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Which sensor "full frame" vs. APS-C (1.6 crop) gives more distortion using the same lens? I mean, would a 10mm lens on a full frame camera show more or less distortion than if it were on an APS-C (1.6 crop factor) sensor camera?

You see, I have a Canon T3i (APS-C) and would like to time lapse the milkyway with out a lot of barrel or linear distortion. I've been looking to get the Rokinon 14mm lens but found that it only has 81.2° of angle (FOV). I'd like a wider lens with a larger angle (FOV) to accept as much of the milkyway in the FOV for as long as possible, but without too much distortion.

  • On a FF camera the AoV for that lens is 114º. – Michael C May 24 '15 at 18:53
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The full frame camera will generally give more distortion than a crop body camera with the same wide angle lens because the wider angle of view obtained with a FF camera includes the edges that are cropped when using the same lens with an APS-C camera. Cropping the FF camera's image to get the same Field of View (FoV) as the APS-C camera will yield the same amount of distortion with the same lens. The Rokinon (Samyang/Bower/etc.) you asked about has a 114º diagonal FoV when used in a FF camera, compared to about 71º on an Canon APS-C camera. That lens has an unusual distortion pattern with a pronounced bulge just inside the area used by an APS-C camera.

Since distortion is a characteristic of each individual lens design, it is hard to say whether a 10mm lens on an APS-C camera will give more or less distortion than a 14-16mm lens on a FF camera. In this comparison between the EF-S 10-18mm f/4.5-5.6 and the Samyang (Rokinon/Bower/etc.) 14mm f/2.8 the 10mm on APS-C demonstrates considerably less distortion than the 14mm on a FF camera. Of course you sacrifice between one and two stops of aperture as well. The Canon EF 14mm f/2.8, on the other hand, has less distortion at 14mm on a FF body than the EF-S 10-18mm f/4.5-5.6 and the EF-S 10-22mm f/3.4-4.5 do at 10mm on an APS-C body.

  • Thank you for sharing. It seems the cropped area of the FOV on a FF camera sensor, w/ any particular lens, "is", the FOV the APS-C sensor displays. The distortion or perception will be identical for that area of both sensors. So, if there is little or no distortion in the FOV w/ a 16mm lens on a FF camera, then I could use a 10mm lens on my APS-C sensor, get the same low distortion and a wider angle. – Steph May 25 '15 at 12:00
  • Maybe, but each lens is its own design. Just as the 14mm Rikinon/Bower/etc. has a LOT more distortion than the 14mm Canon when used on the same camera, so one 10mm APS-C lens may have more distortion than another on your APS-C camera. One 10mm lens might be less distorted on an APS-C camera than a particular 16mmm lens on a FF camera, the other may be more distorted. – Michael C May 27 '15 at 2:12
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I think this is an "apples and oranges" comparison - of you use the same lens on a full frame and a crop camera, you get different fields of view, so it's not really meaningful to compare which has more distortion.

That said, the literal answer to your question is using the lens on a full frame camera, as you're then using the full extent of the lens's imaging circle, and it's always the outsides of the circle which have the greatest distortion. But... if you cropped the image from the full frame camera to give the same FoV as from the crop camera, they'd have virtually identical distortion characteristics.

  • Thank you for sharing. It seems the cropped area of the FOV on a FF camera sensor, w/ any particular lens, "is", the FOV the APS-C sensor displays. The distortion or perception will be identical for that area of both sensors. So, if there is little or no distortion in the FOV w/ a 16mm lens on a FF camera, then I could use a 10mm lens on my APS-C sensor, get the same low distortion and a wider angle. – Steph May 25 '15 at 11:59
  • No, because you've changed lens. Your 10mm lens may (almost certainly will) have significantly worse distortion characteristics than your 16mm lens. – Philip Kendall May 25 '15 at 12:08
  • If the distortion is more on the edges, then you shouldn't see most of it on the cropped area of a 10mm lens that the APS-C sensor pics up. I mean, if there is little distortion w/ a 16mm lens on a FF camera, then there is less on the cropped portion an APS-C sensor would pick up. I would think then, to get the same low distortion of the FF camera sensor w/ a 16mm lens, I could use a wider angle lens w/ the 1.6 sensor? Maybe not? I feel like I'm not getting it now. Sorry for the confusion and waste of time. – Steph May 25 '15 at 12:17
  • The 10mm lens is almost certainly designed for APS-C use only, so the edges of the smaller image circle are included on your APS-C sensor. One reason APS-C only lenses are cheaper is that the smaller light circle means less correction is needed than would be the case with a larger image circle. – Michael C May 27 '15 at 2:15
  • If a 10mm APS-C lens were made to cast a light circle large enough for a FF camera but only used the correction in the original APS-C lens, the distortion on the edges outside of the APS-C sensor area would be horrendous. Far worse than one designed to cast a FF size image circle and corrected by the designers to do so. – Michael C May 27 '15 at 2:17

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