Is this normal or am I doing something wrong?

rpavich · Dec 12, 2017

I just upgraded my pinhole shoebox camera by getting another piece of coke can and putting a smaller rounder hole in it and sealing up the edges around the lid.
I took it out and took a shot of a local hospital. I guessed at the time, my neg came out REALLY dark. (paper negative 7 x 10)

My problem is this; why is the middle lighter than the edges and is this normal? Is the paper just too big?

Also, I measured the pin that I used to punch the hole and it measured at .023 at the widest part. That's .58mm Wow...and I thought I made a really small hole. It's 4.5" from the shutter to the film plane, is there a calculator that I can use to calculate the f/stop from that?

Also, Is that large size aperture going to be a problem too?

DWThomas · Dec 12, 2017

You are working at a fairly wide angle, and fall-off away from the center axis is a normal thing. Not sure why, but I have felt it's more noticeable with paper than with film, which doesn't make much sense.

There is a site called Mr Pinhole that has all sorts of information and calculators. I actually prefer Pinhole Designer, a program that you download and install under Windows, as Mr. Pinhole is a little short on explanations as to what assumptions are made, but the Mr. Pinhole stuff runs web-based via scripts, so it's much more universal.

MattKing · Dec 12, 2017

rpavich said:
why is the middle lighter than the edges and is this normal

The edges are farther away from the pinhole than the centre is, so the paper negative receives less exposure at the edges. This is normal.

rpavich said:
Also, I measured the pin that I used to punch the hole and it measured at .023 at the widest part. That's .58mm Wow...and I thought I made a really small hole. It's 4.5" from the shutter to the film plane, is there a calculator that I can use to calculate the f/stop from that?

.023"/4.5" = 1/196 - therefore your f/stop is 1/196.
The two programs suggested by Dave can help you choose an optimized pinhole size. If I am using it correctly, Pinhole Designer recommends a pinhole size of .019 inches, which would yield an f/stop of 1/237 (using the Lord Rayleigh constant).
For comparison purposes, my fairly well optimized Noons 6x12 pinhole camera offers a 60mm focal length, and an f/stop of 1/207.

DWThomas · Dec 12, 2017

Some further comment about fall-off. Not only is the pinhole-to-film distance increasing as you move off-axis, there is also the problem that a circle viewed at an angle becomes an ellipse so the effective aperture area is shrinking. At 90º off axis, the pinhole appears closed. So there is an exponential decrease in exposure due to those combined effects.

An additional problem can be in the actual fabrication of the pinhole. The ideal pinhole has a perfectly round knife sharp edge and is made in an infinitesimally thin sheet -- a rather impractical situation! In an extreme opposite case, where a hole is drilled in a relatively thick plate, the fall-off is much more rapid and will produce a vignetted image. It's fun stuff and in the end, sort of comforting to get a recognizable image with so little technology.

rpavich · Dec 12, 2017

DWThomas said:
You are working at a fairly wide angle, and fall-off away from the center axis is a normal thing. Not sure why, but I have felt it's more noticeable with paper than with film, which doesn't make much sense.

There is a site called Mr Pinhole that has all sorts of information and calculators. I actually prefer Pinhole Designer, a program that you download and install under Windows, as Mr. Pinhole is a little short on explanations as to what assumptions are made, but the Mr. Pinhole stuff runs web-based via scripts, so it's much more universal.

I just found it. Thanks!
I guess it looks worse by having a 10" wide piece of paper in the box, If I were only looking at a 4x5 then it would seem a LOT more uniform.

MattKing said:
The edges are farther away from the pinhole than the centre is, so the paper negative receives less exposure at the edges. This is normal.

.023"/4.5" = 1/196 - therefore your f/stop is 1/196.
The two programs suggested by Dave can help you choose an optimized pinhole size. If I am using it correctly, Pinhole Designer recommends a pinhole size of .019 inches, which would yield an f/stop of 1/237 (using the Lord Rayleigh constant).
For comparison purposes, my fairly well optimized Noons 6x12 pinhole camera offers a 60mm focal length, and an f/stop of 1/207.

