I only own only one f/1.4 lens (50mm f/1.4G) which I use in combination with a D7000. I have a question about how the aperture affects the bokeh compared to f/1.8.
If I take a shot at f/1.4 of f/1.8 with this lens, the out of focus background blur looks identical. I cannot tell any difference in blur at all, whereas if I set it to f/2.8 the difference is quite noticeable. Literally, the blur looks identical to me at f/1.4 and f/1.8. Is this normal? Would this also be the case at other focal lengths (24mm, 35mm, 85mm)?
The blur would look similar to a point. This is Normal, the more you stop down, the more dof you will get. this is the same with all focal lengths. faster lenses will always get you a shallower dof, but in some cases it might be hard to tell apart a 1.4 lens and a f2 lens.
But 'blur' isnt the only reason to get a fast lens. the 1.4 is 2/3 of a stop faster, so if you shoot 1.4 / 1/100 / iso100, then if you had to use f1.8, then your shutter would drop to 1/60 at the same iso. a big difference, especially if you have to hand hold. faster lenses will make it easier to get photos without camera shake in low light.
Lenses typically perform better stopped down a bit, so you may see an f1.4 lens performing better at 1.8 than would the 1.8 version at 1.8
Or try an 85mm 1.4 set at 2.8 vs. a 70-200 2.8 zoom set at 85mm and f2.8
Your example is a subtle difference, yes, but it's not all about the degree of blur, it's often the overall way a lens 'draws' a photo - take a bunch of different 50mm primes, all shot at f1.8 - they will all take the same photo in their own distinct way -
Yes, the difference in background blur is fairly negligible (depending on focal length also) between 1.4 and 1.8. The biggest difference in those two apertures for natural/low light shooters is that 1.4 gives nearly twice the shutter speed as 1.8. This can mean the difference in getting the shot if photographing dancing by candlelight or something similar..
I understand. So is it because of the circular shape of the iris, that 1.4 and 1.8 makes a small difference in the width/height of the iris circle (and thus blur), but a large difference in the surface and thus entering light?
I was wondering if other factors came into play that resulted in f/1.8 and f/1.4 looking so similar.
I could only test this for a 50mm lens... Would it be similar on a 24mm or an 85mm lens? That the difference in blur is negligible?
