After getting the Canon 85mm f1.2 lens for my 6D I found it hard to use in the studio. Of course, outdoors I have more control over the camera because I can increase the speed enough to cut the light back and use the beautiful narrow depth of field that the lens affords me. But in the studio the modeling lights were not bright enough and the flash was ALMOST to much light with the flashes set at their lowest settings.
To get that same beautiful DOF in the studio I needed to cut the light back. So, I added a Tiffen 72mm Variable Neutral Density filter in front of the lens. This is a 2-8 fStop filter so I can adjust it for just about anything in the studio. At f2 it gave me the example shot below. Notice how fast the DOF dropped off because I was at f1.2 on the lens but blocked the light by 2 fStops balancing it all out well with a flash. The flash was still low but not at the lowest setting. This allows me the options to have multipal flashes at different levels to create the moods I want yet still go to f1.2 if I so desire.
Of course, the first 30 shots were pretty much out of focus because I was getting a feel for it. I've found that I can't use the center focus point on the eyes and then re-frame each shot like I normally do. I actually have to move the focus point in the camera to be about where the eyes are in whatever frame I want to have. One at the far end for a full body shot for example and then i can still focus on the eyes. This, of course, is only important under f2 or so.
If I needed to do autofocus but wanted to crank the filter to a much darker setting I would hold the filter ring and turn it to wide open so I could focus and then just before taking the shot I'd rotate the filter to the darker setting. The results were a very warm and creamy set of shots. These examples came from a 2 hour shoot with Michelle were I never changed the camera from f1.2 the whole night and we caught some wonderful shots.
Here is a second example of the beauty of using lower fStops in the studio.
I doubt I'm the first photographer to come to the conclusion that the ND filter can be handy this way...heck, I may be the last one to figure it out. But, I'd never seen anyone talk about using one in studio so I wanted to share my experiance. I'm not sure my ND filter will be coming off my 85mm f1.2 anytime soon.