Canon 50mm f/1.8 STM Focus/DoF issues

On Saturday I had the chance to try out a 50mm f/1.8 STM lens.

So I set up a quick test to compare sharpness, focusing, bokeh etc.

I compared the 50mm to the 24-70 2.8 L (Mk1).
But the results were much more interesting I ever tought.

This was my setup, 2 lenses, one closet, the other a little bit away.

I focused on the "Zoom Lens EF 16-35mm 1:2.8 L USM" text on the 16-35, and on the AF/MF, IS On/Off, etc, buttons on the 70-200.

First the close focusing.

The 50mm was very sharp at f/1.8, and even sharper at 2.8, this was the result I expected.
Even sharper then the 24-70.

Then I compared it to the 24-70, and I was really suprised...

Even at f/1.8 the DoF of the 50mm was much larger then that of the 24-70 at f/2.8.
Can someone explain this?

50mm @1.8:

Next, the focusing on the 70-200.


The 50mm could be sharper here, too, yet it missed 3 out of 5 times the focus.:

See:
50mm @1.8

Continued:

50mm @2.8:

not sure about the DOF of 1.8 seeming larger then the 2.8
but looks like your lens was acting like mine was..Would just totally miss focus like 40% of the time even on well lit static subjects. I ended up returning mine because of that
Wait for all the posters to come in and say what do you want its only $125
I dont care if its $50 I want it to atleast be able to focus on a static subject in daylight consistently. We all know if this was a Sigma people would be mobbing up to say how awful sigma is but since its Canon most will say thats ok I will accept a poor performing lens because its made by canon

Thanks for these real life examples.

ok was thinking..maybe your 24-70 has a slight front focus issue to it causing the focal plane to shift forward a tiny bit. maybe it needs a little bit of MA to it to fix the issue?
Oh and you will also get some posters claiming you dont know what your doing cause the 50mm missed focus.

My 24-70 is spot on focused properly on the places I focused it. "16-35" text, and the switches on the side of the 70-200,
they are sharp in all pictures.
So why do you think, it has a front focusing issue?!
I am curious, as you might be right, I never checked, but usually its properly sharp.

just was a guess. I mean you could have proper focus on what you focused on but there may just be a very slight focus shift forward but still what you are focusing on is falling in the DOF area giving proper focus on what you are shooitng. but since it might be moved forward its making it look like the 1.8 has more DOF

i have a feeling i read somewhere this:

If you use f2.8 as a fixed fstop, if you take a shot at 24mm the DOF will be deeper than if you shoot with the same lens at 200mm. so the more zoom, the shallower the DOF?

Im happy i switched to sony, those look all soft IMO

urbanfreestyle wrote in post #17606428
i have a feeling i read somewhere this:

If you use f2.8 as a fixed fstop, if you take a shot at 24mm the DOF will be deeper than if you shoot with the same lens at 200mm. so the more zoom, the shallower the DOF?

both shots are taken at 50mm

All shots were taken at 50mm (Well 51 with the 24-70, but that should not matter)

05Xrunner wrote in post #17606409
just was a guess. I mean you could have proper focus on what you focused on but there may just be a very slight focus shift forward but still what you are focusing on is falling in the DOF area giving proper focus on what you are shooitng. but since it might be moved forward its making it look like the 1.8 has more DOF

Hmm... Sounds plausible.
I did not notice it yet, I might be experimenting with it a litlte bit, just for "fun"

urbanfreestyle wrote in post #17606428
i have a feeling i read somewhere this:

If you use f2.8 as a fixed fstop, if you take a shot at 24mm the DOF will be deeper than if you shoot with the same lens at 200mm. so the more zoom, the shallower the DOF?

Yes, more "zoom' from the same distance gives shallower DOF. This really means more magnification means shallower DOF. That is why Macro images have such shallow DOF.