Re: Canon EF 135mm f/2 L vs 85mm 1.2L for portraits?
jedibrain wrote:
This is not correct. The image circle created by the lens does not change, including its DOF, with the size of the sensor or in camera crop. You could hold that lens up with no body at all and it Will project an image on to a piece of paper. The scale and DOF of that image will not change when you change the size of the piece of paper. All the camera is doing is cropping the full image for you - the DOF would not change if you cropped a full frame image to APSc sized in post.
The idea that DOF changes with crop factor is only true if you correct your focal length to get the same FOV as you would have gotten on 35mm/FF. So you use an 85 instead of a 135, and get a wider DOF because of that (DOF is wider at a given aperture as you make your focal length shorter). But that 85mm lens always makes the same image size and DOF no matter what body it is attached to. It is not the camera, sensor size, or in camera cropping that changes the DOF.
Brian
Jesse Evans wrote: jedibrain wrote:
According to a DOF calculator, at 10ft max aperture, the dof of the 85 at 1.2 is .3ft. And the 135 at f2 is .2ft.
The OOF areas are not just a function of DOF though. I don't have both, but the 135 is pretty darned good. I hardly use my 85 1.8 anymore, but it is not as good as your L series.
Have you considered renting one to try? Or if you buy used and don't like it, you'll probably be out less than a rental fee to resell it.
Brian
One thing to keep in mind is that if you use a Canon crop mode on the 85/1.2 it will yield equivalent dof of a 136mm f/1.92 lens.
I’m not sure I get your point.
Depth of field calculations require a circle of confusion variable as input.
If your circle of confusion was 10 micrometers at 85mm in full frame during computation, to find the depth of field when cropped to 135mm you would divide the circle of confusion by 1.6. This is because by cropping you will magnify the image, thus the blurred pixels become apparent at a smaller CoC.
If you use the tool above you can see these numbers play out. At 85/1.2 with a CoC of 0.01mm (10 micrometers) and a subject distance of 10 feet, there will be 0.1ft of DoF.
Reducing the CoC to 0.006 (0.01/1.6) to accommodate for a 1.6x crop factor, results in a DoF of 0.06 ft. Which happens to be the exact same amount of DoF for a 135/2 at 10 feet with a 0.01mm CoC.
The physical properties of the lens will never change, you are correct. If you assume a same viewing magnification for a scene (e.g. cropping to match) between any 2 focal lengths the only indicator of which has the shallower depth of field is the size of the physical aperture. Since the the 85/1.2 has the larger aperture, it will have the shallower DoF even if it is a rounding error.
All of this is to say that you should not expect to achieve shallower depth of field with the 135 f/2L over the 85 f/1.2L cropped to 135mm.
Oct 27, 2021 at 10:43 AM
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