Short Description

Crop factor applies only to 35mm SLRs, other camera segments may have crop factors but their lenses are rated as 35mm equivalents. The crop factor applies to SLRs who's sensors are smaller than a full frame 35mm sensor(36x24mm) but still use 35mm lenses. The crop factor illustrates how much larger a 35mm film is versus the smaller sensor along a single dimension. The ratio is also known as the focal length multiplier which illustrates the relationship between focal lengths of a lens when used with different sensor sizes.

For instance a 35mm sensor diagonal is 1.5X bigger than an APS-C sensor diagonal (the most common dSLR sensor) - thus its focal length multiplier is also 1.5X. Because the sensor is smaller than a full frame sensor the lens projects more image than the sensor can cover - hence the projected image is cropped and thus the name - crop factor. The focal length multiplier allows you to figure out how much is cropped by providing the equivalent focal length of magnification. For instance an image taken on a APS-C camera at 50mm will look like the same image taken on a full frame camera at 75mm - 1.5X magnification. This means smaller sensor SLRs get built-in zoom with a given lens relative to a full frame camera but they also loose the ability to go as wide angle as the full frame camera.

Visualization of Crop Factor

The following diagram shows the image projected by a lens and the relative differences between how much a full frame sensor is capturing and how much an APS-C frame captures. As you can see the smaller sensor captures less, but if it has the same number of pixels than on a relative basis the effect that is caused is basically zoom. If the full frame sensor was to capture the exact same image as the APS-C sensor you can see that the projected image would need to grow - in fact it would need to grow by exactly 1.5X - the same as the crop factor.

Illustration of Crop Factor on a Full Frame vs APS-C
illustration of a projected image being captured by full frame vs aps-cThe photo illustrates the difference between what a standard 35mm full frame sensor captures and a smaller APS-C sensor. It also illustrates the relative zoom afforded by the APS-C sensor and the wider angle afforded by the full frame sensor.

Top Full Frame Cameras

The following SLRs are some of the best full frame digital 35mm cameras available.

Nikon D610
Nikon D610
from $1,797
Low light performance Low noise at high ISO Help
2,980 ISO
Overall image quality Great image quality Help
94.0
Screen size Large screen Help
3.2"

Learn more about the Nikon D610

Nikon D750
Nikon D750
from $2,297
Low light performance Low noise at high ISO Help
2,956 ISO
Overall image quality Great image quality Help
93.0
Screen resolution High resolution screen Help
1,229k dots

Learn more about the Nikon D750

Nikon D4s
Nikon D4s
from $6,497
Low light performance Low noise at high ISO Help
3,074 ISO
Battery life Great battery life Help
3020 shots
Overall image quality Great image quality Help
89.0

Learn more about the Nikon D4s

Nikon DF
Nikon DF
from $1,494
Low light performance Low noise at high ISO Help
3,279 ISO
Overall image quality Great image quality Help
89.0
Screen size Large screen Help
3.2"

Learn more about the Nikon DF

Green arrow See more of the top DSLRs with full-frame sensors

Top APS-C Cameras

The following APS-C cameras are some of the best available.

Pentax K-3
Pentax K-3
from $842
Low light performance Low noise at high ISO Help
1,216 ISO
Cross type focus points Many cross-type focus points Help
25
Screen size Large screen Help
3.2"

Learn more about the Pentax K-3

Nikon D7100
Nikon D7100
from $1,047
Low light performance Low noise at high ISO Help
1,256 ISO
Movie format Full HD Help
1080p @ 60fps
Overall image quality Great image quality Help
83.0

Learn more about the Nikon D7100

Nikon D5300
Nikon D5300
from $650
Low light performance Low noise at high ISO Help
1,338 ISO
Movie format Full HD Help
1080p @ 60fps
Overall image quality Great image quality Help
83.0

Learn more about the Nikon D5300

Pentax K-50
Pentax K-50
from $397
Light sensitivity High ISO Help
51,600 ISO
Weather sealed Weather sealed Help
Shoot in extreme weather
Image stabilization Image stabilization Help
Sensor shift

Learn more about the Pentax K-50

Green arrow See more of the top DSLRs with APS-C or APS-H sensors

Discussion

Showing 3 comments

Johnsmith (7:34 AM, April 05, 2012)
Canon APS-C have a 1.6x crop factor (smaller sensor) so your 18mm = 28.8mm 
 
Roy Amrullah (9:16 PM, September 09, 2011)
550d seems to have 1.5x cropfactor then 18mm x 1.5 = 27mm. CMIIW
 
Avatar for Justin Ji Justin Ji (4:32 AM, June 15, 2011)
Nice! I was wondering why a 18mm lens on a 550d (APS-C) had less wide angle ability than a 26mm equivalent Nikon P100! : )