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Although this is offered as a part of the Matchbox Pinhole Project, the technique shown will work to produce accurate pinholes for any camera.

In this post, I will show you a great way to measure the actual pinhole.

You should have a piece of thin metal that will be your structure for your pinhole. In my posts regarding the 120 Matchbox Pinhole Camera I suggest using a small piece of thin aluminum as the material for making a pinhole. Thin aluminum is readily available in the form of aluminum drink cans. Simply cut out a small piece from the sides of the can. In this example, we are using a piece of brass shim. Brass shim can be purchased from a hardware or auto parts store. Either one will do the job.

Before you start poking any hole, it would be a good idea to find out the focal length of the camera. If you remove the lens from your DSLR, you can measure the distance from the flange to the sensor. The way that you do so is by using the image plane indicator mark on the top of the camera. The mark usually looks like a circle with a line drawn thru the middle. The line marks the image plane. If you have your manual, it should tell you where the mark is on your particular DSLR.

Using a metric ruler, measure the distance from the mark to the front edge of the lens flange or at least the back of the camera. In the case of a 120 Matchbox, measure from the front of the box to the rear of the box.  In most cases with a DSLR, that measurement will be somewhere around 40 mm. I will also tell you that the best pinhole aperture for a 40 mm focal length DSLR full frame camera is around .30 mm. You can use almost any size opening, however the optimum size will give you the sharpest image.

Carefully press the pin into the center of a 1" x "1 piece of the aluminum. The pinhole should not be much larger than a tiny point, a small dot or a period. I usually twist the pin back and forth to make the hole as round as possible. If you want to do it properly, there are a few things that will make the pinhole produce better results such as carefully and lightly sanding with a extra fine grit sandpaper and/or rubbing the opposite side to remove the burrs created by the pin. I usually perform this with the edge of a pair of scissors or the rounded end of a spoon handle while being careful to not increase the diameter of the pinhole. You might want to use a black marker on the side facing the camera to blacken the area around the pinhole. I usually blacken both sides making sure that the ink does not fill the pinhole.

To make the best possible pinhole and to help you find the proper exposure, you need to measure the pinhole.  

How do we measure a pinhole? The best way is to make a pinhole in the metal shim and measure it using a scanner.

Step 1 - Lay your pinhole shim onto your scanner platen facing down. Place a metric ruler next to or on top of the shim also facing down.

Step 2 -  Scan a small 3" square area surrounding the pinhole making sure to capture the pinhole as well as a portion of the ruler as in the illustration above. It is best to scan the image at a high dpi. I usually use 2400 or 4800 dpi so that I can blow the image up large enough to read the ruler. There is no need to scan any more than this small area. 

Step 3 - In Photoshop, make a square marque surrounding the pinhole area large enough to capture the pinhole and  a bit of the brass.  Copy and paste the selection into a new layer.

Step 4 -  In the new layer, move the selection to a point over the ruler adjacent to the scales. If you look at the relative size of the pinhole in relation to the marks, you should be able to make a good guesstimate as to the approximate size of the aperture.  Using a millimeter distance on the ruler, visually divide the width of the pinhole into fractions of the distance. between the marks.  In the case above the hole appears to be slightly smaller than a third of a millimeter or .33 mm. I have decided that it is close to .33 mm and because I felt it was slightly smaller, I have decided that the opening will be .32 mm. On a full frame DSLR this equates to an aperture of approximately f /125. Knowing the aperture allows you to calculate the best shutter speed for exposing under different lighting conditions.

Note - It is also possible to measure the distance using the ruler tool in Photoshop. However, you will need to factor in the new scale. I find that the earlier method works just fine. Fudge-factor Pinhole Photography works for me. All I need is to get into the ballpark.

This method of measuring a pinhole works for any type of pinhole camera.

For the 120 Pinhole Project users, save the pinhole until I discuss the method of attachment and discuss a shutter mechanism.

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