Controlling blur in Depth of Field

I’m using depth-of-field with a very small camera f stop (as small as 1). I’m getting an out of field blur, but I would like to make it even more blur. Is there a way to increase it without changing the f stop on the camera ? Also, is it better to use the camera depth-of-field function or should I use the one in the override tab of the Render Settings window? Thanks.

f 1 should be enough to get a very blurry out of focus, is your scene scaled correctly?

Also, as we found out, 3ds Max at least gives a very different result when the scene units were other than mm, with mm seeingly correct and
cms for instance being incorrect. I did just test this again to be sure it was the case.

In C4D the correct unit is the default option (cm).

Does it also differ if you change units, or does it do a conversion automatically?
Seems I was a bit mistaken anyway.
I tried with Arnold and the results using cm are the same as with cms using vray, so it’s
the mm scene settings that would have to be incorrect, but only when using Vray.
Arnold renders both exctly the same, so a conversion occurs.

I’m using inches. The drawing was originally imported from Solid Edge as a STEP file. I imported it without checking the scale. It’s actually 8 times bigger than reality. Does this change anything?

Yes, it changes everything. Restore the correct dimension and you will have a realistic effect.

If you have smaller objects and you get close with the camera that it is as “big” as the bigger object, you have more blur if you use the same f-stop. If you don’t want to change the f-stop because this changes also the exposure/brightness of rendering, you can go to exposure in the camerasettings and change to “no exposure” or “exposure value”. Then you are very flexible with using f-stop.