Crop-Factor Myth – misconstrued misnomers and disseminated confusion.
Photo taken with a D5ll with a full frame sensor, the green line would be what a 1.6 camera sensor would have recorded.
Are we confused yet? Many of us with a foundation from the photography of yesterday seeking an understanding of a new paradigm of digital photography have been unintentionally misled. With the switch from film to the original camera sensors we had to get a new understanding of our equipment both new and old. The first digital camera sensors as well as most sensors today recorded an image on a smaller recording surface than the 35mm film image of yesterday. Our images shot with wide-angle lenses of our film days no longer appeared to be wide-angle images. Our telephoto lens images appear to have more magnification. Yes, this was disconcerting so we attempted to understand. Well meaning camera techno geeks explained in terms intended to simplify concepts but only confused. To make matters worse, in the quest to explain, misleading explanations have misinformed those who have never put a film camera to their eye so incorrect construal of Crop-Factor conception is universal as old hands shared bogus information to those who had never known film.
Photo of Grizzly Bear cub taken with a full frame camera with a 500mm lens, green line would have been the (1.6 crop) if shot with my 7D. The in camera crop gives the illusion of magnification. Regardless of sensor size the 500mm is a 500mm.
Crop-Factor is a term that is used often in the world of digital photography. The terms Crop-Factor and focal length multiplier were coined by techno geeks while attempting to help SLR film photographers who weren’t techno geeks understand how their existing ranges of lenses would perform on newly introduced DSLR cameras that had sensors smaller than the 35mm format, a recipe for misunderstanding, confusion and delusion.
Consequently, many; otherwise, intelligent and knowledgeable people still “believe” in the myth and misnomer of the Focal Length Multiplier, believing the Focal Length Multiplier actually multiplies magnification – it doesn’t! It should be called the Cropping Factor and that is all it is, but Crop-Factor still needs to be understood better. In the techno geeks, honest effort to transpose old variables to a new paradigm technophiles confused instead of clarified.
I am far from being a techno geek, but the idea that my 400mm could be a 650mm didn’t make sense to my rudimentary understanding of physics so I delved deeper, and I found physics still remained constant. My 400mm is still a 400mm.
What does it mean that a camera has a Crop-Factor of 1.6x and how does it affect your focal length? I’ll try to untangle this issue rife with confusion and describe it as clearly as possible. The ‘Focal Length Multiplier’ is the most misunderstood characteristics of DSLR cameras and so lets look at this aspect of DSLR imaging and attempt to lie to rest some of the myths and misunderstanding.
Another example of how the smaller camera sensor crops the photo to give the illusion of magnification
The size of the image sensor is what controls the crop factor, and the sensor is compared to the traditional 35mm film dimensions = 35mm X 24mm; by comparison a 1.6 ratio sensor is only 22.2 mm x 14.8 mm. So when people talk about “Full Frame” camera sensors they are talking about cameras that have a sensor the same size as 35mm film cameras of yesterday.
When you put a 500mm lens on a EOS 7D (1.6 crop factor) you do not get a 811mm lens – it is still a 500mm lens. The focal length; hence, the magnification of a photographic lens is fixed by its optical construction, and does not change with the format of the sensor that is put behind it. It should be noted that the lens casts the same image no matter what camera it is attached to.
When you mount a lens to a camera, it projects a circular image onto the sensor. The lens projects the same size image despite which camera it’s mounted on. When the image hits the film or sensor, a rectangular portion of the round image is registered. A 1.6x sensor has less sensor surface to capture the image than does a full frame sensor therefore less of the projected image is captured on the smaller sensor.
Because of the smaller format of many DSLR sensors, telephoto lenses have a narrower angle area of image registration than the same lens on a full frame sensor. ‘Crop’ is a good term because the imaging area is physically smaller; hence, an auto crop. It is in no way “magnified”. However, the image takes up a larger proportion of the (smaller) frame and so it is easy to see why some people call it a magnifying effect because it is an “in camera” crop that incorrectly alludes to the illusion of magnification. Nothing changes about the lens; it’s simply the amount coverage of the image projects upon the camera sensor.
Lens Crop Factor graphic
The first part of this video I shot with my D5ll wishing I was shooting wit h the 7D, later I swiched to the 7D which made the bears appear closer, not because they were magnified more but because the image was registered on a smaller sensor.
What I don’t hear people speak of is how Crop-Factor manifests itself with wide-angle photography. After buying my first digital camera, a Canon EOS 30D (1.6 crop) I was enthralled with my new ability to stitch photos together to get great wide-angle photos. A few years later I bought a Canon EOS D5ll (full frame) and all the sudden I found I didn’t need to stitch as many photos together as I did with my 30D. I then put two and two together and figured out my new full frame sensor in my D5 ll acted as a de facto, wide angle image recorder. I was thrilled.
I often talk to photographers who buy Canon 7D’s and other smaller sensor cameras when they could afford full frame cameras but choose the cropped sensor models solely for the “Focal Length Multiplier” effect. I cringe when I hear this because they could achieve the same crop in post processing had they purchased the full frame sensor with close to the same resolution. This would also have the benefit of choosing a more suitable crop in post processing. The reason I cringe is because they have short changed themselves of the wide-angle benefit of the full frame sensor and post processing flexibility. Yes it has come to my understanding since publication that some photographers choose smaller sensors for pixel pitch and pixel density but that isn’t the discussion here.
There are a slew of different sensor sizes besides the 1.6 I used for my examples but regardless of sensor size my point remains the same.
Soon after acquiring my D5ll I discovered HD video function and loved it. I have often found when wildlife was out of range for good still photography, it still made compelling video. My video library grew. Post processing video doesn’t allow cropping; I then deduced a smaller sensor could give my video a tighter in camera auto crop. I then bought a 7D for video work for when my subject was too far away. I do switch bodies back and forth as needed for video depending on desired composition or proximity to my subject.
I live in the Greater Yellowstone Region and am lucky to have a plethora of wildlife and embarrassment of riches of landscape right out the door. While cruising for photos I have my landscape gear on my D5ll (full frame) and my telephoto on my 7D. I have to switch them sometimes, but this is the best setup to start a shooting day. Occasionally wildlife will be too close for the registration on the smaller sensor but that usually isn’t the case.