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| p.4 #9 · 1.2 and 1.4 wasted on 35mm and 24mm? |
I think there is a flaw in your understanding of the effect of aperture on background blur at different focal lengths. This is a bit tricky to explain in text, but I'll give it a try.
f/1.4 is, indeed, f/1.4. But the effect of f/1.4 is not the same when the focal length varies.
Imagine that you are shooting some subject and you want this primary subject to fill half the width of the frame, leaving the rest of the frame for out of focus back ground elements. Obviously, using a wide lens (let's say 24mm) you'll have to move much closer to your subject than if you use a long lens (let's say 100mm) if you want the primary subject size to remain the same.
But when you do this, the background is going to be a lot different in the two frames. A much larger area of background will be included in the 24mm shot, and a result is that not only do objects in this background area appear to be much smaller, but the OOF aspect of the background also appears much smaller. With the longer lens you are essentially "looking more closely at the OOF background," and the smaller background area in the frame will seem more out of focus.
(This is why using a long lens will generate a more OOF background and why we say that a wide has greater DOF.)
Sorry I don't have the time or inclination to knock together the example images that would show this. I'm hopeful that if you think about the text description you might make sense of it. Alternatively, you could simply try the experiment - use two different focal lengths at the same aperture; move the camera position so that the primary subject fills the same portion of the frame with both; then compare what you see in the background areas of the image.
Ok, I agree that "enough" background blur may require close enough focusing with the 35mm... but it is the aperture what matters for a given distance, so F1.4 is F1.4 (even in wide angle) and the same effect can not be achieved with slower lenses (except by going even more close, which is not the same shot). The focal length only changes the working distance and the perspective, never the DOF... thus a wide blurred background requires a wide angle fast lens, which is full of sense.
I think that every lens has its own place and reason:
35mm F1.4: relatively heavy,...Show more →