Yes,indeed u can!
The Nikon FG.It has manual,aperture priority,and auto exposure.
I don't know the D300, but similar Nikon DSLRs have a secondary control dial on the front, not far below the shutter button.
A Nikon EM has a standard Nikon mount, so you can use any lens that'll fit on a Nikon, except for a Nikon Series G lens, on an EM. A Series G will fit but it won't work because there's no aperture ring.
What lens are you using? It is probably because your lens has a very narrow maximum aperture.
Yes--but only in manual mode, so you'll have to set your own aperture and shutter speed.
Yes, you can. Nikon uses Nikon F-mount to connect the lens to the camera. Sometimes other manufacturers change their mount, but Nikon never did, so you can still even use analog lenses.
What lens? If your D3100 is using an f/5.6 (or f/5.8) aperture lens, that's as far as you can stop it down.
Most lenses are identified by their zoom range and aperture. A Nikon Nikkor 70-200mm VR II f/2.8 is a lens with a 70-200mm zoom range, Vibration Reduction II, and a maximum fixed aperture of 2.8 - in other words, a very expensive fast pro lens. A Nikon Nikkor 70-200mm VR f/4-5.6 offers the same optical range, but nowhere near the optical quality in low light situations because of its variable aperture and consumer grade quality.
No
No. The cool pix series does not have interchangeable lenses.
Generally, you can with all cameras. All you need is a shallow depth of field. You can achieve this by using a low aperture (ex. f/2.8, f/1.8) The lower the f/#, the shallower your depth of field will be.
Set the date before this.