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Archive 2016 · A Question of Perspective Compression on Different Sensor Sizes

  
 
Sener
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p.1 #1 · p.1 #1 · A Question of Perspective Compression on Different Sensor Sizes


Hi all,

I have an A7ii with some lenses. For travel, I was considering to get an A6000 to use my CZ 1.8/55 as a mild tele. The plan is to have 28mm and 85mm angles ready in two cameras as a light travel kit.

I like to creatively use perspective compression. It comes very handy in shooting some landscape and cityscape images. Also in street shots, to some degree.

Then this question of perspective compression hit me. A FF 55mm lens is genuinely designed as an 55mm lens for a 36*24mm sensor. Therefore it should have the optical qualities of a FF 55mm lens on any sensor size. Therefore if I put it in front of an APS-C sensor, it will not give me the perspective compression of an 85mm lens used on a 36*24mm sensor (82.5mm, to be exact). The sensor will just provide me a cropped version of the lens' projection on it, and the perspective compression will not be 85mm-on-FF equivalent.

Or will it?

Apart from the purpose of this topic, I also wonder how this perspective compression works in different sensor sizes and the lenses designed for these sensors. For example, does a 12mm lens, designed for a 17*13mm m43 sensor, have a perspective compression equivalent to that of a 12mm lens designed for FF, or a 24mm lens designed for FF?

Thanks and have a nice day.



Dec 27, 2016 at 07:55 AM
rdeloe
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p.1 #2 · p.1 #2 · A Question of Perspective Compression on Different Sensor Sizes


Focal length doesn't change based on the sensor. So a 55mm lens has the same optical characteristics on any camera to which it is attached. However, what changes is the field of view. Have a look at this comparison table (ignore the fact that it's Nikon specific -- doesn't matter). https://www.nikonians.org/reviews/fov-tables

Rather than thinking about perspective compression as a relative concept, head on over to a depth of field calculator and see what happens for the same focal length on different sensors at different apertures and focusing distances. For example, I like this one: http://www.dofmaster.com/dofjs.html In trying to sort this out for myself (I use medium format lenses on an A7r sensor) I've found this approach (look at the numbers) to be very useful.

Good luck with this.



Dec 27, 2016 at 08:04 AM
jcolwell
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p.1 #3 · p.1 #3 · A Question of Perspective Compression on Different Sensor Sizes


Mumble, mumble, mumble...

Edited on Dec 28, 2016 at 07:11 AM · View previous versions



Dec 27, 2016 at 08:06 AM
Sener
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p.1 #4 · p.1 #4 · A Question of Perspective Compression on Different Sensor Sizes


rdeloe wrote:
Focal length doesn't change based on the sensor. So a 55mm lens has the same optical characteristics on any camera to which it is attached. However, what changes is the field of view. Have a look at this comparison table (ignore the fact that it's Nikon specific -- doesn't matter). https://www.nikonians.org/reviews/fov-tables

Rather than thinking about perspective compression as a relative concept, head on over to a depth of field calculator and see what happens for the same focal length on different sensors at different apertures and focusing distances. For example, I like this one: http://www.dofmaster.com/dofjs.html In trying to sort this out
...Show more

Thank you rdeloe,

We already know the FOV differences between different sensor sizes. But this is not the subject of this topic specifically. Also I was hoping to resolve this without ever bringing FOV or DOF onto the table.

But if perspective compression cannot be explained without going through the DOF-equivalence shenanigans, so be it



Dec 27, 2016 at 08:12 AM
arduluth
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p.1 #5 · p.1 #5 · A Question of Perspective Compression on Different Sensor Sizes


Perspective is purely a function of distance to subject. That's it.

Compression is an element of perspective, which depends on having a bit of distance from the subject. It's not a property of the lens or format.

Different formats give a different field of view for the same focal length, assuming the lens has a image circle large enough to cover all the formats under discussion.

Using a a 50mm on APS-C will have the same field of view and the same "perspective compression" as a 75mm lens on full frame. No difference in that regard.




Dec 27, 2016 at 09:32 AM
petrochemist
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p.1 #6 · p.1 #6 · A Question of Perspective Compression on Different Sensor Sizes


Perspective compression is all to do with the relative distances from the viewer..

Take a situation with two lampposts 100m apart. If these are photographed from a position 100m from the nearest the further one will be twice as far away. This might be the sort of view of them that we would normally see, where the further one is half the size & looks twice as far away.

If we move away by 900m the further one is only 10% further than the near one. Using a long lens (or cropping the image, printing bigger, viewing closer etc) to enlarge the nearest to a size similar to what it had in the closer view we get the closest looking much the same as in the first case but the further one only looking 10% smaller/further away. This is all there is to perspective changes.

Taking the shot from the further location & not enlarging the image will show just the same perspective & compression, but unless the image is altered to be bigger it looks further away & so isn't different from how we are used to seeing things.



Dec 27, 2016 at 11:49 AM
Jman13
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p.1 #7 · p.1 #7 · A Question of Perspective Compression on Different Sensor Sizes


jcolwell wrote:
Correct.


Not correct. As a few others later posted, perspective compression is solely a function of distance, and has nothing to do with the focal length. A 55mm shot on APS-C and an 85mm lens on FF from the same spot will yield images with the same perspective. DOF may be different if you don't compensate for aperture, but perspective will be the same.

