02Jul Crop sensor EF-S lens on a full frame body, Vignetting with the Sigma 30mm f1.4
The labeling of a crop sensor lens can be confusing. The Sigma 30mm f1.4 for example is labeled as a 30mm lens, but since it’s really only designed to work on a crop sensor camera, it has an equivelent focal length of 48mm (1.6 times 30). So why is it labeled as a 30mm lens?
Even though lenses can be designed specifically for a crop sensor camera, the label on the lens still represents what the lens’s focal length would be if it were used on a full frame camera. An EF-S lens can even be used on a full frame camera, although you will end up with strong vignetting as shown in the video.
If you’d like find out more about how the Sigma 30mm f1.4 stacks up against a full frame lens, you might want to check out this earlier post. The 30mm f1.4 is a great crop sensor lens for the price and still sees a lot of use in my lens collection.
July 2nd, 2012 at 8:52 am
Do you have the lens wide open or is it stopped down in the video?
July 2nd, 2012 at 8:53 am
The lens is wide open in this video.
July 3rd, 2012 at 9:58 am
Got this lens for the T2i on your recommendation Deejay, absolutely loving it.
July 3rd, 2012 at 9:14 pm
It’s a great crop sensor lens. Still use mine at least weekly.
August 12th, 2012 at 11:41 pm
I agree that crop sensor lenses have introduced a bit of confusion when it comes to focal length. Why do they still label the aps-c mount lens as 30mm?, it has an effective focal length of 48mm, So what gives? The answer is in the term “focal length”, which is defined as the distance from the rear of the lens to film/sensor plane when focused at infinity. So the focal length of a lens is independent from the size of the sensor, it’s still a 30mm.
A 90mm lens is really long on aps-c, long on full frame, normal view on a medium format, wide on 4×5 view camera, and super wide on an 8×10.
So what is changing when you move a lens from a 5D to 7D, for example, is not the focal length, but the angle of view. It’s just that we are so used to the angle of view that results from a certain focal length/sensor size combo. As someone coming from a still photo background my understanding of a normal lens on a full frame camera is 50mm, but someone coming from the motion picture world is used shooting super35 with a roughly aps sized image would consider a 35mm lens normal.