In today’s blog let us explore one of the things I had the most difficult time understanding. Camera sensors!! I know you are thinking that this is going to be an overly technical article, talking about microchips and photovoltaic surfaces. Yes, I studied physics in high school and No! I am not intending to take you through a physics lesson. I will simplify things and focus on only what you need to know.
What is a camera sensor?
A camera sensor is a light-sensitive surface that is used to capture and record images while taking a photograph. Understanding camera sensors is important as a photographer because camera sensors determine two important things for the photographer. These two things are the field of view and lens choices. Camera sensors have not always been the same. Throughout the history and development of cameras, there have been significant changes since their first recorded use in the 17th and 18th century. Camera sensors in this time had Large format sensors. As technology advanced, they reduced in size to Medium format sensors which are still in use by some camera manufacturers today. This was followed by the age of the Film cameras and finally down to the age of Digital sensors.
Each and every one of these had their advantages and disadvantages which I will not get into in this article. In this post, I will be focusing on digital sensors because these are the most common sensors in DSLRs and mirrorless cameras. It is also very likely that this is probably the type of camera that you own.
Types of Digital Sensors
Sensors have gone through quite an evolution, with the Digital sensor being the latest and most commonly used in cameras today. Before we dive into the world of types of sensors, it is important that we begin with Film. The reason is that digital sensors are built in reference to film used in the 50s, 60s, all the way to the 90s. Film came in different types with different colour profiles. These profiles gave images of different moods and aesthetics.
Film also came with a specific ISO. Yes, if you wanted to shoot in low light, then you had to buy a high ISO film. Even the millennial in me was mind blown.
In a bid to try and enhance the way photographers took images and give them more in a single package, digital sensors were developed. Some of the advantages were, you did not have to constantly buy rolls of film. Secondly, you had ISO control in the sensor itself. You had access to both low and high ISO values and third, you had an unlimited number of images to shoot compared to film where you only had 12 to 36 shots. You finally had the ability to see the image once taken and adjust exposure at that moment. While using film, you only knew your exposure once the film had been developed. It meant there was a need to invest further in a light meter so as to ensure that you always had the right exposure.
I know what you are asking ‘What has this boring history lesson got to do with Digital sensors?’ Digital sensors are built in reference to the size of the film. 35mm film is a term used quite a bit in photography communities and forums. People will say things like ‘what is that focal length in 35mm view?’ You hear stuff like that thrown around as photographers talk. Digital sensors are constructed in reference to the length of the film. The reason being that when digital sensors were first developed camera manufacturers did not want to have photographers have to spend switching to new lenses and systems. So the lens mounts were left intact and a sensor designed in reference to film was created. Based on this premise two types of digital sensors were made.
- Full Frame Sensors
Full frame sensors are digital sensors that are similar in size to 35mm film. Full frame sensors are not exactly 35mm in width they are slightly larger at 36mm. These sensors will be found in Pro-level DSLRs. Read more on theses in this article.
- Crop Sensors
Crop sensor cameras are also referred to as APS-C sensor cameras. These sensors are much smaller than Full-frame sensors and come in a variety of sizes. They are found in Semi-professional and Entry-level camera systems. Read more about these types of cameras in this article.
In the early days of digital sensors, full-frame sensors produced higher quality imagery than their crop sensor counterparts. However, today there is not much of a difference. The major differences between these two systems are usually the field of view and depth of field. Simply put, full-frame sensors tend to produce a much shallower depth than crop sensor cameras but then again there is not such a significant difference when wide aperture lenses are used.
The major difference between these two sensors is the field of view. Crop sensor cameras seem to have a zoomed in effect even when using the same lens as on a full-frame camera. This is the case because of what is called the Crop Factor.
Crop factor simply defined refers to the relationship that exists between the size of a digital sensor in a particular camera to the size of 35mm film. This is very important because this not only defines how much you see (field of view) but also determines the focal lengths of lenses that you invest in. Let me begin by simply explaining the zoomed in effect on crop sensor cameras and how to compute the crop factors.
