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Perspective and sensor size
Old 01-09-2017   #1
marcr1230
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Perspective and sensor size

Probably a dumb question but here goes

I know that the field of view is dependent on sensor size and focal length

So generally speaking a 25mm lens give the same FOV on a 1/2 size sensor ( like micro 4/3) as a 50 does on a FF sensor from the same distance

So the question is - with respect to portraits and people

Can you tell the difference between the 2 ? Are there
Perspective or depth of field diffs or otherwise?

Thanks
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Old 01-09-2017   #2
MIkhail
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Any given lens draws the same regardless of what sensor you put behind it.
It's just for full sensor you see more of the picture it draws, the APC cuts out some from edges.
So one should not be able to tell the difference between two portraits taken with the same lens on two different cameras, one full frame and one cropped sensor, provided that you walked closer to the subject with the full frame camera.
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Old 01-09-2017   #3
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As you say, Marc, FoV is different. A 25mm on µ4/3 shows the same angle as a 50mm on FF.

And the DoF is different. If you shoot a 25mm on µ4/3 at aperture f/2.8 it will show a similar DoF as a 50mm on FF at f/5.6.

(But when shot with the same ISO setting, the shutter speed will be like an f/2.8 on FF. No difference there.)
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Old 01-09-2017   #4
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Quote:
Originally Posted by MIkhail View Post
Any given lens draws the same regardless of what sensor you put behind it.
It's just for full sensor you see more of the picture it draws, the APC cuts out some from edges.
So one should not be able to tell the difference between two portraits taken with the same lens on two different cameras, one full frame and one cropped sensor, provided that you walked closer to the subject with the full frame camera.
I think he means to compare a 25mm on µ4/3 and a 50mm on FF. There is a difference.

And if you use the same lens but walk closer, you will also generate different DoF. DoF will be roughly the same, though, if you crop the FoV after the shot in post-production.
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Old 01-09-2017   #5
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This is same lens different sensors - I agree that if you have the same subject to camera distance - the smaller sensor will just be have a center crop of the larger sensor image

If you move closer though to the subject - to provide the same portrait of the subject - the background will be closer / further and these be different

However my question is more differs lenses different sensors but overall same FOV



Quote:
Originally Posted by MIkhail View Post
Any given lens draws the same regardless of what sensor you put behind it.
It's just for full sensor you see more of the picture it draws, the APC cuts out some from edges.
So one should not be able to tell the difference between two portraits taken with the same lens on two different cameras, one full frame and one cropped sensor, provided that you walked closer to the subject with the full frame camera.
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Old 01-09-2017   #6
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Quote:
Originally Posted by Kent View Post
DoF will be roughly the same, though, if you crop the FoV after the shot in post-production.
Yes, sorry. You are right.
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Old 01-09-2017   #7
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Quote:
Originally Posted by marcr1230 View Post
Probably a dumb question but here goes

I know that the field of view is dependent on sensor size and focal length

So generally speaking a 25mm lens give the same FOV on a 1/2 size sensor ( like micro 4/3) as a 50 does on a FF sensor from the same distance

So the question is - with respect to portraits and people

Can you tell the difference between the 2 ? Are there
Perspective or depth of field diffs or otherwise?

Thanks
Basic rules:
  • Perspective is a function of distance.
  • Field of View is a function of focal length and format.
  • Depth of field is a function of physical lens opening and distance setting for a given field of view.

From these basic rules you can deduce the following relationships:
  • Two different format cameras with the same lens will present different views of the subject.
  • Two different format cameras with a lens that matches the field of view between them will present the same view of the subject.
  • In both cases, the perspective of the subject (the relationship of near and far elements in the frame) will be the same if the subject to camera distance is the same.
  • The depth of field of the camera with the smaller format sensor with the same field of view will be greater than that for the larger format camera at the same f/number.
  • The depth of field of the camera with the smaller field of view will be less than that of the camera with the greater field of view at the same f/number.

G
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Old 01-09-2017   #8
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I found a good link that shows the differences and equivalences - thanks everyone

https://www.pointsinfocus.com/tools/...=50&dst=5&u=us
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Old 01-10-2017   #9
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Quote:
Originally Posted by Godfrey View Post
Basic rules:
  • Perspective is a function of distance.
  • Field of View is a function of focal length and format.
  • Depth of field is a function of physical lens opening and distance setting for a given field of view.

From these basic rules you can deduce the following relationships:
  • Two different format cameras with the same lens will present different views of the subject.
  • Two different format cameras with a lens that matches the field of view between them will present the same view of the subject.
  • In both cases, the perspective of the subject (the relationship of near and far elements in the frame) will be the same if the subject to camera distance is the same.
  • The depth of field of the camera with the smaller format sensor with the same field of view will be greater than that for the larger format camera at the same f/number.
  • The depth of field of the camera with the smaller field of view will be less than that of the camera with the greater field of view at the same f/number.

G
These are the points one needs to consider. Sensor area alone has no intrinsic affect on perspective.

It can be useful to start off thinking about this topic keeping the camera-to-subject difference constant. For each sensor area you happen use, there will be a lens that will produce images with essentially identical perspectives, fields of view and DOFs. Of course these lenses must have different focal lengths and be set to different apertures.
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Old 01-10-2017   #10
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Quote:
Originally Posted by MIkhail View Post
Any given lens draws the same regardless of what sensor you put behind it.
It's just for full sensor you see more of the picture it draws, the APC cuts out some from edges.
So one should not be able to tell the difference between two portraits taken with the same lens on two different cameras, one full frame and one cropped sensor, provided that you walked closer to the subject with the full frame camera.
That underlined part is wrong. Once you walk closer to the subject you change your perspective i.e. you change the foreground-background ratio in the image.
So if you use the same lens but walk closer, is not the same as using the same lens and cropping the image.

Unless your subject is at infinity and there's nothing closer that is visible
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Old 01-10-2017   #11
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Quote:
Originally Posted by Pherdinand View Post
That underlined part is wrong. Once you walk closer to the subject you change your perspective i.e. you change the foreground-background ratio in the image.
So if you use the same lens but walk closer, is not the same as using the same lens and cropping the image.

Unless your subject is at infinity and there's nothing closer that is visible
I know. See my reply above.
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