Shallow DoF w/ wide angle lenses: 645 vs. 35mm

[fju]

I am interested in trying a MF camera, most likely a Pentax 645, but have a question regarding achieving a shallow depth of field. When

shooting 35mm film, I prefer using fast 28mm or 35mm lenses, wide open, to achieve a (somewhat) shallow DoF.

 

I was looking at an online calculator to determine whether or not I could get a more shallow DoF from a medium format camera than what I

can get from a 35/1.4 lens on 35mm. According to the site "http://www.dofmaster.com/dofjs.html" I cannot.

 

The numbers I put in were:

 

35mm lens, f/1.4 aperture for 135 = DoF 2.11 ft.

 

55mm lens, f/2.8 aperture for 645 = DoF 2.56 ft.

 

60mm lens, f/3.4 aperture for 6x6 = DoF 2.55 ft.

 

These assume a subject distance of 10 ft.

 

Thoughts?

[mike_earussi1]

For a given f stop MF has a shallower dof than 35mm but because MF lenses are slower you'll wind up getting about the same. For 645 add about 1 1/2 stops to equal 35mm, i.e.the dof at f1.8 in 35mm would aprox equal the dof at f2.8 in 645. The only lens that you might get a shallower dof in MF is the Mamiya 80 f1.8, but it's not wide angle.

[stuart_richardson]

If shallow depth of field with a wide angle is your objective, you would probably be better served by 6x7 than 645 -- the

65mm f/4 on the Mamiya 7II has reasonably shallow depth of field. But if you really want wide with shallow depth of field, 35mm probably

has the greater range of options -- 35mm f/1.4, 35mm f/1.2 (voigtlander nokton for Leica M), 40mm f/1.4 (voigtlander), 28mm f/1.4 (nikon),

28mm f/2 (Leica,

various others), 24mm f/1.4 (Canon, now Leica), 21mm f/1.4 (Leica).

[fju]

Thank you fro the responses. They were very helpful.

[dave_redmann]

Assuming you are printing to US-standard sizes like 8x10, 11x14, and 16x20 inches, for any given angle of field and aperture, 645 has between 1.5 and 1.67 stops less depth of field than 35mm (or "full-frame" DSLR's), and 6x7 has between 2.33 and 2.5 stops less.

 

From this, you see that, for example, for a given angle of view, an f/2.8 lens on a 645 has about the same minimum depth of field as an f/1.6 or f/1.7 lens on a 35mm, and an f/4 lens on a 6x7 has about the same depth of field as an f/1.7 or f/1.8 lens on a 35mm.