(EOS R) Can I focus -while- holding the Depth-of-Field Preview Button?

Hey all,

I've been using the EOS-R for almost a year and now my only issue with the camera is being unable to focus while using DOF Preview. I've used Canons DSLRs in the past and used the feature frequently. I find it extremely beneficial being able to see what is exactly going to be in focus before I take the photo.

I'm aware that you need to bind DOF Preview to a button, and I've done that. However I'm not able to focus while holding the button down. Making it a really clunky process of repeatedly pressing it as I make adjustments to the focus. Is there anyway of keeping the lens stopped down while focusing?

It works in video mode, so I don't see why this shouldn't be available while taking photos. I am aware that the EOS R keeps the aperture fully open to make it easier for AF, MF, Exposure Simulation, ect...

Any help would be appreciated, thanks guys!

Since focusing stopped down is less precise, perhaps they block focusing whilst stopping down? Most EF lenses have mechanical manual focus, so there the camera is unable to prevent focusing while checking the depth of field.

How is focusing stopped down less precise? I don't understand that concept.

Isn't focusing with the aperture wide open, when really it's going to be a much wider DOF less precise? (As long your aperture isn't set to the lowest possible)

vanillaslice wrote in post #18974751
How is focusing stopped down less precise? I don't understand that concept.

Isn't focusing with the aperture wide open, when really it's going to be a much wider DOF less precise? (As long your aperture isn't set to the lowest possible)

I can think of three reasons.
1. DOF is reliant on image size. When you review an image that is 3" in size, the dof will be different than on an 8x10 print.
2. You don't have enough pixels to accurately assess DOF. Take a blurry image now and shrink it down to a 1mp image. It will look a lot sharper.
3. As you close the aperture you are also making the image darker thus it's much more difficult to assess anything.

vanillaslice wrote in post #18974751
How is focusing stopped down less precise? I don't understand that concept.

Isn't focusing with the aperture wide open, when really it's going to be a much wider DOF less precise? (As long your aperture isn't set to the lowest possible)

Think of focus as 'attaining a certain amount of acceptable fuzziness'...when DOF is 1' deep you can be perhaps 4-5" in error and the camera still thinks 'acceptable enough amount of fuzziness'. (speaking purely for conceptual illustration only, not based upon the actual amount of 'acceptable fuzziness' programmed into a camera!) If the DOF is 100' deep (when focusing stopped down), you might be in error by 30' yet the camera still thinks 'acceptable enough amount of fuzziness', but you are truly 30' in error away from 'optimum' focus point.

I made this illustration a long time ago, but it helps to illustrate DOF

Plus, why would you need that, when you have the focus accuracy pointers in your view finder, if enabled? Secondly, focus peaking is a way better method for seeing most of what will be in focus. Both, in tandem, work pretty well in my opinion.