Today I started designing the housing for my cameras in SketchUp. However, I got slightly sidetracked and ended up researching the history of the camera instead. No matter.
While trying to calculate the angle of the field of view, so that I could cut out a conical hole in the side of the box as opposed to a cylindrical one, which would allow for total stability while maintaining complete viewing angle, I found out some interesting things about cameras that I didn’t know before. It all started with trying to work out this angle, which I later found out to be the “Angular Field of View”, or AFOV for short. The formula for working this out is:
This seemed easy enough, so all I needed to do was to find out the sensor width and the focal length of the camera who’s AFOV I was trying to calculate. However, instead of Google’s search results bringing clarity, it made matters more confusing, as the results for the Canon PowerShot SX500IS were as follows:
Full model name: Canon PowerShot SX500 IS
Resolution: 16.00 Megapixels
Sensor size: 1/2.3 inch (6.2mm x 4.6mm)
Lens: 30.00x zoom (24-720mm eq.)
So I deduced that the sensor size 6.2mm x 4.6mm, as those were the values in the brackets, but I had no idea what the “eq.” meant for the focal length. Also, I had no idea what the 1/2.3 inch meant.
I started with the lens’s “eq.”, as I needed to find out if that was the actual focal length or something different. I found out that it meant is was the equivalent to 35mm film. Another search and a Wikipedia page soon lead me to the understanding of 35mm film equivalent. Basically, back in the days when film was still used, Kodak came up with the 35mm film in 1934 and it grew in popularity until it overtook the standard 120mm film. 35mm refers to the actual size of the film tape, with each of the images on the film being 36mm x 24mm… But there is no 35mm anywhere in those dimensions! I later found out that this because the height of each image is 35mm, inclusive of the sprocket holes on either side of the 24mm height.
35mm film was taken on cameras with a sensor size of 36mm x 24mm (which is why that is the size of the images). This was called a “full frame” sensor and was what pretty much every photographer and cinematographer used, so it became standard. Later, when the CCD sensors came into play, the size of the sensor got reduced drastically, allowing for smaller cameras. Since the standardization was no longer being used and new and smaller sensors were taking over, the lenses for the sensors were being altered as well. This meant that the actual length of the lens would vary from camera to camera, which all were taking the same photo. In order to bring some kind of standardization back, a “crop factor” was created. This calculated how much the 35mm sensor sized was “cropped” with the new sensor due to its smaller size. If the sensor size was half that of the full frame sensor, then the crop factor would be 2, meaning that if the lens length was 12mm on the smaller sensor, it would be a 24mm equivalent if being used on a 35mm full frame camera. The use of equivalence brought back standardization to an industry where nothing was standard. It was a way to get people to understand what they were buying without complicating matters and selling them something they were familiar with.
Now this was starting to make sense…
My camera had a 24-720mm equivalent lens, meaning that if I was too shoot the same shots on a full frame camera, the actual lens length would be that big.
Next it was time to look at the whole 1/2.3 inch sensor size nonsense. From what I learned when exploring the lens equivalent meaning, I came across the reason for using inches in the size of the sensor, which is for a historical reason:
Before digital image sensors they used video camera tubes. These used cathode rays to record the light that was entering the front of the tube, which was the lens. The common 1” circular video camera tubes had a rectangular photo sensitive area about 16 mm diagonal, so a digital sensor with a 16 mm diagonal size was a 1″ video tube equivalent. (I know, they’re mixing metric and imperial. It’s wrong. So very wrong). Since nowadays’ diagonal sensor sizes are much smaller than 16mm, they should be denoted as a fraction. Which they are. An 8mm diagonal sensor is called a 1/2″, which is a half of the 1” historical cathode ray tube lens size.
However, a 1” diameter is 25.4mm, not 16mm. This is because it was worked out that of those 25.4mm, only 16mm was usable. This was then applied to newer sensors that were made and the ratio stuck. Sort of. The camera companies didn’t stick exactly to this ratio, but a more rounded off number, making it rather confusing for anyone newbie in photography who didn’t understand and had been through the history of the camera.
Now that I understood why that was a thing, calculating the angular field of view became a lot easier. I also knew how to calculate the crop factor, which would allow me to calculate my actual lens size and not the 35mm equivalent. Since I knew the size of both my cameras and the 35mm’s sensor, it was easy to calculate the diameters. Once I had the diameter of the 35mm, I divided it by the diameter of my camera to get a crop factor. This worked out to be around 5.64x. My sensor was 5.64 times smaller than a full frame sensor, meaning that if I divided the lens equivalent by that, I would get my actual. This turned out to be surprisingly accurate and I calculated the lens to be 4.1mm, which was correct.
With this I was able to calculate the angular field of view, which allowed me to continue designing the box in SketchUp.
Today was interesting, as I was taking a seemingly remote subject to my project, and found a link that enabled me to learn more about something that I would otherwise have never learned about.
I will restart the housing design tomorrow, as the first version was a fail and I actually need to come up with an action plan before I get started.
