F-stop scale

marciofs · May 7, 2013

I am making the holes in a hard black paper. But I will try using aluminium from soda can.

I just made a 0.5mm pinhole. Very close to 0.422mm. I will test tomorrow but I am sure it will be good and sharp.

Thank you all for the information and help. I love it more than my brand cameras.

Now I am thinking about to load 4 sheets of paper in the camera. Maybe place a black thick paper between each of them just to make sure tha the light is not going to get though the first paper and expose the seccond one behing it. Like this I can go to the city or woods, and after each exposure I can put the exposed paper behind of those not exposed yet. Of course I woud do this changing in a change dark bag.

Do you think it woud work? Or any of you have a better idea to reload and take more than one shot without have to go back home to reload the camera?

NedL · May 7, 2013

I think that could work. I sometimes keep envelopes for exposed and unexposed paper in my changing bag and carry it.

I thought of two more things:

1) If you are shooting paper, you can aim to make your pinhole slightly smaller than "optimal" because most of the pinhole calculators use "daylight" and the paper will be more blue sensitive.

2) If you use a little water when you are sanding you can avoid breathing the aluminum dust.

And most important of all: have fun!

marciofs · May 7, 2013

Thank you.

By the way, I am using Ilford MGIV RC Satin and I really like it as paper negative. But I am not sure yet about the ISO. I did the maths all wrong. rsrs.
But I guess it is ISO 25 about.

TheToadMen · May 7, 2013

I rate photo paper normally at ISO 5.

marciofs · May 8, 2013

It's is sharp now:

It is f200, 45sec exposure.

I think the white part was a light leak which I can fix easy.

And as the test show it is ISO 6.

edp · May 8, 2013

NedL said:
I make mine the same way Bethe does: a square of aluminum form a soda can ( you can cut it easily with scissors ) a sewing needle, and emery paper. I use 600 grit paper. I spin the needle with light pressure until it just pokes through, then sand on both sides a lot, then repeat. The hole is always way too small to begin with. It gets bigger as I keep working on it and with some practice you'll get an eye for when it's about right.

Yeah. The needle isn't for pushing through the foil to make a hole, it's for making a bump in the foil, and then you sand the bump off to make a hole. There are several advantages to doing it that way, including: i) the size of the hole is easier to control; ii) the hole is nice and round; iii) it has clean edges; iv) the edges of the hole are thin (this is important if you're making a hole in a thicker kind of foil, like for example a piece of beercan).

I usually use a knife sharpening stone to grind the bump down, because it's very fine grit, it's flat and it's rigid so it doesn't deform while I'm trying to make a nice precise round hole.

NedL · May 8, 2013

Excellent! Have fun!

marciofs said:
It's is sharp now:

View attachment 68466

It is f200, 45sec exposure.
I think the white part was a light leak which I can fix easy.
And as the test show it is ISO 6.

NedL · May 8, 2013

edp said:
I usually use a knife sharpening stone to grind the bump down, because it's very fine grit, it's flat and it's rigid so it doesn't deform while I'm trying to make a nice precise round hole.

This is a very good idea. I'm going to try that. Thanks!

marciofs · May 8, 2013

I tried today a smaller hole. 0.390mm that is smaller the the ideal 0.422 but flare become an issue I think it is because that.

And the image came less sharp than the 0.500mm hole. I don't know if it is because the pinhole is too small or if it is because I loaded three paper in the camera hich moved the exposing paper fowards. Or could it be both?

marciofs · May 8, 2013

Also, is there reciprocity faillure with paper as negative in camera?

NedL · May 8, 2013

I just went back through this thread and I can't find the "focal" length of your camera. But I'd think .39 would be about perfect if optimal is 0.42 for film. Flare can be a problem ( or a feature!! ) any time the sun hits the pinhole directly. I do not think the distance the paper moved from having 3 papers loaded could matter. Maybe there was some light leak around the papers after all?

I ignore reciprocity failure in paper negatives, but have a suspicion it is there in very long exposures. The few times I have made exposures over 10 minutes, the effect has not been as strong as I expected, and I've noticed some strange things that might be different speeds in the different parts of the VC emulsion when the exposure gets over about 10 minutes.

