# Effect Of 1.6x Crop Sensor On Lens Compression



## decado (Dec 27, 2010)

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 (Dec 27, 2010)

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 (Dec 27, 2010)

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 (Dec 27, 2010)

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


----------



## kundalini (Dec 27, 2010)

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 (Dec 27, 2010)

decado said:


> 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 (Dec 27, 2010)

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 (Dec 28, 2010)

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


----------



## syphlix (Jan 2, 2011)

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 (Jan 2, 2011)

syphlix said:


> 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 (Jan 2, 2011)

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


----------



## Garbz (Jan 2, 2011)

gryphonslair99 said:


> 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 (Jan 2, 2011)

Garbz said:


> gryphonslair99 said:
> 
> 
> > Crop factor has nothing to do with it.
> ...



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 (Jan 4, 2011)

clanthar said:


> syphlix said:
> 
> 
> > 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...
> ...



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 (Jan 5, 2011)

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.


----------



## Garbz (Jan 5, 2011)

gryphonslair99 said:


> Mixing apples and oranges only get us an fruit salad.  :mrgreen:



Depends on what you consider apples and oranges. I would definitely consider switching a 50mm lens for a 300mm lens and leaving all other things equal a completely different picture, whereas switching the 50mm for a 300mm and compensating by moving further away much more true to the original intent. 

Or to think about it this way, did I completely give up using my 50mm on my APS-C because it's now too long for 3/4 length portraits? Heck no, I just started standing further away from my subject to take the photo.


----------



## Dao (Jan 5, 2011)

Here something to think about.

Case: Take a photo of a coffee mug sitting on a kitchen counter.
Photo1: 100mm lens on 1.6x crop body compose -> shoot -> photo resize
Photo2: 100mm lens on full frame compose -> shoot -> crop the photo -> photo resize.
Photo3: 100mm lens on full frame walk closer compose -> shoot -> photo resize.

Assuming at the end, the size of the coffee mug on all 3 photos are the same and composition are some what the same. And final photo size are the same.

As far as perspective distortion concern, photo1 and photo2 should be the same, but not photo3.



So I believe the effect of 1.6x sensor on lens compression.  Technical, no effect.  However, if the camera to subject distance change due to image composition as a result of crop factor, you may say yes.  But really, that is not because of the lens, it is the photographer.


----------



## clanthar (Jan 5, 2011)

syphlix said:


> clanthar said:
> 
> 
> > syphlix said:
> ...



yes I think you may be misunderstanding and you are wrong.

Here's the error:

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

Yes the objects will look further away but they *will not* look further apart.

You are correct in your second assertion which is what I said; moving the camera will alter perspective.

stick you camera on a tripod with a 100mm lens on it and photograph a scene with a sign in it.

don't move the camera but switch to a 24mm lens and take another photo and compare the two.

The photo taken with the 24mm lens will have more content and if you made 8x10 prints of both photos everything in the photo from the 24mm lens will be smaller. HOWEVER the relative size and spatial relationship between objects in the two photos will be identical. Print each photo so the sign is the same print size in both and the photo from the 100mm lens will be an exact match to the center section of the photo from the 24mm lens.

The only way to change perspective is to move the camera -- with a stationary camera changing lenses only crops the content.

Joe


----------



## clanthar (Jan 5, 2011)

Garbz said:


> gryphonslair99 said:
> 
> 
> > Crop factor has nothing to do with it.
> ...



If you step further away from the subject then you are not trying to get the same picture. It's not the same picture if the perspective is altered. If you're trying to get the same picture you'll put the two different format cameras in the same place. Then use lens focal length (eg. normal lens on both) to keep the content the same. 

Joe


----------



## Hardrock (Jan 5, 2011)

Is this the compression you are talking about. Look half way down at the 2 water bottles. That is focal length compression (at least to me). The camera is obviously not in the same spot but the pink water bottle is very close to the same size in all three. Hope this helps.


----------



## djacobox372 (Jan 6, 2011)

The physical placement of the camera in relation to the subject is the ONLY thing that affects "compression." Focal length and sensor size has absolutely nothing to do with it! 

This is a fact, and not debatable. EOT


----------

