I'm saying that the perspective of a 6x7 camera with a 90mm lens is about the same perspective as a 50mm lens on a 35mm camera. The only difference is that the 6x7 camera with a 90mm lens has less depth of field than a 50mm at the same focused distance. Feel free to correct me if I'm wrong.
You mean field or angle of view, not perspective. Perspective depends solely upon one's point or position of view, regardless of format and focal length. Also, since the aspect ratio of 35mm is 3:2 and the aspect ratio of 6x7 is 7:6, focal length/field of view comparisons don't really work.
Using a DOF calculator (Barnack) set at CoC= 0.02mm
35mm format: 50mm f/1.2 lens focused at 2m gives 7cm DOF
6x7 format: 100mm f/4.5 lens focused at 2m gives 14cm DOF
Both lenses have a view angle over the diagonal of the frame of approx. 45 degrees
I don't think any MF lens matches an 50mm f1.2 outside of maybe the contax 80mm f2 (645)or Hasselblad 110mm f2 (6x6), but both I think are incredibly expensive as well as the supporting cameras. For thinnest DOF for the money, then I think that you would want to go with the Pentax 67 105mm f2.4.
But personally, I don't think super thin DOF is necessary and MF bokeh is incredibly smooth. I have an 80mm f2.8 lens but I prefer a little more DOF so I shoot at f4-f5.6 if light permits.
what are the issues with Mamiya ? and what camera(s) are good in your opinion ?
My favorite type of photography is available light portraits so I can't help but pay attention to bokeh.
I am qualified to answer this question because I only use Rolleiflex cameras for reasons that are independent to the bokeh properties.
This is only from what I've read but...
Most MF lenses (Pentax, Mamiya TLR/SLR, Hasselblad, Bronica, etc.) seem to be suitable/good but the Mamiya RF lenses seem to be knocked down the most and also Fuji RF lenses. From what I've read, the Mamiya Rangefinder lenses were designed to be very high contrast and so the bokeh is very busy. Similar with the Fuji RF's (The GF670 is an exception though). Most people believe that the bokeh on these RF lenses are either bad or "suiteable" but nobody really raves about them.
The most hyped MF bokeh for a normal lens typically belongs to:
Rolleiflex 80mm f2.8,
Nikkor 80mm f2.8 (Plaubel Makina), and
Hasselblad 110mm f2.0 (really expensive though and you need a 200/2000 series Hasselblad).
But these are all very different cameras.
I've had 5 Rollei's from MX-EVS (Tessar) to 2.8E (Planar), and they've all been excellent:
I have no complaints about the bokeh from my Mamiya 180mm f4.5 for my RB67. But that's a different animal than the Mamiya 7 or a Fuji rangefinder. But I do agree overall with msbarnes - the bokeh king in hand-held medium format is the Rollei f2.8 lens.
Both taken with a Rollei 2.8E with the Planar lens.
Thanks. so are you saying that a 6x7 lens of 100mm f4 would be equivalent to a 35mm lens of 50mm f2, but the 6x7 lens wold still provide less DOF ?
Normally they tell you to double the focal length of a lens that you use with a 35mm camera to get what you want with a 6x7 camera. Of course this is an approximation. Also a 6x7 camera's viewfinder and negative are more square than a 35mm camera's so it will still look a bit different. I used a 180mm for tight portraiture on my Mamiya RZ67. It had the same depth of field as my 180mm lens on my Contax 35mm camera. Of couse it had less depth of field than the 100mm that I used for tight portraiture with my Contax.
I'm no lens expert but from my understanding, Bokeh is determined by the lens aperture. The more aperture blades a lens has, the more circular the aperture. Lenses with great Bokeh have a very circular aperture.