How to estimate a f/stop on a pinhole w/o knowing the lens.

Tomsmac

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Good day.
I dusted off a long ago purchased pinhole 4x5 and there’s no indication of the lens aperture. Should I just guess at f/22?
Thank you.
 

Dan Daniel

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Too fast. Numbers I have seen are in the f/180-350 range?

And reciprocity is a real issue.

The Comprehensive Tech Guide To Pinhole Photography

If you're somebody who likes to take film photographs, you know the satisfaction you get from a film photo that you just don't feel when you use digital. Just imagine seeing the first photo you get out of a camera you designed and built yourself! The process of designing and building a camera...
www.diyphotography.net
 

Donald Qualls

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With an educated eye and a loupe you can estimate the diameter of the pinhole against a millimeter scale or dial/digital caliper jaws, then measure from the pinhole to the film plane; diameter divided by projection distance is f ratio.
 

MattKing

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I have a friend who uses an enlarger to determine the size. You could also use a slide projector. He projects a known object such as a small sized negative on a wall and then measures the image to calculate the magnification.
He then swaps in the pinhole where the negative was, measures the image on the wall, divides that measurement by the calculated magnification, and that gives him the size.
The aperture results from dividing the calculated diameter of the pinhole by the camera's distance from the pinhole to the film plane.
 

Donald Qualls

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If you have the pinhole out of the camera, a flatbed scanner also works well for this -- lay the pinhole on the scanning glass, scan it, then use editing software like GIMP or Photoshop to count the pixels across the hole and multiply by the known pixel resolution (if, say, your hole is 37 pixels and your scanner is set at 1200 ppi, 37/1200 is the diameter in inches; multiply by 25.4 to get millimeters if preferred).
 

AgX

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Donald Qualls said:
With an educated eye and a loupe you can estimate the diameter of the pinhole against a millimeter scale or dial/digital caliper jaws, then measure from the pinhole to the film plane; diameter divided by projection distance is f ratio.
Click to expand...

A alternative is to use a set of microdrills of known or measured diameter to gauge the hole, but this includes the chance to harm the hole.
 

eli griggs

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Have someone with an accurate analog or digital caliper measure the distance or buy a set of small, oxygen/acetylene welding drills and keeping the cut drill section away from the appature, while using the smooth shaft to see which fits.

THEN, use a good caliper to get the thickness of the shaft, instead of trusting the manufactor's index.
 

AgX

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eli griggs said:
Buy a set of small, oxygen/acetylene welding drills.
Click to expand...

Interesting idea, and cheap. However a set of regular micro-drills goes further down in size, at least to 0.3mm.

One also may start with a set of sewing needles, likelely at hand in any home.
 

Donald Qualls

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AgX said:
One also may start with a set of sewing needles, likelely at hand in any home.
Click to expand...

The hazard of this is that a finely tapered shaft like a sewing needle is prone to enlarge the hole, not to mention making it hard to keep track of exactly where on the needle you need to measure.
 

RalphLambrecht

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Tomsmac said:
Good day.
I dusted off a long ago purchased pinhole 4x5 and there’s no indication of the lens aperture. Should I just guess at f/22?
Thank you.
Click to expand...

All you Youneed to know about the lens is known. The distance from the Pinhole to the film plane is the folk length in the whole diameter is the aperture. It may be difficult to measure the diameter of the piano but admit it's easier if you look at it under a microscope or project it with your larger add a known magnification and then measure the projected image.
 

Donald Qualls

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Autocorrect much, Ralph?
 

AgX

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Donald Qualls said:
The hazard of this is that a finely tapered shaft like a sewing needle is prone to enlarge the hole, not to mention making it hard to keep track of exactly where on the needle you need to measure.
Click to expand...

Seemingly american needles are different from german ones in their design.
 

Donald Qualls

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AgX said:
Seemingly american needles are different from german ones in their design.
Click to expand...

Even if there's a straight shaft (and there usually is, here) the long taper to that shaft is the issue. Not to mention the small number of available sizes.
 

AgX

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Donald Qualls said:
Even if there's a straight shaft (and there usually is, here) the long taper to that shaft is the issue. Not to mention the small number of available sizes.
Click to expand...

Let the needle glide on its own weight through the hole, caring that the needle will be stopped at its point before the eylet reaches the hole.
Yes the number of needle sizes is limited, but to about same number as nozzle-drills. Moreover with nozzle-drills you likely first will have to cut off one end. End you still got no tapered end facilitatin entering. Same as with micro-drills, but here at least you got the largest assortment.
 

MattKing

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reddesert

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Lay a ruler across the pinhole and use a magnifying glass and cell phone camera to take an enlarged picture. It may help to illuminate the pinhole from behind at a glancing angle with a flashlight or similar.

Pinholes are usually somewhere between 0.2mm - 1mm, you don't need an incredible degree of precision.
 

Donald Qualls

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reddesert said:
you don't need an incredible degree of precision.
Click to expand...

This is key.

If you're off by 30% under or 40% over, you're only one stop off either direction, and negative films generally have more latitude than that. Anyone can do better than this, reading the size against a suitable fine scale. You'll often find you have to make more adjustment than that for your combination of film, developer, developing technique, etc.
 

NedL

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+1 not rocket science. If you hold the pinhole up to a ruler w/ mm markings on it, you can estimate close enough w or w/o using a magnifying glass.
 

VinceInMT

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I’ve used the sewing needle method. I use needles of various diameters and drop them into the hole with only their own weight, not pushing them. When I find one that won’t go through, I mark the shaft with a Sharpie and then read the diameter adjacent to the mark with a micrometer. A packet of needles of various sizes is very inexpensive.
 

eli griggs

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Tomsmac said:
Good day.
I dusted off a long ago purchased pinhole 4x5 and there’s no indication of the lens aperture. Should I just guess at f/22?
Thank you.
Click to expand...

Stop by a machinist shop and ask them to use a pin gage to test the hole, for a few bucks.

Better yet, order a small, none too expensive, pin gage set, SAE or Metric, and work your way up to the correct size, then sell the set on to someone here that has a similar question, or wants make their own pinholes.

It would be interesting to see how long that one set could be passed alone, but it could also be the bone to pick with later buyers and create needles division amongst Photrio.com, so nevermind.
 

grain elevator

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Why not measure photographically? Take a picture of something with several discreet shades that you measure beforehand at midling exposure time, or make a test strip type of thing timing different exposures on one sheet with the dark slide. (Take a picture with a lens with known f-stops at correct exposure if you need something to compare to.) See what you get - estimate how many steps over or under to determine aperture.
Another idea: a stack of paper, if need be a book, is a fine ruler. You know the thickness of one sheet from a simple division of thickness of package or book by sheet or page number. A magnifying glass or macro lens is all that's needed otherwise.
 
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