Very interesting. So your Noon 6x12 is actually much closer from pinhole to film than my box. I was looking at those, they looked nice.
Thanks for the math help, that answers the exposure question

DWThomas said:
Some further comment about fall-off. Not only is the pinhole-to-film distance increasing as you move off-axis, there is also the problem that a circle viewed at an angle becomes an ellipse so the effective aperture area is shrinking. At 90º off axis, the pinhole appears closed. So there is an exponential decrease in exposure due to those combined effects.

An additional problem can be in the actual fabrication of the pinhole. The ideal pinhole has a perfectly round knife sharp edge and is made in an infinitesimally thin sheet -- a rather impractical situation! In an extreme opposite case, where a hole is drilled in a relatively thick plate, the fall-off is much more rapid and will produce a vignetted image. It's fun stuff and in the end, sort of comforting to get a recognizable image with so little technology.

That's very interesting! There's a lot more too this than just banging a hole in some metal and throwing a piece of paper inside, however I'm pretty thrilled that I got this far and with a slight bit of improvement of my hole and cutting down my paper, it will get better.

Theo Sulphate · Dec 12, 2017

Just for reference, the Zero Image 2000 (6x6cm format) has these specs:

- pinhole size: 0.2mm, f/138
- focal length: 25mm
- image circle: 87.5mm

I'm not sure, but they may use a laser to punch the hole through the very thin metal membrane that is the shutter.

rpavich · Dec 12, 2017

Theo Sulphate said:
Just for reference, the Zero Image 2000 (6x6cm format) has these specs:

- pinhole size: 0.2mm, f/138
- focal length: 25mm
- image circle: 87.5mm

Thanks, that does give me something to think about and gauge my own efforts.

MattKing · Dec 12, 2017

rpavich said:
There's a lot more too this than just banging a hole in some metal and throwing a piece of paper inside,

Actually, that is part of the fascination of pinhole.
If you do that, it still works!
And yet, there is lots of room to refine too.
Colour can be fun as well
(Noons pinhole set to 6x9, Ektachrome 100G):

And to show you even more extreme fall-off
(Noons pinhole set to 6x12, T-Max 100):

Caution - pinholes are both fun and addictive.

rpavich · Dec 12, 2017

MattKing said:
Actually, that is part of the fascination of pinhole.
If you do that, it still works!
And yet, there is lots of room to refine too.
Colour can be fun as well
(Noons pinhole set to 6x9, Ektachrome 100G):
View attachment 191777

And to show you even more extreme fall-off
(Noons pinhole set to 6x12, T-Max 100):

View attachment 191778
Caution - pinholes are both fun and addictive.

Very nice!

wyofilm · Dec 12, 2017

MattKing said:
If you do that, it still works!
And yet, there is lots of room to refine too.

See pinhole cameras are like Hobbits:

"You can learn all that there is to know about their ways in a month, and yet after a hundred years they can still surprise you at a pinch."

Theo Sulphate · Dec 12, 2017

A Hobbit would have a pinhole camera. I'm not sure what the other denizens of Middle Earth would use, though the Elves probably have Leicas.

MattKing · Dec 12, 2017

Theo Sulphate said:
the Elves probably have Leicas.

No - probably Alpas

tezzasmall · Dec 13, 2017

I quite like the fall off effect with pinhole pics. Could it just me...?

Terry S

Jim Jones · Dec 13, 2017

Most of the fall off effect is also characteristic of equivalent lens and film sizes. The higher contrast of paper in relation to film also makes a difference.
Rpavich, for much information on pinhole photography, look online for a copy of Pinhole Photography by Eric Renner. Also go to https://jongrepstad.com/pinhole-photography/

rpavich · Dec 13, 2017

Jim Jones said:
Most of the fall off effect is also characteristic of equivalent lens and film sizes. The higher contrast of paper in relation to film also makes a difference.
Rpavich, for much information on pinhole photography, look online for a copy of Pinhole Photography by Eric Renner. Also go to https://jongrepstad.com/pinhole-photography/

Thanks.

Is this normal or am I doing something wrong?

rpavich

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