You like 85mm at 9' distance for 135 format head and shoulders; 85:24 = 3.55:1. Use
- 150mm (3.55 * 43) on 645
- 200mm (3.55 * 56) on 6x6 or 6x7
- 320mm (3.55 * 90) on 4x5"
- 65mm (3.55 * 18) on half frame (e.g. Olympus Pen)
You like 150mm at 9' distance for 135 format headshot; 150:24 = 6.25:1. Use
- 270mm (6.25 * 43) on 645
- 350mm (6.25 * 56) on 6x6 or 6x7
- 560mm (6.25 * 90) on 4x5"
- 110mm (6.25 * 18) on half frame (e.g. Olympus Pen)
...results identical framing and identical perspective at the identical subject distance
choosing the closest real FL lens.
I was too expensive for the company's taste so after two months they went to iPhone shots with the guys covering their balls again, oh well.
In terms of distance to control perspective, just look at this shot by HCB and the way he makes his viewpoint of the line on the wall equal the angle on the cart.
The technical term is "positive feedback".
I am a wedding photographer, so I like to always take a few shots up close just of the details. The way the hand rests on the should, the way the earring hangs next to her next. The bride holding the bouquet. So I can get really close, but I know this breaks a certain measure of personal space so I make those moments fast.