Confused about EF Lens FOV vs EFS when both are on APSC.

Started 2 months ago | Discussions thread
John Sheehy Forum Pro • Posts: 22,824
Re: Confused about EF Lens FOV vs EFS when both are on APSC.
1

Bionic963 wrote:

I thought I understood that when you mount an EF lens to a 1.62 Apsc crop camera the sensor will not record the same FOV as if you would have had the same mm lens but in EF-S.

The same way that if you take a printed photograph and cut borders off of each edge with scissors; no mojo going on there.

For instance.. If you had a EF 50mm 1.4 mounted to apsc and a EF-S 50mm 1.4 mounted to an apsc.

The only difference is that the EF-S lens assumes that only the central APS-C area of the image circle will be used, so it can optimize that area, and even have a smaller image circle, but may have a larger one anyway. It doesn't matter if the optical design goes bad for areas past the APS-C corners, or if it vignettes out there.

My theory is that the fov of the image recorded on the apsc sensor when using the ef lens will not match. The image recorded when using the EF 50mm lens on an apsc will have similar FOV to what an image recorded with an 81mm EF-S lens on an apsc would have (50mm x 1.62 = 81mm).

No. All EF-S lenses are labelled with actual focal lengths, with the same magnification, just as EF lenses are. In fact, almost all interchangeable-lens cameras use real focal lengths for their lenses. All m43, APS, and FF ILCs use lenses that have the actual focal length. The only difference is that when designed for a smaller sensor, the lens can be designed for optical qualities in a smaller sensor are, and can go black outside of that area, with a smaller image circle.

I thought this was based off the fact that the crop camera has smaller sensor, which results in a narrower field of view equivalent to what you'd get with a longer (1.6 times longer) focal length lens on a full frame camera.

Apparently my understanding of how this works is all wrong. If indeed my understanding is incorrect, then what does it mean when I see members post about liking to use apsc with there zoom lenses because they get "further reach"??

"Reach" is an idea that should go the way of the dodo, IMO (maybe trade it to get the dodo back). Smaller sensors used with the same lenses do not "reach" anything. You are still standing where you're standing, with the same perspective, and the same atmospheric haze between you and the subject, if all you do is use a smaller sensor. The size of the sensor has nothing directly to do with how much pixel resolution you get from a subject with a given lens and distance; that only varies with the pixel density. Any notion that "filling the frame better" as an end in itself has some value, is pure nonsense, when it is because of a smaller frame. Filling the frame better is only directly valuable with the same sensor frame, due to proximity, or more optical magnification (longer focal length). In actuality, the current FF sensors put more pixels-on-subject than the oldest APS-C cameras, by a very big margin, with the same optics and distance.

If the field of view is the same, then how do they get a more zoomed in image simply by putting an EF lens on a crop body?

The FOV isn't the same; the crop sensor limits it to a narrower one, and that in and of itself has no IQ benefit at all; it is a pure limitation. Only higher pixel density is beneficial, which sometimes happens with smaller sensors, but not always.

I shoot with an APSC body. I have the EF-S 17-55mm, and the EF 50mm. Tommorw I plan on mounting the 50mm EF lens and take a photo, then I will mount my EF-s 17-55 and zoom to 50mm on the apsc and take a photo, them compare them.

I already know the answer. 50mm means the same magnification for both EF and EF-S lenses.

Interested to finally get a good understanding of this.

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