An article I wrote a while back with samples on this very subject: http://admiringlight.com/blog/perspective-correcting-myth/



Dec 27, 2016 at 02:15 PM
drewmey
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p.1 #8 · p.1 #8 · A Question of Perspective Compression on Different Sensor Sizes


I think the key point here is that when putting the lens on a crop body, the user will be forced to step back to get the same items/objects/subjects within the frame. In doing so, perspective compression will occur...due to the sensor size? No. But will it happen...in the real world use? Yes.

If you ask someone with a background in physics, math, etc. this questions...they will tell you there is no perspective compression when sensor size changes because they know (rightly) that the formulas/physics tell them so.

If you ask someone with a strictly artistic photography background this question....they will tell you there is going to be perspective compression when sensor size changes because they know (rightly) that in reality you WILL change distance from the subject(s) to get the same information within the frame.

If you want to know the physical reality of this world, read my first example. If you want to know what you will experience when you buy an A6x000 read my second example because you will begin standing farther away from things with that crop body.



Dec 27, 2016 at 02:55 PM
Jman13
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p.1 #9 · p.1 #9 · A Question of Perspective Compression on Different Sensor Sizes


You're correct. However, often the exact opposite is what is thought as part of the misconceptions in this area. The misconception between focal length and distance often presumes that someone shooting a 40mm lens on Micro 4/3 will have less compression than someone shooting an 80mm lens on full frame, which is false. And using the SAME lens on a smaller format, as you note, will likely lead to an increase in compression in the photo due to the need to stand back further to frame the subject the same.


Dec 27, 2016 at 02:59 PM
rw11
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p.1 #10 · p.1 #10 · A Question of Perspective Compression on Different Sensor Sizes


DoF will change and can sometimes make 'looks' like a perspective change.


Dec 27, 2016 at 03:05 PM
Sener
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p.1 #11 · p.1 #11 · A Question of Perspective Compression on Different Sensor Sizes


Thanks for your valuable input so far.

Just a little note, I am not moving forward or backward when using the 55mm on APSC. Consider that I'm having in one hand i have the A7ii+85mm FF lens, and in the other i have the A6k+55mm FF lens. And I am staying in the same spot while using either. So FOVs would be the same (negliging the 2.5mm difference on the A6k combo). But will perspective compression be? That was my original question.

I'm still digesting the more technical answers, so forgive me if I skipped something.



Dec 27, 2016 at 03:05 PM
JohnJ
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p.1 #12 · p.1 #12 · A Question of Perspective Compression on Different Sensor Sizes


To reiterate comments made by others, perspective is ONLY determined by the position of the lens relative to the subject, NOT by the lens or the sensor.

A wider lens forces you closer, a longer lens forces you further if filling the frame with the same subject, so changing your position, not the lens, changes perspective.



Dec 27, 2016 at 03:24 PM
WhyFi
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p.1 #13 · p.1 #13 · A Question of Perspective Compression on Different Sensor Sizes


Sener wrote:
Thanks for your valuable input so far.

Just a little note, I am not moving forward or backward when using the 55mm on APSC. Consider that I'm having in one hand i have the A7ii+85mm FF lens, and in the other i have the A6k+55mm FF lens. And I am staying in the same spot while using either. So FOVs would be the same (negliging the 2.5mm difference on the A6k combo). But will perspective compression be? That was my original question.

I'm still digesting the more technical answers, so forgive me if I skipped something.


If you're not moving, your perspective isn't changing, regardless of sensor format, focal length, FoV, etc. The position of the camera relative to the subject is the only thing that influences perspective.




Dec 27, 2016 at 04:00 PM
arduluth
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p.1 #14 · p.1 #14 · A Question of Perspective Compression on Different Sensor Sizes


WhyFi wrote:
If you're not moving, your perspective isn't changing, regardless of sensor format, focal length, FoV, etc. The position of the camera relative to the subject is the only thing that influences perspective.



Exactly. If you have an A7 with a 70-200mm zoom and take one photo at 70mm, zoom in, and take another at 200mm. The 70mm and 200mm photos will have the same perspective and the same amount of compression. Since you didn't move, the 200mm shot will have less in the frame than the 70mm shot, but that's a different kettle of fish than perspective.

Same with your A7+85mm and A6000+55mm. The field of view will be marginally wider on the A6000+55mm, but perspective and compression will be the same.



Dec 27, 2016 at 04:49 PM
U.C.
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p.1 #15 · p.1 #15 · A Question of Perspective Compression on Different Sensor Sizes


If you don't change your distance, perspective doesn't change:


Perspective by Universal Creations, on Flickr



Dec 28, 2016 at 02:20 AM
rdeloe
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p.1 #16 · p.1 #16 · A Question of Perspective Compression on Different Sensor Sizes


Very nice U.C.! The pictures say it all.


Dec 28, 2016 at 10:48 AM
notherenow
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p.1 #17 · p.1 #17 · A Question of Perspective Compression on Different Sensor Sizes


Why not just shoot your camera and lens in both FF and APSC mode and see?

If necessary resize them to the same size.



Dec 28, 2016 at 01:57 PM





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