portriats

[Alexr25]

...camera to subject distance both of which will affect the perspective in the portrait are a function of sensor size...

Could you explain that?

Perspective distortion (photography) - Wikipedia, the free encyclopedia

 

[tirediron]

I understand what is meant by perspective distortion, what I don't understand is how camera to subject distance is a function of sensor size.

 

[table1349]

 

[tirediron]

Can I have extra butter?

 

[table1349]

Can I have extra butter?

Me thinks that this might be useful for some peoples understanding. Digital Photography Tutorials

 

[Derrel]

My favorite Nikon lenses for full body portraits? Depends on the camera-to-subject distance I am at, and what I want the photos to look and feel like. If I want deep depth of field, and a wide "environmental" view, my favorites would be the 24/2.8 AF-D (seldom, but sometimes); the 35mm f/2 AF-D quite often for environmental portraiture; the 45mm f/2.8-P Nikkor actually MUCH better than any 50mm I own, and one I am using more and more as time goes on; 85/1.4 AF-D, the 70-200 VR-1 for a decade, now the 80-200/2.8 AF-S. I will use the 135 Defocus Control lens too, probably ought to use it more, have started using zooms more and more for portraits since 2007.

Going through my full-frame EXIF data, I find a lot of shots on the zoom done at 127 to 145mm, and also a LOT at 200mm on full length shots where I want a NARROW ANGLE of view ***behind*** the subject.

Indoors, I trend more toward the 35/45/85 primes. Outdoors, more toward 127-200mm on a zoom.

 

[Alexr25]

I understand what is meant by perspective distortion, what I don't understand is how camera to subject distance is a function of sensor size.

Can you understand how sensor size affects the angle of view?
If you do then it should be obvious by simple geometry that for a given subject and focal length to fill the frame the camera to subject distance must change if the sensor size changes.

 

[jaomul]

I understand what is meant by perspective distortion, what I don't understand is how camera to subject distance is a function of sensor size.

Can you understand how sensor size affects the angle of view?
If you do then it should be obvious by simple geometry that for a given subject and focal length to fill the frame the camera to subject distance must change if the sensor size changes.

I understand what you mean. This topic gets covered regularly and often is pulled up by the terminology. I'm not even sue how to word it correctly.

If you use a different format camera you generally use different focal length lenses to get a similar look at similar distance. Where an fx guy/girl may use a 135mm, a dx guy/girl may use an 85mm, as that gives a similar but not quite identical field of view.

I disagree that focal length is just focal length irrelevant of format. Focal length is based on the 35mm (fx) format, but it requires different positioning relative to subject on each format to give a similar framing or look

 

[table1349]

I understand what is meant by perspective distortion, what I don't understand is how camera to subject distance is a function of sensor size.

Can you understand how sensor size affects the angle of view?
If you do then it should be obvious by simple geometry that for a given subject and focal length to fill the frame the camera to subject distance must change if the sensor size changes.

Which has nothing to do with sensor size and everything to do with choices made by the photographer. Photography is not about geometry it is about physics and the physics of photography has not changed. Focal length is focal length.

 

[Alexr25]

Which has nothing to do with sensor size and everything to do with choices made by the photographer.

Which choices are these? Do you mean choice of angle of view, or choice of subject distance or maybe the choice perspective? If it's any these then you need to know both your focal length AND sensor size to make an informed choice.

Photography is not about geometry it is about physics and the physics of photography has not changed.

This shows a sad lack of understanding of both photography and of physics. Much of physics involves geometry and photography covers many disciplines, optics, mechanics, electronics, even chemistry. At the present we are talking about optics and optics is mostly about geometry. How do you think they design new lenses, they use ray tracing programs which are based on geometry.

Focal length is focal length.

I often see this statement made by people who don't understand optics and just parrot what they have read on the internet.
You need to know both the focal length AND sensor size to know whether you are dealing with a wide angle, normal or telephoto lens. For example a 85mm lens on a FF DSLR is a shortish telephoto lens and regarded as good for portraits. Mount it on a medium format camera and it would act like a normal lens (equivalent to 50mm on a FF DSLR), on a large format camera (4X5) a 85mm lens would act as an ultra-wide angle lens (equivalent to approx. 20mm on a FF DSLR) and be totally useless for portraiture.
So while "Focal length is focal length" is true it is a totally meaningless statement. To make informed decisions about which lens to use you have to know the sensor size since the combination of focal length and sensor size determine the lens angle of view.

 

[Derrel]

For several years here on TPF, I have been making reference to the way that sensor size impacts focal length AND it also has an impact on the amount of depth of field and the degree of blurring to the background. Here is the scenario: we have a Canon 85mm 1.8 EF lens. We want a full-length portrait of a six foot tall man, with some room below his feet and above his head. Let's say we want a "tall" picture, and we want the height of the framed area to be 8.47 feet.

With a Canon 7D or 7D-II or Canon Digital Rebel model and its 1.6x size sensor, we MUST position the camera at 34.25 feet away from the man. With a full-frame Canon 5D-series camera, we woulds place the camera only 20 feet away from the man. Depth of field is substantially different between the two cameras, and the two photos.

Depth of Field and the Small-Sensor Digital Cameras (some fundamentals are explained here very well).

 

[table1349]

You are talking equivalents. 85mm is 85mm period. 135mm is 135mm PERIOD. Sensor size does not change focal length no matter what you want to believe. Sensor size only changes how the photographer chooses to frame a shot. Perspective changes are a result of the photographers choice of framing.

 

[Alexr25]

No one is saying that sensor size changes the focal length but what we are saying is that sensor size determines the lenses angle of view and angle of view determines your framing and subject distance which in turn determine perspective. Your options for "choice" of framing of are going to to be different when you are using a 16mm lens on a crop camera than they would be using the same lens on a FF body.