Image courtesy of Joao Faclix
f-Stop range
A real camera lens has a minimum and maximum f-Stop range of about f1.2 - f22. The Maxwell camera doesn't have this limitation but it is still recommended to keep the f-Stop range within realistic limits. When rendering very small objects such as jewelry you might set the fstop very high (f100) to avoid any blurring due to depth of field. This however means you have to make your emitters very extremely bright to compensate the much lower exposure, which could lead to problems in noise and unexpected behavior with emitters of several hundred of thousands of watts in power. It is suggested instead to use a more realistic f-Stop range and raise the ISO and/or increase the size of your object if it's really small. Such small changes in size will have a minimal impact on the shading of the object.