MF enlargement factor

[Kev M]

Enlargement factor as in opposite of crop factor. I was just thinking to myself about field of view and how everyone likes a 50mm on a DSLR (cropped) as it mimics 75mm on a 35mm camera which is a nice length for portraits and how I'd just been given a Lubitel which actually has a 75mm lens and how lucky I am and then it dawned on me.

75mm on MF can't be anywhere near 75mm on a 35mm camera. I know the physical focal length doesn't change as such but it's the effect the lens has on distorting a picture from wide to tele so what is a 75mm MF lens like/good for and what is the MF ideal focal length/FOV for portraits?

 

[joxby]

75-80mm is a standard lens on M/F, about 50 on a 35mm.
50mm is a wide angle lens on M/F
for portraits on M/F, you can use 75mm, its neither wide nor telephoto so there is little distortion, but you will be pretty close to your subject.
You could do with 135, 150 or 200 for a bit of elbow room for portraits M/F

 

[Chappers]

The "Standard " focal length is the diagonal length across the frame ( In round terms).
So a medium format camera using 120 film (12 on) has a negative size of 6 cm . Quick bit of school boy maths gives you a focal length of 84 mm. OK rounding that gives you about 80mm. 75mm will give you a very slight wide angel but not enough to worry about.

The 135 would make a nice portrait lens, but if you have the room the 150 would be better.

 

[nobody]

The diagonal length of 35 mm format (24 mm X 36 mm) is 43.27 mm. The focal length of 75 mm is 1.73X of 43.27 mm.
So, the diagonal length of 6X6 format (56 mm X 56 mm) is 79.20 mm. So your ideal portrait focal length should be 79.20 mm X 1.73 = 137.28 mm.

Hope this help!