Today’s Question: If I stand in the same location, center the same subject, and use the same lens, what changes if I use a Full Frame camera body (with a larger sensor) instead of an APS-C camera body? I want to know what (if any) the lens prospective variations (and Lightroom [Classic] corrections) would be between different camera bodies with different sensor sizes. Or are these corrections dependent only upon the specific lens used?
Tim’s Quick Answer: With the same lens from the same position, using a camera with a full-frame sensor (35mm equivalent) versus a “cropped” sensor (such as APS-C), the only difference would be the cropping of the image circle projected by the lens. If you apply profile-based lens corrections in Lightroom Classic, that correction will take into account the sensor size, to ensure the correction is applied correctly across the frame.
More Detail: Each lens has its own unique behavior, which tends to be most significant with wide-angle lenses. Those behaviors often relate to distortion of the scene and vignetting of the edges of the frame. Many software applications, including Lightroom Classic, enable you to apply automatic corrections to a photo based on the lens that was used. These are generally referred to as profile-based lens corrections.
These corrections will take into account the sensor size of the camera used in conjunction with the lens, so the correction can be applied correctly. For example, a smaller sensor means the image circle projected by the lens is being cropped more than would be the case with a full-frame camera. Therefore, the vignetting that is part of the lens behavior would also be at least partially cropped out of the final photo. The profile-based lens correction therefore needs to apply less vignette correction (in terms of total area) for a photo captured with a cropped sensor (such as APS-C) as compared to a full-frame capture.
The perspective of the scene will not be affected by the cropping of the image circle, assuming the camera position is the same. Only the image circle projected by the lens is cropped to a smaller size, while the projection of the lens remains the same. Thus, you would get the same photo if you captured a scene with the same lens on a cropped versus full-frame sensor, and then cropped the full-frame capture to the same cropping as the camera with the smaller sensor. Furthermore, the profile-based lens corrections will compensate for the differences between the captures with the two different sensor sizes.