Crop factor is computed by taking the diagonal of a standard 35mm film sensor and dividing it by the diagonal of the digital sensor of the camera that you own. I own 2 cameras. The Canon 600D and the Sony A7. A quick google search gave me the dimensions of the sensor sizes of these two cameras and I took the liberty of calculating the crop factors of these two cameras as indicated below if you are interested (it’s a ton of math)
From these calculations, we can clearly see that the crop factor for the Sony sensor is x 1.0 The Crop factor for the Canon, however, is x 1.6. What this means is that the Canon’s sensor images will be cropped 1.6 times that of the Sony while the Sony has no crop at all. I want to stop right here and just say that I only took the time to go through the process of calculating all this to demonstrate how crop factor is derived. You will never have to do this to yourself as information on crop factor is already provided by the camera manufacturer. So take it easy (HAHAHA)
In order to have a better understanding of crop factor and how it affects field of view (zoomed in effect) I took my Canon 600D and paired it with a 50mm f/1.8 lens and also paired my Sony A7 with a similar 50mm f/1.8 lens and compared the images that I took of the same subject at the same distance.
Here are the two final images from both cameras side by side.
Looking at these two images, we can clearly see that even though the lenses are of similar focal length, their field of view is very different. This is explained by the different type of sensor built into the cameras. The Sony has a crop factor of x 1.0 as initially calculated, while the Canon 600D has a crop factor of x1.6. This means that the Canon 600D’s images will be zoomed in (cropped in) by 1.6 times that of the Sony. Therefore two photographers shooting with the same lens on two different sensors see two different things. This is very important to understand at the very beginning otherwise you will end up in the group of photographers that believe that only full-frame sensors have the best images. Please do not be that photographer.
Earlier on I mentioned that the type of digital sensor not only affects the field of view that the photographer sees but also affects lens choices. This will mostly apply to those photographers that own cropped sensor cameras. Crop factor produces a zoomed in effect on cropped sensor cameras. This zoomed in effect simply means that you are not shooting at the focal length of the lens that you have mounted to the camera. In this case, you will be shooting at what is called the Effective Focal length. The Effective Focal length is a product of the sensors crop factor and the lens mounted to the camera.
Effective Focal length = Crop Factor X Lens Focal length
Effective Focal length = 1.6 x 50 mm = 80mm
Effective Focal length = 1.0 x 50 mm = 50mm
This example better explains how the zoomed in effect arises. Amongst the many pieces of advice thrown around in the field of photography is that the best lens you can buy is the ‘nifty 50’. There is a good reason for this but this piece of advice is probably not helpful if you own a cropped sensor camera. This is because with a ‘nifty 50’ or 50mm lens you will end up with an effective focal length of 80mm. In layman’s terms, for a cropped sensor camera owner purchasing a 50mm lens, it is similar to purchasing an 80mm lens. You will not have the same field of view as a full-frame camera owner purchasing the same lens of 50mm.
If you already own a cropped sensor camera and have the ‘nifty 50’ because somewhere on the internet someone recommended it or a friend advised that you get one, well my friend you and I got screwed. This is why I want to share this information with you as early as soon as possible. But then again I am sorry but you got screwed (HAHAHA)
The question then is ‘How do I determine the effective focal lengths for the lenses that I actually want?’ Simple take the formula I gave and work backwards.
I want a lens for my 600d that will give me the same field of view that a 35mm lens will give on a full-frame camera.
Actual Focal length = Effective Focal length / Crop Factor (I am sorry there is so much math!! )
So what I want as the final effective focal length is 35mm so to find out the lens I need to by
Actual Focal length = 35mm / 1.6 = 21.87mm
Now if you look through Canons lens choices you will not find a 22mm lens. So what now? You are going to have to compromise a little. Find a lens that gets you to closest to the effective focal length that you want to achieve. In order to achieve a 35mm effective focal length, I purchased the Canon 24mm f/2.8 lens. The effective focal length for that lens is around 38mm. 3mm is not a significant difference and I have never had a client complain that I used the wrong focal lengths. The choice of lenses made will always be based on your creative eye and the look that you want to go for.
The major take away I would like you to have from this article is that you need to understand the impact types of sensors have on your images in terms of field of view and lens choices that you make. I spent about 2 years investing in the wrong lenses because I had not fully grasped this concept, luckily you now probably won’t have to spend as unwisely as I did.
That is all for today’s post, make sure to follow for more comprehensive articles such as these. See you in the next post.