Effect Of 1.6x Crop Sensor On Lens Compression

[decado]

What kind of effect does having a crop sensor have on lens compression? Normal angle of view and compression is at 50mm with a full frame sensor, so if you used a lens at 31mm with a 1.6 crop sensor does that mean it has the same compression of 50mm on a full frame? Or will it be different since you're not getting the full field of view from the lens?

 

[tirediron]

You're correct; taking a 50mm lens as a "normal" lens on a full-frame body, a 31-35 (depending on the exact crop factor) is a normal lens on an APS-C body.

 

[decado]

But what I'm talking about is lens compression, how in wider lenses things look farther apart while with telephoto lenses it makes things seem closer together. How is this affected by a crop sensor?

 

[Garbz]

In exactly the same way as using a wider angle lens or a narrower angle lens.

 

[kundalini]

A little test I ran. Not the best, but nothing else was on offer........

http://www.thephotoforum.com/forum/...rence-between-full-frame-cropped-sensors.html

 

[clanthar]

But what I'm talking about is lens compression, how in wider lenses things look farther apart while with telephoto lenses it makes things seem closer together. How is this affected by a crop sensor?

"Lens compression" is not affected by a crop sensor. The rendition of perspective in a photo is a function of only the camera/subject distance and nothing else. Lens focal length is related to the extent that we tend to back up with telephoto lenses and get closer with wide angle lenses. Given two different sensor sizes you need different focal lengths to produce the same angle-of-view. With matched angle-of-views two different photographers will stand back the same distance to photograph the same subject and so render identical perspective in both photographs.

For example, here in St. Louis the Gateway Arch is 630 feet tall. To photograph it with a 24mm lens on a 35mm camera you'd have to stand back 424 feet. To take the same photo with a 165mm lens on your 8x10 camera you'd have to stand back 424 feet.

Joe

 

[djacobox372]

The "compression," or "perspective/foreshortening" is only affected by the camera's distance to the subject, the focal length has nothing to do with it.

Of course a crop sensor may require you to back up a little to achieve the same composition at any given focal length, which will affect the "compression." It is not caused by the sensor or the lens, only by the change in distance to the subject.

There's a similar relationship to DOF, as DOF is smaller when the focus distance is shorter. So if you have to back up to take a photo with a crop sensor, you will also be increasing the dof because of the further distance to the subject. This is why a 50mm f1.4 has a seemingly smaller DOF on a full-frame camera compared to a crop sensor.

One way to think about this issue, is that the "compression" is changing the relationship of objects in a composition, background objects can be obscured in one shot and visible in another if the "compression" is different. Now we all know it's impossible to magically "look around" an blocking object without moving your eye/camera. You must move the position of the camera to perform such a task. There's a trick shot used in movies all the time where they dolly the camera towards or away from the subject while changing the zoom of the lens to compensate for the composition, the result is the compression changing while the main subject stays the same size on screen. The compression change is caused by the moving of the camera, and the composition is compensated for by changing the focal length.

 

[Garbz]

/edit: redundant, and wrong, and I think it's bed time for me. I hope now one saw this

 

[syphlix]

crop factor doesn't affect compression... that's only affected by focal length... crop factor just makes it so u see less in terms of the frame...

 

[clanthar]

crop factor doesn't affect compression... that's only affected by focal length... crop factor just makes it so u see less in terms of the frame...

"Compression" is not a function of focal length. From the same camera position two different focal length lenses will yield the same perspective. Just like crop factor, changing lens focal length changes what you see in the frame. The relative size and spatial relationship between objects in a photograph can only be altered by moving the camera.

Joe

 

[table1349]

Crop factor has nothing to do with it.
Understanding Camera Lenses

 

[Garbz]

Crop factor has nothing to do with it.
Understanding Camera Lenses

Unless you're trying to get the same picture in which case when you bolt your 50mm on your crop factor camera then you need to step further away from the subject and the result is more compression in the final picture.

Saying it has nothing to do with it is disingenuous given the assumption of wanting x subjects in y positions of the frame and having z focal length to do it. Put a different camera in there you'll need to move and thus the compression is affected.

 

[table1349]

Crop factor has nothing to do with it.
Understanding Camera Lenses

Unless you're trying to get the same picture in which case when you bolt your 50mm on your crop factor camera then you need to step further away from the subject and the result is more compression in the final picture.

Saying it has nothing to do with it is disingenuous given the assumption of wanting x subjects in y positions of the frame and having z focal length to do it. Put a different camera in there you'll need to move and thus the compression is affected.

Which still has no effect on the physical characteristics of the lens. The lens perspective is still present. You only record the center portion of the field of view. Mixing apples and oranges only get us an fruit salad. :mrgreen:

 

[syphlix]

crop factor doesn't affect compression... that's only affected by focal length... crop factor just makes it so u see less in terms of the frame...

\The relative size and spatial relationship between objects in a photograph can only be altered by moving the camera.

Joe

um

thats not true

if i stick my body on a tripod, stick a 100mm prime on it, have 2 objects, 1x 20 ft away and 1x 40 ft away...

when i change to a 24mm prime, both objects will look farther away, and they will look farther apart than with the 100mm

if u move the camera so that the closer object is the same size in both, then then 24mm will make the second object look farther away and smaller than the 100... am i misunderstanding you?

 

[3bayjunkie]

Think of it this way. It is about the same effect as putting a 1.6x Teleconverter on your camera. That is pretty much what it does. the compression is the same but it crops off the edges of your lens so you don't get as dramatic of an effect as far as field of view goes.