Does crop factor affect dynamic perspective/Distortion?

dstructor · 02-09-2013, 11:34 AM

It's known that on an APS-C 1.5x crop sensor a 14mm would give me the equiv. of 21mm on a 35mm/full frame

But what about the dynamic perspective/distortion that a wide angle lens gives? would that too be affected?

Attached: the distortion bet. a 21mm & a 50mm lens
Assuming I attached a 21mm lens to a cropped sensor that gives me the equivalent of 50mm focal length; Would i still see the distortion or not?

Attached Images

JinDesu · 02-09-2013, 12:06 PM - **1 Like**

You see how in the left, the distortion is mostly the parts of the computer that's closest to you, and also towards the edge of the frame? Imagine you take the left image, but take the computer further back. Then crop about 60% of the center. That's what the crop image will give you, and that's how much less distortion it'll give.

Mareket · 02-09-2013, 12:28 PM

As far as I'm aware, distortion like this is related to the distance of the subject, and the relative distance of it's different components. A 14mm on a k-5 for example would have a field of view similar to a 21mm lens or whatever, so you'd have to move backwards to retain a similar amount of the computer in the frame, reducing the ratio of the distances to each part of the computer, and therefore reducing the distortion.

Not 100% sure on that though.

enoeske · 02-09-2013, 12:36 PM

no -- crop factor does not change perspective; only the distance between the subject and the camera does. If you shoot with a 50mm lens to get the image like the 2nd one in the example or you use a 8mm lens from the same spot, the perspective won't change. What will change is the space around the subject. In order to fill the frame with the subject using the 8mm, you have to get in close and that changes your perspective.

stevebrot · 02-09-2013, 12:53 PM

Originally posted by dstructor

It's known that on an APS-C 1.5x crop sensor a 14mm would give me the equiv. of 21mm on a 35mm/full frame

But what about the dynamic perspective/distortion that a wide angle lens gives? would that too be affected?

Attached: the distortion bet. a 21mm & a 50mm lens
Assuming I attached a 21mm lens to a cropped sensor that gives me the equivalent of 50mm focal length; Would i still see the distortion or not?

Not per se. The keystoning in your photos is the result of normal perspective (not distortion). Perspective is based on the position of the lens front element relative to the subject. Move further away and the keystoning is less. Move close and it becomes more pronounced. The media size (crop factor) is only coincidental in that it determines the FOV for a particular distance and focal length lens.

Steve

Na Horuk · 02-10-2013, 01:20 PM

So distortion is a lens property, but perspective distortion depends on how you tilt the lens and how far from the objects it is. Distortion (how the lens bends things) will be the same regardless of sensor size, but a smaller sensor cuts off the borders and so it might appear to be less distorted (because you are looking only at the centre). This distortion can also be fixed in post processing.
Basically, the sensor size doesn't change optical properties of the lens, but it does cut off a bit of the image which gives the illusion. So saying that a given focal length on a crop sensor is "equivalent to.." is just to make it easier for people who come from film.

**Lowell Goudge** · 02-10-2013, 03:28 PM - **1 Like**

Although the answers above are correct, and that crop factor does not impact perspective, only the subject dstance matters, there is a secondary impact of acroed sensor.

Since it changes the fFOV of a lens, you are prone to reposition yourself, and change the distance when using a lens on a corp sensor, therefore you do get a change in perspective, but not directly due to the crop sensor, but because it makes you reposition.

normhead · 02-10-2013, 03:41 PM

So what is a cropped sensor? If you start with the 645 D, FF and everything else is a crop sensor. As I have argued many times, there are just cameras and lenses. You look through the view finder, you find the lens that gives you the FoV you want, you take your picture. It's the same for every camera ever made.

The question, I'd be interested in is "Standing in the same place, does a picture taken with a 50 mm lens on FF look the same as one taken with a 35 mm lens on APS-c, if you expand the APS-c image to be the same size?"

