Some starter questions

[goros]

Hi all,

I'm thinking in building my own pinhole camera out of a biscuit can and I have several questions about it.

My intention is not to use film, but paper (actually Ilford MGIV RC) therefore, getting a "paper negative". Afterwards, I will get a positive print by contact printing. If I place the negetive print on top of the second paper, emulsion to emulsion, I will get a positive copy but reverse sided (that is, left to right). A solution is to place the negative with the emulsion upwards, then printing through the negative paper. Is there any problem with this way?

Next question: As I will use a multigrade paper as "film", is there any advantage in using a contrast filter just behind the pinhole, to get a fixed contrast? How long a "standard" exposure would be?

Now building issues: Which pinhole size would be more or less OK? I will do it with a pin, so there will not be a lot of accuracy, just to get an idea: 1 mm, 2, 5?

And another one: Once the camera was built, is there any way to calculate the focal length of the hole?

Thinking about all these things, I have an idea that I don't know if it could be practical. The thing is to use a water lens. Just when the pinhole is open to take the exposure, put a small drop of water in the hole. If the exposure time is very long, the water will evaporate but for a exposure of five minutes it could work.

Well. too much for the first time.

Thanks in advance for your help.

Cheers

 

[Ole]

If you make a print emulsion to emulsion, you will get a reversed print relative to the negative. But the negative is already reversed, so you'll get the print the right way.

Pinholes tend to be very small - 0.2mm to 0.8mm or so.

I suggest you read here: Dead Link Removed

 

[goros]

Are you sure? When printing from a neg, it is emulsion-down in the enlarger. If you put it emulsion-up, you will get a symetrical (mirror) image of what you get when it is emulsion-down. The same has to happen with a paper negative.

Thanks for the link. Very interesting and full of tips.

Cheers

 

[Steve Smith]

Think about taking the picture. You are behind the camera. The paper negative is in front of you with the emulsion on the rear. You contact print emulsion to emulsion so in the final print, the emulsion is where it should be - on the front!

Steve.

 

[goros]

In this case, yes. But what I had in mind was to take the picture with the paper emulsion in the front, that is on the paper side nearest to the pinhole, to make exposure time shorter and to avoid getting the paper texture on the image.

Once, when printing a 35 mm negative, I placed by mistake the paper with the emulsion on the "wrong" side, at the bottom. The exposure time was something like two to three times nd there was a pattern on the image showing the paper inner texture. I don't mind to do that, but I would prefer to do it in the printing process (at home) rather than in the taking process (on the field).

Cheers

 

[Steve Smith]

That's exactly what I meant, the emulsion is facing the pinhole. Therefore, when you are viewing the scene, the emulsion on the paper negative is on the opposite side to you. When you contact print it, it reverses so is then correct.

Do it once and you will see!

Steve.

 

[goros]

Well, Steve. First of all, I'd like to thank you and everyone who is reading this thread for the time and efforts you are using to reply me. Really, I appreciate it.

And back to business, yes, you are right. I was all the time comparing it to a 35 mm negative and making the mistake of thinking the emulsion was at the back, not at the front, of the film.

That solves one of my questions. Thanks again.

Regards

 

[BirgerA]

Hi all,

And another one: Once the camera was built, is there any way to calculate the focal length of the hole?
Cheers

I think I've read somewhere that the term focal length is not entirely correct when used for pinhole cameras, but it is normally used when referring to the distance from the pinhole to the film/paper.

Regards

Birger A.

 

[goros]

I think I've read somewhere that the term focal length is not entirely correct when used for pinhole cameras, but it is normally used when referring to the distance from the pinhole to the film/paper.

It should be that, as the focal length is the distance from the lens focal plane to the film and, in this case, the lens is just the hole.

I asked just in case there was another esoteric way to calculate it.

Thanks

 

[Jim Jones]

The diameter of a pinhole is critical for maximum sharpness. Perhaps the best calculator for determining this is http://www.pinhole.cz/en/pinholedesigner/ Measuring the diameter can be difficult. Needles of the correct diameter can be used as a gauge. The pinhole can be scanned and the diameter measured in a photo editor. An enlarger can magnify the pinhole for convenient measuring.

