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Pinhole projector help


jonathan

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I've made a pinhole projector out of a carpet roll tube which is about 8' long.  I made a small window in the bottom end, added the white platform for the projection in the bottom, and covered the top with a small patch of tin foil with a hole in it.  I have tried pointing it at the sun so that the shadow is at its smallest but I cannot get a projection of the sun on the white plastic surface I put in the bottom, what am I doing wrong?  The only thing I can think of is that the projection is too dim and cannot be seen, if that is the case then what is the answer?  I'm thinking maybe I need more shade around the viewing window, or maybe I need to use paper instead of white plastic to project onto (can't see why though - white is white).  Any pinhole projector experts here who can advise please?

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4 minutes ago, jonathan said:

 what am I doing wrong?  The only thing I can think of is that the projection is too dim and cannot be seen, if that is the case then what is the answer?  I'm thinking maybe I need more shade around the viewing window,

Shade I think.

I have projected 20 and 30 ft down a corridor in my house and it does get very dim very quickly, so I can imagine 8ft outside would be a problem.

I had to close all doors etc and let the beam in through just a crack to see a 4inch and larger disk.

It did show the transit of Venus, some years ago, very well ! :) and sunspots a treat ! Oh yes, and the '99 eclipse :)

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19 minutes ago, jonathan said:

 correct hole size, I thought the smaller the better?

'Optimum' hole size, yes down to a limit set by Rayleigh, or was it Airy ? I always got them mixed up and it has been a while !

Depends what and how much you want to see, can be quite large to give a bright image to see a partial eclipse, somewhat smaller to see large sunspots and limb darkening and down to Rayleigh in the limit in a dark room for anything smaller. But till you can see something and get things lined up I would not go for the smallest you can make, yet !

 

 

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Sun spots?  I thought 8' would be big enough for that, it's about as long as I could get for a tube.  Failing sunspots then partial eclipse would be good, although I have a proper solar scope so the tube would be for an alternative view / just for fun.  Maybe I need to consider some optics as well to increase the size of the projection?

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This is apparently what you need! A kind of cardboard Virtual reality headset but using the latest pinhole technology ;) 

IMG_6535.JPG

EDIT The same article mentioned that the size formula was the projection distance in feet/9 equals the image size in inches. So you should get just under an inch diameter, does that sound right?

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7 minutes ago, Stu said:

This is apparently what you need! A kind of cardboard Virtual reality headset but using the latest pinhole technology ;) 

IMG_6535.JPG

Ha!  Yeah, I made one of those for the recent eclipse, the small image of the sun wasn't nearly as big as in that picture and it was a box about that size.  But the darkness inside the box is probably what I need to aim for... some sort of enclosed viewing scope like Spock uses on the bridge in the original series.

 

Just one question - do I need to style myself on Fred from Scooby Doo?

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