The crop has a shorter depth of field and, of course, a far more detailed picture at full aperture compared to a 40 f/2.8 STM. Live view also has a lengthy focusing time. When compared to an aperture of 85 f/1.8, let alone XA, its visibility is essentially nonexistent. There are situations where a 50mm crop is preferable to an 85mm one. For one thing, a shutter speed of 1/80 s is sufficient to avoid blurring, while a speed of 1/160 s is required for an 85mm lens. Both the 50mm and the 85mm have almost the same depth of field.
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