Perspective / Focal Length relationship on Crop / FF

[DoctorJ]

I was doing a Portrait photography course the other weekend and we got talking about the best lens for portraits, the pro demonstrated using everything from 28 - 300 and the differing effects on perspective of the face (ie distortion from elongating features to flattening them etc), what you see in the background and so on. He concluded that on his Canon FF 120mm was the optimum flattering focal length.

My question then is on my crop sensor this should equate to an 80mm lens (I have the Nikon 85 1.8G which roughly equates in terms of focal length). Although this may seem a little @nal I am curious, do the perspective qualities translate in the same way as the focal length?

Put another way, if you use a 300mm on a crop, would it flatten perspective the way a 450mm would on a FF sensor, for example?

 

[Richard King]

He concluded that on his Canon FF 120mm was the optimum flattering focal length.

Right

1. is this for a head-shot, or a full portrait
2. what shooting distance was the demo at

In the real world, the shooting distances vary, and the amount of body included in the shot varies too

 

[DoctorJ]

Head shot and it was in a classroom at Esher college. Understand the optimum lens question is a subjective one, just wondering about the perspective question though, is an 80mm on a crop an exact match for a 120mm on a FF?

 

[Faldrax]

Perspective does not change by putting a lens of a different camera body, all that happens when you use a crop body rather than full frame is you get a cropped version of the full frame image.

Using an 85mm on a crop body to obtain a similar field of view to a full frame body with a 120mm lens (IE both shots of the same subject from the same point) you will get a crop of the image an 85mm lens would give - with the perspective from an 85mm lens, not the perspective a 120mm lens would give from that point.

 

[Richard King]

80mm crop is equivalent to 120mm FF

Choice of 50-200mm for a headshot depends on shooting distance. I would be inclined to grab the 50mm then the 85mm on a crop camera

And then the 85mm then the 120 on a full frame

 

[HoppyUK]

1) Perspective is a function of distance, not focal length. Eg, if you stand back and shoot with a wide lens, then enlarge the centre of the image to match the framing you would have got with a longer lens, perspective will be identical.
2) Perspective gets ugly when you shoot too close, like a couple of feet. It gets much better at four to five, and I like to be at around 5-6ft as this is a) far enough for good perspective, and b) close enough for good communication, without being intimidating. YMMV.
3) Considering the points above, 120-135ish is good on full frame for head and shoulders, 85ish for waist up, 50mm for full length - something around that. Adjust by crop factor for crop format equivalents.
4) As distance increases above 6-ish feet, perspective changes very little. However, longer lenses with a narrower field of view will show less background. Some photographers even use something like a 300/2.8 that includes very little background and combined with shallow depth of field makes the subject really stand out.

 

[DoctorJ]

1) Perspective is a function of distance, not focal length. Eg, if you stand back and shoot with a wide lens, then enlarge the centre of the image to match the framing you would have got with a longer lens, perspective will be identical.
2) Perspective gets ugly when you shoot too close, like a couple of feet. It gets much better at four to five, and I like to be at around 5-6ft as this is a) far enough for good perspective, and b) close enough for good communication, without being intimidating. YMMV.
3) Considering the points above, 120-135ish is good on full frame for head and shoulders, 85ish for waist up, 50mm for full length - something around that. Adjust by crop factor for crop format equivalents.
4) As distance increases above 6-ish feet, perspective changes very little. However, longer lenses with a narrower field of view will show less background. Some photographers even use something like a 300/2.8 that includes very little background and combined with shallow depth of field makes the subject really stand out.

Thanks Richard, that explains exactly what I was trying to figure out