The Leica Q2 camera, released in March 2019, provides several options for “crop-zooming” from its 47Mp sensor and 28mm lens to simulate 35mm, 50mm and 75mm lenses.
My primary use of the Q2 will be for street portraits, and while I have used the previous model Q for these, the extra pixels mean that at 50mm the camera will still produce a file of almost 15Mp.
But one of my concerns was whether the images look like they were shot on a wide lens, giving a wide-lens facial perspective.
However, as explained in my previous post “Is Perspective only a function of distance and not focal length?” perspective is only a function of distance, so this made me think a bit about how I would use the 50mm crop.
When the 50mm crop is selected, guide lines are superimposed on the EVF and on the rear screen, to show the 50mm field of view, so using these means that to fill the frame with a subject’s face, as opposed to the full 28mm fields of view, would mean that the distance from camera to subject would be the same as it would be using an actual 50mm lens, thus giving the same perspective.
I am going to add some examples to illustrate this…
But in the meantime, I can use my approx. lens formula and some simple ratios to work out an approximate difference in distance from camera to subject when filling the 28mm frame and the 50mm frame.
To do the calculation, we need the image size (on the sensor), the object size (the portrait subject’s face), and the lens focal length.
Assuming taking the photo in landscape orientation (so it can easily be cropped square for Instagram!), at 28mm that gives us 5584 pixels height on the full 24mm side of the full frame.
The image size at 50mm crop is 4688 x 3128, so the height of the 50mm crop image on the sensor will be 24 x 3128 / 5584 ≈ 13.4mm.
This could also be calculated using the pixel pitch, which for the Q2 is approx. 4.3 microns (0.0043mm): 3128 x 0.0043 ≈ 13.5mm
So, assuming a fairly tight face crop of 30cm (300mm), the approx. lens formula gives the following distances for filling the 28mm frame and filling the 50mm frame:
d28 = 300 x 28 / 24 = 0.35m (note that the Q2’s closest focus distance is 30cm, so we are just within that!).
d50 = 300 x 50 / 13.4 = 1.12m
In other words, to fill the 50mm frame, the photographer would be about 77cm further away from the subject than when filling the 28mm frame, and thus gets a different and more flattering perspective.