I too would like to know if other people think about reciprocity failure with paper. Or if anyone has noticed this "color separation effect" between greens and blues in long VC paper exposures.

marciofs · May 9, 2013

My camera has 100 focal length.

jeffreyg · May 9, 2013

You might check with your dentist. There are round dental burs that are 0.4mm. Many dental labs have drill press instruments that will hold the bur and make an accurate cut. My original understanding of your thread related to calculating exposure times, if that is a concern the Ilford exposure calculator I described has given me excellent results.

http://www.jeffreyglasser.com/

Jim Jones · May 9, 2013

Using Pinhole Designer with a user constant of 1.4 instead of the default 1.9 and a light wavelength of 500nm, the suggested diameter for a focal length of 100mm is .313mm. The optimum diameter has been argued for well over a hundred years, and isn't that critical for most photography. For macro pinhole photography, the diameter should be reduced even further Dead Link Removed.

I haven't noticed any reciprocity failure in 10 minute enlargements, but any failure might be masked by rather casual evaluation of prints.

As for color separation in pinhole photography, it might be present, although masked by the normal unsharpness of pinhole images. Pinholes do have very slight chromatic aberration.

My technique for making pinholes is similar to edp's. A very hard smooth stone is ideal for the smaller pinholes. For the smallest ones, I keep an ordinary sewing pin in the hole while stoning down the dimple. This gives more control over the pinhole diameter and leaves less of a burr than stoning the dimple without the pin. A sheet of .002" brass shim suffices for many pinholes, and seems to work smoother than aluminum cans. Thinner shim stock is fragile, and thicker shim stock requires more effort to make pinholes with thin edges.

NedL · May 9, 2013

I get 0.34mm and the only difference between mine and Jim's is "user constant" of 1.5 instead of 1.4. I tend to lean toward smaller with paper because blue and uv is usually so strong outdoors. The difference between .31 and .34 might be hard to detect.

Jim, I was not very clear. What I mean is that I've seen an odd almost split-toned effect on some long exposures. I was speculating that it's due to the mixture of different emulsions on VC paper. It's a puzzle: I also have some long exposures that don't show it. By long, I mean 10 to 20 minutes.
This is the most extreme example I've seen: http://www.flickr.com/photos/neds/8430730455

Cheers!

marciofs · May 9, 2013

This two images were taken with a 0.420mm pinhole and the same time exposure 25min.

Do you think the flare is actually UV light. If I use UV filter does it solve this flare problem?

and

And this is from 0.390mm pinhole:

marciofs · May 9, 2013

Jeffreyg,

I am using Ilford exposure calculator and It works very well for me. Thank you.

TheToadMen · May 9, 2013

marciofs said:
This two images were taken with a 0.420mm pinhole and the same time exposure 25min.
Do you think the flare is actually UV light. If I use UV filter does it solve this flare problem

My first guess would be light reflections inside the camera. Did you paint the inside matt black and cover the metal of the pinhole with black tape?
Or did you take the photo into direct sunlight? I supose you don't have light leaks?

Click to expand...

marciofs · May 9, 2013

I don't have light leak.

I covered the metal around the pinhole but a little bite is not covered. Or maybe the larger hole which is curved may reflect the light. I will try to correct it.

Edited:

Actually I don't think there is any reflection inside because these photos doesn't have flare:

and

This flare seems to come from straight sky light, but none of them were direct from sun light.

NedL · May 9, 2013

I don't know. I have seen something like that when the sun reflected into the pinhole. One of my cameras has a 1/4" drilled hole in the side of a can, and the pinhole is taped inside the can. The edges of the 1/4" hole are shiny, and a glint of sun can reflect directly onto the pinhole. It causes something similar.

The exposure in the 2nd one looks very good.

I like UV reflection in the air or mist, but I don't think it could be that strong.

marciofs · May 9, 2013

It is the same then because what you described your pinhole is the same as I have in my camera.

Istead of trying to improve this camera I will make a 7x9in one so the contact prints will be nicer.

Thank you very much for the help. I think I got addicted to it. I just love it.

SMBooth · May 9, 2013

Could you explain the stacking of paper in the camera. Are the image showing the fog from this process. Light will pass through a sheet a paper.

NedL · May 9, 2013

marciofs said:
I think I got addicted to it. I just love it.

It's so much fun, I love it too! There is something very free and liberating and also magic about making a photograph with no lens. The light goes directly onto the paper--- magic!!

You may want to check out http://www.f295.org/main/forum/. It is a great forum with a community of people who love pinhole photography.

Have lots of fun... I predict you will be building one even bigger soon!

marciofs · May 9, 2013

SMBooth,

I put black hard paper between them.
And the last photos I posted I had only the single paper in the camera.

The fog problem is the same as NedL said he had on his one of his camera.

Jim Jones · May 12, 2013

Because pinholes are so small it is easy to improvise a very efficient "lens" hood for them. This should eliminate most flare problems when there is a lot of sky around the subject or when the sun is just outside the picture area.

F-stop scale

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