LOL - again, today, I have gone out with my D200IR camera and the Helinon 135mm f2.8 lens.
This lens is totally manual. It does not have a chip in it at all, so the camera has no idea what it is that you have just shoved in front of the sensor. I have to set the aperture manually - like in the old days with film when you turned the ring around until the aperture was as open or closed as you wanted it.
I also nearly always shoot in full manual mode, selecting all three of the exposure triangle variables to match my artistic vision.
So I first choose my ISO - to be as low as I can, then I set my aperture, to define the depth of field (DOF) as I want it, finally I set the shutter speed. I only vary this when I need a faster shutter speed than my other setting allow, then I normally will play with the aperture a little before I resort to changing my ISO.
I love sharp images. At least, I love the part of the image that needs to be sharp, to be SHARP, and the rest to fade away into the background. DOF is an important part of my artistic expression.
The following images show light and shadow. The first has a shallow DOF, the second a wider DOF, but focused on the background, not the forground. Both were taken with the D200IR and the Helinon 135mm f2.8.
EXIF data beneath each image.
1/500 at f2.8 ISO 100
1/100 at f8.0 ISO 100