The texture of the photo paper you observed when printing through the base varies widely with different brands. Sometimes it can be distracting. There's little advantage in using a filter with Multigrade paper.

 

[singram]

We build a similar camera in the photo class I teach. We use a mini Pringles can, so the focal length is about as wide as a pop can. This camera is used to teach students that you don't need a $500 camera to make pictures so we don't fuss much about focal length and exact pinhole size. I have found, however, that the push pins with the handle on them, when pushed almost all the way up the sharp end (not big enough for the metal pinhole to slide up the shank of the pin) is a perfect hole size for a 4-5 second exposure and fairly crisp negatives. We use pop cans for pinhole creation, poke 'em and then sand the front and back to get the burrs off. Spray paint the inside of the can, tape over the lid and cut some multigrade paper. Most importantly have fun!

You can change the contrast of the print by using the contrast filters on your enlarger when you project light onto the neg/pos sandwich with multigrade paper. No need for in the camera.

Attached is a photo of a camera my daughter (who was 5 at the time) and I made as well as negative made from said camera.

regards,
steve

[IMGW][/IMGW]

 

[Murray@uptowngallery]

"focal length" is probably the most practical phrase, despite pinhole not being as critical as a lens. One could argue that it is easier to measure for a pinhole camera than figure out exactly where it's measured from on a lens camera!

If you consider any alternative terminology in place of "focal length", they may be arguably correct but raise more questions than they clarify.

The terms image distance and object distance correctly (from an academic standpoint) define the distance from pinhole to film(paper) and item being photographed (subject or object) to the pinhole, but are used less often because fewer people are interested in the physics than are interested in the art.

If better understanding of pinhole results from an occasional cognoscenti utilizing alternative language or discussion about it, then it serves some purpose. Otherwise...not to worry.

Say, that word "cognoscenti" sounds like it should mean "I know that smell" in some classic language, doesn't it?

 

[Joe VanCleave]

Goros, it's best to just jump in and try it! I'd recommend making your pinhole in a thin sheet of brass shim or other metal, and mount it to the tin using black electrical or gaffer's tape, so that you can replace the pinhole if you decide to at a later date.

When I'm building a new camera, I measure the 'projection distance' and then refer to a pinhole calculator for the optimal size. I try to stay with millimeters in measurements, because I usually measure my pinholes using a loupe and a millimeter scale. I place the pinhole next to the scale and back light the hole, then use the loupe to guestimate what fraction of a mm the hole size is. For instance, I recently made a mini 'spy cam' with brass tubing, that had a projection distance of about 1cm. So I figured F/100 was pretty close to optimal. That meant the hole had to be ~1/10 mm in diameter.

The quality of the pinhole - how round and smooth it is - is at least as important as proper size, IMO. So when I'm drilling my own pinholes I will often reject 3 or 4 before arriving at a smooth, round hole near the optimal size.

I like contact printing paper negatives; the image gets reversed in-camera at the time of exposure, due to the optical projection properties of pinhole lenses. Then it gets reversed back to the 'correct' orientation when contact printed emulsion to emulsion. You can also scan the paper negatives and flip horizontally in PS, for quickie online posts.

I like your idea of a water drop lens. Try it, and tell us how it worked. The thing is this: don't ever lose your creative urge to explore new ideas. That's what keeps pinhole fun.

One last thing: try grade 2 RC paper as negatives. Better control of contrast than multigrade.

 

[goros]

Hi Joe,

Thaks for your comprehensive reply.

Of course I will try. As Steves (both of them), Birger, Jim, Murray and yourself have said, I'll just do it (I'm not related to Nike or similar brands) and enjoy it.

Regarding using Grade 2 RC paper, I think I will put a Grade 2 filter at the back of the pinhole and change it according the light conditions.

The water lens is an idea I got from a friend of mine who uses to do macro photography of water drops showing in the drop the scene that was behind. For this purposes I think refined oil will be better than water (evaporation matters). I will let you know.

Cheers