How-To: Pinhole Basics

Disclaimer: All the information in this article comes from Mr. Pinhole website, I'm just adding images and a guide to navigate Mr. Pinhole's tools. I think it's important to acknowledge the importance of the information on this website and give all the credit to the person that has created it. 

    Before starting the design of a camera is important to understand some concepts that will help us use Mr. Pinhole's amazing website. I'll try to eliminate math as much as possible, and the easiest way to do it is by using Mr. Pinhole's website. First, we need to understand some basic pinhole concepts. 

Pinhole Concepts  

Focal length

    Focal length is the distance from the film plane to the pinhole. 

    For instance, in this camera, the pinhole is situated on the left side and the film plane on the right. The focal length is 70mm.

Pinhole Diameter

    Pinhole diameter determines image sharpness and the intensity of light falling on the film. Diameters smaller than the optimal diameter may cause unacceptable levels of flare in the picture. Larger diameters allow for shorter exposure times and make pictures fuzzier.

    It is important to know the size of the Pinhole. If you want to know how to measure it, check this article first: How-To: Make a Pinhole 

F/stop

    F stop is the ratio of the pinhole diameter to the focal length(f stop = focal length/diameter). The exposure time depends on the f stop and light reflected from the subject.

    If we know the f/stop number, it is easier to get beautiful pinhole exposures. 

Film Dimension

    Film dimension is the actual image size measured on the film. The value typically used is the image diagonal.

    For instance, in an Instax Mini film is 75mm

Image circle

    The image projected from the pinhole forms a circle on the film plane. The image diameter should be larger than the film diagonal to avoid vignetting. 

    For instance, we already know the Image diameter on an Instax Mini is 75mm. 

    In this example, a 88mm image circle is big enough to cover an Instax mini completely. (88mm >75mm)

    In this other example, a 65mm image circle is not big enough to cover the film completely, so the corners will be black (65mm < 75mm)

Navigating Mr. Pinhole tools.

    To build a basic but robust pinhole camera you just need to understand how to use 2 tools from Mr. Pinhole website, The Pinhole Camera Design Wizard and the Pinhole Camera Exposure Guide. 

Pinhole Camera Design Wizard 

    The easiest tool to start designing a simple pinhole camera is Pinhole Camera Design Wizard (mrpinhole.com)

• If you already have a box or a tin can you want to convert into a Pinhole camera, I would recommend starting by using the focal length. 
• If you have a pinhole, but you haven't decided which box or tin can are you going to use, then start by using pinhole diameter.
• Film dimensions and Angle of view are more helpful when you are designing a camera from scratch (I'm not getting into this amount of detail but I'm willing to help on Twitter if somebody has specific questions) 
  
  *I'll share the details on how to use this tool in the next article.
  
  

Pinhole camera Exposure Guide

    The easiest way to calculate the exposure time is to use the Pinhole Camera Exposure Guide  

    Once you know your f stop you can accurately calculate the exposure time using this tool and a light meter (if you don't own a light meter there are plenty of free lightmeter apps). For instance, if my camera has a f stop 200, I get the following table

*I'll be sharing more details on how to use this information in the last article of the How-To Pinhole series. 

    This article is only intended to understand basic concepts to follow my articles aimed to build and use a Pinhole camera. Also, to show that there are tools that can make our pinhole building process much more easier.

Karin.