplus Shed is well worth checking out - here's the link - http://www.surplusshed.com/

regards

andrew