For the same wide-angle framing, is full frame better than APS-C with a wider lens?

Question

I use a Canon 70D (APS-C) and often shoot with a 24-105mm f/4L. On crop sensor, the lens no longer feels very wide because the field of view is similar to about 38-168mm on full frame.

Ignoring price and specific lens quality, what are the theoretical differences between these two ways of getting the same wide shot:
1. using an APS-C camera with a shorter focal length lens, or
2. using a full-frame camera with a longer focal length lens that gives the same framing from the same position?

If the camera position stays the same and the framing is matched, will perspective and field of view be the same? Are there any important reasons to prefer one approach over the other, aside from cost, size/weight, and the optical quality of the particular lenses involved?

user27440 · Accepted Answer

Six of one, half a dozen of the other in terms of FoV. Not so much in terms of expense and the character and size/weight of the individual lenses.

Just me, but if you want your 24-105 to be the wide-angle walkaround it was designed to be, then get a full-frame body to mount it on. When I added a 5DMkII to the arsenal, my usage of the 24-105 changed drastically.

If you just want to shoot ultrawide angle shots without shelling out a lot of cash, then get an EF-S 10-18 lens. If you want a lens that yields similar FoV on crop that the 24-105L does on full frame, possibly grab an EF-S 15-85 IS USM.

Basically, the main issue here is that your 24-105 wasn't designed for crop--it was designed for full frame, and the reason most EF-S walkaround zooms have a 15-18mm focal length on the wide end is to have FoV equivalency with 24-28mm on full frame.

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ADDENDUM: Reformulated answer :)

... Is there any significant theoretical reason for one [to be] better then the other? ... Would the same shot by (1) and (2) have the same perspective? FoV? and/or other properties?

Assuming all the reported number (focal length) etc. are accurate [not always the case with lenses], then the FoV should be identical. The magnification, however, may be different, with different focal lengths, and the DoF will differ, albeit slightly.

The full frame shot will yield a smaller DoF (depth of field), assuming you are only changing focal lengths, and not the vantage point of the camera; or only vantage points and not focal lengths. Changing neither, the DoF would be identical, but the FoV, of course, would not.

Also, inherent lens characteristics, aside from sharpness, such as vignetting, chromatic aberration and distortion are all up for grabs, and depend on the specific individual lenses you're comparing. Crop may have disadvantages in these arenas because of the sharper lens design, but full frame may have a disadvantage because of the larger image circle the lens has to project causing more extreme angles to reach the corners.

For the same wide-angle framing, is full frame better than APS-C with a wider lens?

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