02-09-2013, 11:34 AM	#1
dstructor Senior Member Join Date: Oct 2012 Posts: 139	Does crop factor affect dynamic perspective/Distortion? It's known that on an APS-C 1.5x crop sensor a 14mm would give me the equiv. of 21mm on a 35mm/full frame But what about the dynamic perspective/distortion that a wide angle lens gives? would that too be affected? Attached: the distortion bet. a 21mm & a 50mm lens Assuming I attached a 21mm lens to a cropped sensor that gives me the equivalent of 50mm focal length; Would i still see the distortion or not? Attached Images

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02-09-2013, 12:06 PM - 1 Like	#2
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	You see how in the left, the distortion is mostly the parts of the computer that's closest to you, and also towards the edge of the frame? Imagine you take the left image, but take the computer further back. Then crop about 60% of the center. That's what the crop image will give you, and that's how much less distortion it'll give.

02-09-2013, 12:28 PM	#3
Mareket Veteran Member Join Date: Jun 2011 Location: Chester Photos: Gallery \| Albums Posts: 719	As far as I'm aware, distortion like this is related to the distance of the subject, and the relative distance of it's different components. A 14mm on a k-5 for example would have a field of view similar to a 21mm lens or whatever, so you'd have to move backwards to retain a similar amount of the computer in the frame, reducing the ratio of the distances to each part of the computer, and therefore reducing the distortion. Not 100% sure on that though.

02-09-2013, 12:36 PM	#4
enoeske Veteran Member Join Date: Jul 2009 Location: Surprise, Az Photos: Gallery Posts: 2,136	no -- crop factor does not change perspective; only the distance between the subject and the camera does. If you shoot with a 50mm lens to get the image like the 2nd one in the example or you use a 8mm lens from the same spot, the perspective won't change. What will change is the space around the subject. In order to fill the frame with the subject using the 8mm, you have to get in close and that changes your perspective.

02-09-2013, 12:53 PM	#5
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by dstructor It's known that on an APS-C 1.5x crop sensor a 14mm would give me the equiv. of 21mm on a 35mm/full frame But what about the dynamic perspective/distortion that a wide angle lens gives? would that too be affected? Attached: the distortion bet. a 21mm & a 50mm lens Assuming I attached a 21mm lens to a cropped sensor that gives me the equivalent of 50mm focal length; Would i still see the distortion or not? Not per se. The keystoning in your photos is the result of normal perspective (not distortion). Perspective is based on the position of the lens front element relative to the subject. Move further away and the keystoning is less. Move close and it becomes more pronounced. The media size (crop factor) is only coincidental in that it determines the FOV for a particular distance and focal length lens. Steve

02-10-2013, 01:20 PM	#6
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	So distortion is a lens property, but perspective distortion depends on how you tilt the lens and how far from the objects it is. Distortion (how the lens bends things) will be the same regardless of sensor size, but a smaller sensor cuts off the borders and so it might appear to be less distorted (because you are looking only at the centre). This distortion can also be fixed in post processing. Basically, the sensor size doesn't change optical properties of the lens, but it does cut off a bit of the image which gives the illusion. So saying that a given focal length on a crop sensor is "equivalent to.." is just to make it easier for people who come from film.

02-10-2013, 03:28 PM - 1 Like	#7
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,891	Although the answers above are correct, and that crop factor does not impact perspective, only the subject dstance matters, there is a secondary impact of acroed sensor. Since it changes the fFOV of a lens, you are prone to reposition yourself, and change the distance when using a lens on a corp sensor, therefore you do get a change in perspective, but not directly due to the crop sensor, but because it makes you reposition.

02-10-2013, 03:41 PM	#8
normhead Pentaxian Join Date: Jun 2007 Location: Near Algonquin Park Photos: Gallery \| Albums Posts: 40,451	So what is a cropped sensor? If you start with the 645 D, FF and everything else is a crop sensor. As I have argued many times, there are just cameras and lenses. You look through the view finder, you find the lens that gives you the FoV you want, you take your picture. It's the same for every camera ever made. The question, I'd be interested in is "Standing in the same place, does a picture taken with a 50 mm lens on FF look the same as one taken with a 35 mm lens on APS-c, if you expand the APS-c image to be the same size?"