I see a LOT of discussion around the subject of full frame versus cropped bodies. Especially the people coming from the 35mm film world that have moved to digital full frame seem to have trouble grasping the concept and implications of using a cropped sensor. In this blog post I’ll try to explain what is what, where you would use what solution, and the differences between the EF and the EF-S mount.
A bit of history: When 35mm film became digital
I am not going to explain the entire down-to-the-detail history of the digital camera here. I’ll do the “short-short” personal-interpretation version violating orders of events and details as I see fit 🙂 :
At one point in time there was analog film for cameras to use. Then the “digital revolution” took place, and people at camera making companies started to wonder if they could replace the analog film with a digital sensor. As we can see today, you can. But looking at the 35mm analog film cameras, that would be both hard and expensive to build: You’d need a sensor the same size of a 35mm analog film frame, which from a chip’s perspective, is HUGE in size.
So the camera makers decided on making a sensor that was actually smaller than the 35mm frame format, and would be sitting in the center of the original full frame area inside a camera very comparable to the 35mm analog film camera: The cropped sensor was born. The name “cropped” is actually a very accurate one, as you literally crop the image projected on the original sensor full frame sensor down a just the center portion of the full frame sensor. The result? A cheaper sensor, and a field of view that is narrowed down by the crop.
Now let us put the focus on Canon. They choose a factor 1.6 to crop their sensor down to, and called it APS-C (or more popular: cropped). In the 1D series also a factor of 1.3x (APS-H) is used, but I will not focus on this in this blog post, as most readers will probably be using one of the APS-C cropped bodies or full frame bodies.
Now that Canon had this camera with the smaller, cropped sensor, they figured you could build cheaper lenses as well. These lenses would only have to project the image on a smaller portion of the original 35mm frame. Another bonus was, that the mirrors in the cropped DSLRs are smaller, thus leave more room for the lens inside the camera. Lenses made specifically for digital could actually have a protruding rear element that sat inside the body. This simplified lens design even further, and made the “digital lenses” even cheaper.
One big issue though: when you’d put one of these “digital only” lenses on a full frame camera, the mirror would crash into the protruding rear element of the lens, plus that a full frame camera would see a circular vignette instead of a full image. For exactly this reason , Canon invented the EF-S mount. This mount is used by “digital only” lenses. Any cropped body could take both EF (“full frame lenses”) and EF-S lenses (“digital only lenses”). Full frame bodies can physically only take EF lenses to avoid damage to the mirror and the vignetting issue.
You can always quickly tell the difference: The EF-S lenses use a white marker to mount them, while EF lenses use a red marker:
Funny detail: When you look at the very old Canon D30, you’ll notice it only features a red marker, so it takes EF lenses only. Still, it features a cropped (1.6x) sensor. This is an example of one of those camera’s “historically in between” the cropped sensor and the EF-S lens:
Focal length = Focal length
Some people tend to think there is some magic going on between the EF and EF-S lenses when looking at their focal lengths. Fact of the matter is, there is no magic whatsoever. Focal length is focal length. Both cropped and full-frame camera use the same sensor-to-flange distance (also called flange focal distance). You could say that the EF-S mount is backwards compatible with the EF mount.
That said, there should not be any difference if you moved a 50mm lens between full frame and cropped, right? Wrong…
Focal length does not change the world… But sensor size does!
So we have seen that focal length is just focal length. But as the sensor size differs between cropped and full frame, so will the viewing angle. So if you are thinking about changing from cropped to full frame or the other way around, you need to consider two important things about your lenses:
- Will they physically fit (if you have EF-S lenses they will not fit on full frame);
- Will the focal lengths of my lenses still “work for me” on the other sensor size.
The first one is an easy one: When you go from full frame to cropped, you can still use your (EF) lenses. When you go from cropped to full frame, you must consider your EF-S lenses as being unusable on the full frame body.
The second one is a more complex one: As you move between cropped and full frame, your lenses will all of a sudden see the world in a different angle. Your cherished 400mm lens on cropped will appear to you as a (400mm /1.6) = 250mm on a full frame camera. You beloved 24mm f/1.4 lens on full frame will be nice and wide. But when you use it on a cropped body it will appear to you as a (24*1.6) = 38.4mm lens, not so wide anymore.
As you can see, it is just what you’re used to. Some people will say “focal length is focal length”. Although that in itself is a very true statement, the changing of the sensor size will make you perceive your lenses to be different (even though they’re not).
Some real life examples
Time for some cool examples. For each example, remember that the camera type I start out with is the camera type (cropped or full frame) you would have been used to before you swap between the types.
Example one: 400mm lens on full frame
You have a full frame camera, and a 400mm lens. You are not really happy with the reach of the lens, but you are scared away by the immense pricetags of 500+ mm lenses. Now you try your 400mm on a friends camera that has a cropped sensor: WOW! Your 400mm now appears to you as a 400*1.6 = 640mm lens!
Example two: 400mm lens on cropped
You have a cropped camera, and a 400mm lens. You are happy with the reach, but you want to increase the image quality, so you buy a full frame camera. Your 400mm lens will now appear to you as a 400/1.6 = 250mm lens, and the reach really disappoints you. In order to have the same reach on full frame, you’d actually need to upgrade to a very expensive 640mm lens.
See where I’m going with this? It is not about the numbers on the lens, it is about how you perceive a lens though YOUR camera. Changing the camera really changes the way you can use your lenses, as I’ll show in the next examples:
Example three: Shooting head and shoulder portraits on cropped
You are happily shooting portraits with your 50mm f/1.4 lens on a cropped body. As you want to increase the image quality, you upgrade to a full frame camera. Next thing you know, people are unhappy with the pictures you take; they claim their noses appear to be “blown up” on the pictures. So what happened? As you took your 50mm lens from cropped to full frame, the viewing angle got wider. So for that same portrait composition, you now need to get much closer to the subject. Result: perspective changed which gives you unflattering results. How to fix this? When taking portraits, the distance to the subject is vital (also see “A perspective on “flatteringness” of portraits“). Changing distance will change the perspective, which you do not want. Solution: for the same perspective on full frame you need the same working distance. If you were to buy a 50*1.6 = 80mm lens (so you’d probably end up with a 85mm lens), you’d end up with the same working distance and the same perspective.
Example four: Shooting weddings on full frame
You are shooting weddings on full frame using a 24-105L lens. This lens is considered to be THE wedding lens by many people, and you focal reach is excellent on full frame. You have a backup body that is a cropped camera. You consider buying a second 24-105L lens for this cropped body, but you discover the focal reach of the 24-105 does not seem to work for you on this body at all; the view is too narrow, and you need bigger rooms to get your shots! This of course makes sense; as you are used to full frame, the 24-105 on a cropped body will appear to you as a (24*1.6) to (105*1.6) = 38-168mm lens on the cropped body! How to solve this? For cropped, you’d need to get a (24/1.6) to (105/1.6) = 15-65mm lens for your cropped camera to perceive the same reach on cropped. So you’d probably end up getting a 15-85mm EF-S lens.
The conclusion is really simple: No matter what numbers you find on a lens, it is how you perceive that lens on the body you are used to (cropped or full frame). Whenever you move between types of bodies, the perceived focal range of your lens will change (even though the lenses itself will obviously not). So changing between cropped and full frame can have impact on the lenses you have; even though they might work technically, they might not work for you for the purpose you initially bought them!