In this tutorial I’m going to be explaining the differences between different sensor sizes, what are the distinctions between the various lens mounts and manufacturer, what a crop factor means and what are the benefits of getting a full frame camera compared to APS-C or micro 4/3rds. It is part of a set of tutorials I have been making on the basics of photography, the previous ones I covered the basics of camera operation and the differences between different types of lenses and this video is going to build upon the concepts that covered in those. Fundamentally the key concept I’m going to be covering is different camera sensor sizes and how they interact with lenses. It is a rather simple concept with major implications for when you are choosing what type of lens to purchase and the operation of your camera.

Sensor Size:

So, I’ll get started with sensor size, there are 3 most common sensor sizes, Micro 4/3rds, APS-c and full frame. these are not the only options on the market as there are medium format cameras, 1-inch sensors and even technically the small sensors found inside phones these days, but to keep things simple I’m just going to be talking about the more common options for DSLRs and mirrorless cameras.

Full frame cameras have been the most popular option for professionals for many years now, mainly because it is the same size as traditional 35mm film cameras and the inherited the benefits of a larger surface to capture light on and can utilize the same lenses. However since digital cameras became absolutely dominant a couple decades ago Micro 4/3 and APS-c sensor cameras are far more popular for casual photographers because of the more affordable price and smaller camera size. In recent years even as digitals sensors have gotten better and better and lens manufacturing has improved so dramatically as well, the size of a sensor is much less relevant to the quality of the image than it used to be.

Choosing Between Sensors:

The natural next question is which sensor size is best and unfortunately there is no clear cut answer to this question as it’s a rather complex topic. The easiest answer is the best sensor for you is going to be the one in the camera that you have, the real answer is it completely depends on what you’re using the camera for, and there is no real best option for everyone.

Larger sensors can capture more light, allowing for better potential lowlight performance and higher resolutions but at a substantially larger size, weight and cost. Smaller sensors conversely have the inherent benefit of being compact while also offering more compelling features because of their more efficient design allowing often better video features as well as compelling computational options that larger sensors just can’t utilize yet. There are also other benefits to having larger sensors such as having different character to the out of focus areas because of the way larger lenses interact with the sensor and some disadvantages with rolling shutter on some larger sensors because of their size. Really what it comes down to though is often your budget and thankfully these days there are lot of options on the market and most of them are all fantastic.

Crop Factor:

In a previous video I discussed how lenses are categorized based on how many millimeters they are like 16, 50 or 200mm, and the overall concept of wide-angle, mid range and telephoto lenses. However, I mentioned that it’s hard to categorize lenses by how many millimeters they are because a lens is going to behave differently depending on the sensor size of the camera you’re using it on.

Most commonly camera lenses are talked about with respects to how they work on a full frame camera, and people will refer to Micro 4/3rds and APS-c cameras as ‘crop’ sensor cameras, because of how they ‘crop’ in on an image. An APS-c camera will be cropped in x1.5 or x1.6 times on an image depending on the brand, so say if I am shooting on a full frame camera with a 50mm lens, if I use that same lens on and APS-C sensor it will look like a 75mm full frame lens. This results in APS-c lenses being slightly zoomed in when compared to the same focal length on full frame cameras. If you compare Micro 4/3rds sensor camera lenses to full frame it is a 2x crop, so 2 times more zoomed in on an image. For example, a 50mm lens on a Micro 4/3rds sensor camera is visually equivalent to a 100mm lens on full frame.

Often if you are in conversation with some one talking about a lens you will hear them say ‘the full frame equivalent’, which is referring to how the focal length appears on a full frame camera. It is a confusing topic though, and it is ok not to 100% grasp it because it’s really hard to understand the difference between lenses if you don’t work with different focal lengths often. A lot of the information will make more sense with time as you practice more with your photography and getting more comfortable with using the lenses that you have. The key concept of all of this is that different lenses will capture different images depending on the sensor size that they are used on and the best way to figure out how ti works is to try it out so see it in person if you can.

Lens Mounts:

Next up is another relatively complex topic, and that is lens mounts. On the back of every lens and the front of every camera is a lens mount, its how they attach themselves together. Some camera manufactures share mounts and some brands do not, for example, a Canon RF mount lens wont mount to a Sony EF camera. This is because they are fundamentally designed differently, it is like putting the wrong key in a lock, they just don’t work together. This is particularly important for mirrorless cameras because most camera manufacturers took the opportunity to design new mounts for their cameras when they made their mirrorless cameras. So, an old Canon EF lens will not mount to a new Canon RF camera and even though they are the same brand they require different mounts and you will need an adapter to use an EF lens on an RF camera.

Besides being relevant to the camera brand, what mount a lens has is often related to the sensor size as well, so a lenses designed for a sony APS-c camera like the a6000 would be a Sony E mount lens, where as a lens designed for a full frame sony camera like the a7iii would be a Sony EF mount lens. It gets more confusing because all Sony E mount lenses can physically attach to Sony EF cameras, but they do not actually cover the sensor of the full frame camera sensor. This is because in order to capture enough light lenses need to be larger for full frame sensors and for smaller sensors like micro 4/3rds and APS-C cameras, the lenses are able to be smaller as they need less light to cover the sensor.

The last thing to keep in mind with lens mounts is 3rd party manufactures like Samyang, Zeiss, Tamron and Sigma all often make the same lens for multiple camera mounts, for instance, the lens I always recommend for new photographers is the fantastic Sigma 30mm f1.4, which is a crop sensor lens that has multiple versions of it made for Sony E, Canon EF-M and Micro-3/4rds mount cameras, so be mindful that even though the lens might be the exact same, the mount on the back of it needs to be different depending on the camera that you have.


The last idea that I’m going to talk about is going to be adapting lenses to different camera mounts. Not all camera mounts can be adapted to each other. Typically the most common way to adapt lenses is to take older lenses and adapt them to new mirrorless cameras because the flange distance is often significantly smaller on mirrorless cameras allowing them to be compatible with lenses designed for DSLR. Adapters also can have the advantage of containing things such as variable ND filters or speed boosters which are concepts I hope to cover in other videos are very compelling options for video shooters. Fundamentally when you’re getting started my recommendation is you do not use adapters and even once you are more experienced it is often more advantageous to buy native lenses than to adapt old lenses to new cameras as the act of adapting a lens will almost always reduce some functionality of a lens with relation to its autofocus capability, weather sealing or handling.


So now that we have the idea of sensor sizes and camera mounts under our belt it’s time to actually put it all together. The key thing to keep in mind while you’re looking out for a new lens is first of all what is the camera you are using and the mount and sensor size that your camera has. With that in mind you can consider what type of lens you’re looking for whether it be a zoom lens or prime lens and what type of photography are looking into cover the focal length that will be best for that whether it be a wide-angle lens or a telephoto lens which I discussed in my previous tutorial. Choosing a new lens can be a very stressful thing and the fear of making a mistake or wasting money is often a very real concern, however if you take your time and do your research I’m sure you’ll come out with a fantastic decision.

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