# How does lens perspective work on a mirrorless camera?



## PaulWog (Sep 23, 2013)

Take, for example, the Nikon 1 J3 (my girlfriend has this camera). I would assume her 10-30mm lens at 10mm doesn't have the same compression or distortion as a 10mm lens on 35mm DSLR format?

I'm curious how to calculate how things differ. What lens would provide her with the same background-to-subject compression that, say, an 85mm lens on a DSLR would provide? I realize a 34mm focal length would provide the same reach, but what would provide the same background compression. 

I'm just completely lost about this.


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## runnah (Sep 23, 2013)

IIRC it's about the sensor size rather than the addition of a mirror.


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## KmH (Sep 23, 2013)

Yep. Mirror or no mirror doesn't factor. 

The smaller the image sensor the greater the crop factor. The larger crop factor gets the smaller the field-of-view for any given focal length.

Nikon 1 uses Nikon's CX size image sensor and has a crop factor of 2.7x.

http://www.tawbaware.com/maxlyons/calc.htm


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## PaulWog (Sep 23, 2013)

So how would a 10mm (27mm equivalent) differ from a 27mm on FF? I thought I got it all.


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## Gavjenks (Sep 23, 2013)

Perspective (which things appear to line up at different depths, and how large things are relative to one another in the image) has absolutely nothing to do with lenses, or sensor size, or flange to focal distance, mirrors, anything.  It is 100% dependent upon your distance to the subject. At 10 feet from the subject, your perspective will be identical regardless of whether you're using a mirrorless camera with a 400mm lens, or a cardboard box pinhole camera with a 10"x14" sheet of film in it, or a human eyeball.

If that's not what you mean, then please explain in a different way what you do mean.



(Also, perspective is not a "distortion" which is partly why I'm hesistant that is what you mean for sure)


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## PaulWog (Sep 23, 2013)

Gavjenks said:


> Perspective (which things appear to line up at different depths, and how large things are relative to one another in the image) has absolutely nothing to do with lenses, or sensor size, or flange to focal distance, mirrors, anything.  It is 100% dependent upon your distance to the subject. At 10 feet from the subject, your perspective will be identical regardless of whether you're using a mirrorless camera with a 400mm lens, or a cardboard box pinhole camera with a 10"x14" sheet of film in it, or a human eyeball.
> 
> If that's not what you mean, then please explain in a different way what you do mean.
> 
> ...



What I mean is when you shoot one person in front of another with a 24mm lens on full-frame, the person at the back will appear further away from the person in front. When you shoot the same two subjects with an 85mm lens, they will appear closer together. I was calling it "background compression", but I'm not sure what it's called. I generally like using a range between 50 and 200 to get a decent amount of this effect, since I rarely like stretching out the background and making things seem distant.

However, I don't know how lenses translate. From how I understood it, on a DX sensor, you are simply cropping the same image in. So a 50mm shot on DX would be identical to an FX shot, save for being cropped and effectively zoomed in. This would lead me to think that the "background compression" would be the same for a 50mm shot on DX as it would be for a 50mm shot on FX. So what I'm confused about is if I use a 10mm lens on a 2.7x mirrorless camera, would the background seem stretched out a ton even though it should be 27mm equivalent? Or will that "background compression" be the same as a 27mm?

I'm likely mislabeling things, but hopefully I've cleared up what I'm trying to say a bit.


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## Gavjenks (Sep 24, 2013)

Yes, that's the same thing I'm talking about. It's a function of perspective. *If you stand in the same spot*, then the relative apparent size of a person in the foreground and a person in the background will be the same, no matter what lens, focal length, sensor, camera or whatever you use.

It depends 100% on camera location.

At the same camera position, you will get equal "background compression" for instance using a shoebox with film, a mirrorless 10mm lens camera, a disposable drugstore camera, or a DSLR with a 5,000mm lens on it.  Doesn't matter.  How much of the scene you record will change, but not the relative sizes or positions of people in foreground and background.



The reason you associate this affect with focal length, is because naturally, when using a shorter focal length, you walk closer to the person. The walking closer part is what made the difference, NOT the focal length. If you kept that same 24mm lens on your camera and walked back, you'd get the same change in relative size and position of the people as you are used to with the 85mm (they'd just all be tiny in the frame, but relatively changing the same way)


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