pin hole images

[Peaton]

I’ve been messing about with pinhole images for the last few days, and there are one or two things that I am puzzled about. I was wondering if anyone can throw any light on the subject.

Not having either the time or the patience to get involved with film, I used my slr digital body, The first trial was just a piece of black card taped over the lens opening with a pinhole in it. I obviously didn’t get the pinhole dead centre as one side of the image is blank, ( image 1 ). I had to mess about with iso and timer settings.

The next time I used the body cap, I drilled a 1/8 “ hole dead centre, the marks in the plastic moulding helps with this, I then cut a small piece out of the side of an aluminium drinks can, sprayed it matt black and put a tiny pin hole dead centre, and glued it to the inside of the body cap.

What’s puzzling me is:- the images are very much softer than I expected, massive DOF though. This softness could be normal though, never having tried this before.

The main puzzle though is, there are marks on the image that initially I took to be dust on the sensor, I have since proved this, not to be the case. After much thought and experimentation, From the shape of the marks ( after blowing up ), I was wondering if they could be reflections of the pin hole itself, bouncing around on the inside of the camera body.

The first piece of aluminium was 5 thou thick, and I was wondering if the marks ( rings ) were caused by the thickness of the metal, being shiny at the edge of the hole, so I tried a piece of kitchen foil, only 2 thou thick, no difference whatsoever. But the original was cardboard and the rings were still there, so this reasoning can’t apply to this.

I know everything seems to point to dust on the sensor, and there is just one speck, but it is not the same as the others, it is minute, and only shows up at 200% magnification.

I have now run out of ideas, so any suggestions, or ideas would be most welcome. Then I may be able to get out and try using it on some more interesting images.

Regards

Peter

image-1.jpg (58.68 KiB) Viewed 5029 times

[John]

The softness is normal, but the larger the pinhole the softer it will be.

The best way is to use very thin brass shim, press a needle into it so it causes a protusion but doesn't quite go through. Then gently rub the protuding bit with fine emery paper until the hole is just made.

The distance the hole is from the film/sensor will change the focal length.

Hope that helps!

[Peaton]

Thanks John, will have another play tomorrow and try that out.

Peter

[TerryMooney]

Peter - Last week I was doing the same experimenting that you have done - I connected a bellows unit to the front of my Canon 5D and used a 5 thou. thick black card disc with a 0.78mm dia. pinhole and set the focal lenth to approx. 220mm.
Exposure was 30sec. Took a photo through kitchen window.
Examing the result at high magnification my photo has lots of the same doughnut like images just like yours.

I've looked on the internet and found this article(slightly editted by me).

"Each point on the surface of an illuminated object reflects rays of light in all directions. The pinhole camera lets through a certain number of these rays which continue on their course until they meet the projection plane where they produce a reverse image of the object. The point is not reproduced as a point, but as a small disc, resulting in an image which is slightly out of focus. The size of the small disc is dependant on the size of the pinhole and of the distance it is from the projection plane (the focal length). The whole image is made up of hundreds and hundreds of overlapping discs."

So the question is why are some of these discs so distinct?? Also found the discs occurred in greater numbers further away from the centre, especially near the edges.

There is a good website at http://www.pinhole.cz (were you can find the article quoted above)

TerryMooney

[Peaton]

A very interesting article that Terry,
I spent most of the afternoon following one link after another, until I got totally lost and couldn’t find specific parts again. One thing that stands out is that it’s not the smallest hole that’s the best, there is an optimal sized hole dependent on the film to hole distance, the thickness of the plate and the shine on the inside of the hole are also factors. So now I will start to expand this almost invisible hole, and see what I get. It bears out the fact though, that the more precise I've got the worse the images become.

I’m beginning to wish I had never started messin, what started out as an hours play, ended up as a weeks intense study and experimentation ( very enjoyable though ). My to do list has now extended into 2012.

Thanks Terry

Regards

Peter

[John]

You could cheat and buy a pinhole camera kit...but it might not be so much fun.