it is said that full frame aperture equivalent of 2.8 to aps-c is 4.2. does it mean that shutter speed of aps-c is one stop slower that full frame on the same aperture? given the same focal length equivalent e.g. aps-c 23mm and ff 35mm.

  • oldlurker114@alien.topBEnglish
    1·
    1 year ago

    A 50mm lens at F2.8 on a crop sensor camera will give you exactly the same depth of field and light as a 50mm lens at F2.8 on a full frame.

    Different light actually. Cropping throws away light.

    And diffent DOF as you enlarge the images from image plane by different amounts to the viewing size, though as the field of views are also diffent, comparing DOFs isn’t IMHO too meaningful.

    So this meant that they would say that a 25mm f2.8 is the equivalent of a full frame 50mm f5.8 – but this only equated to the depth of field and not the light gathering capabilities of the lens.

    The light collecting is a function of several parameters: scene luminance, field of view, exposure time and aperture size.

    We’re only interested in the aperture size here. 50mm/5.6 and 25mm/2.8 both have about 9mm aperture diameter, or area of 63mm^2 or so. Thus the same amount of light goes through.

    The practical implication of this is that the pictures from these systems would look identical to each other.

    If we were to increase the light collecting of either system via making the aperture larger, we’d improve the image quality (noisewise) but also decrease the depth of field.