Hi,
Is it possible to do pinhole shooting with the Mamiya 7ii?
Technically, nearly any camera can be a pinhole camera. AE is to be avoided in general, as reciprocity breaks down in long exposures, and most in-built meters cannot compensate for that. A mechanical shutter or an electro-mechanical shutter that can be strictly controlled for lengthy exposures is best. For that matter, cap-in-hand works perfectly well for such lengthy exposures.
A rangefinder camera has no particular advantage over an SLR, or indeed, a box camera, since there is no focusing or setting exposure on a pinhole (except by the gross expedient of making the hole larger or smaller, or changing the sensitivity of the recording media).
Pinhole exposure times tend not to be conducive to hand-holding, either; so there is also no particular advantage to using a light camera over a heavy one.
Can I made a pinhole from the lens cup of the 65mm lens, and shut via the lens? or is it not a real pinhole shooting?
If I understand you correctly, you propose making a pinhole in the lens cap and then exposing through the standard 65mm lens. If that's what you're saying, then no, it is not 'real' pinhole shooting. It is shooting at an extremely small aperture. I suspect your resulting images will suffer greatly from diffraction, which may render an interesting effect, but they won't be pinhole photographs. This is the reason most lenses do not stop down past f/22 or perhaps f/32 (f/64 for some large-format lenses). Diffraction ruins the image.
Pinhole photographs are made without lenses, period. They take advantage of a curious property of light that acts as a lens would in terms of focusing light. They do not have an 'f-stop' as such, and they cannot be focused. The effect obtained is often desirable.
