Is the foreground-background perspective strictly a function of the focal length of a lens or is it a function of focal length and crop factor? In other words, if I put a 85mm f/1.2 on a full frame camera will I see the same subtle compression on a 1.3 crop factor camera as on the full frame, or will it be more like that of a 110 mm lens?
I'm thinking that shift in perspective is the same whether the sensor is full frame or cropped, but Lord knows I've been wrong before.
Well, from my point of view. With a 'box' camera, ie one without movements, perspective is determined by where the camera is placed - well maybe more precisely where the nodal point of the lens is (as I've learned by doing a bit of panoramic stiching). So, perspective does not change when my 35 mm camera is mounted on a tripod and I zoom through the focal lengths of a lens. You can demonstrate this by carefully aligning a near object with a far object, then zooming. You can also demonstrate it with a wide angle shot and a pair of scissors. People argue with this. The specious concepts of telephoto perspective and wide angle perspective run deep and strong (or is that shallow and wide?) in our photographic folklore.
A camera (or lens) with movements is different. I'm not familiar with either of those.
The lens sees the eact same image regardless of sensor size. The varying sized sensors simply record more or less of that image. It's like placing a mat over a photo. The photo is still the same, you just see less of it. The illusion is that you have "zoomed in" because you see less of the scene with the same lens.
Perspective is the same but you lose the additional perspective (especially with wide lenses) you would get at the edges because the reduced size sensor doesn't record it.
The compression effect is a result of magnification (which is a function of focal length). The sensor size has no effect on magnification. The easiest way to visualize it is imagine light going through the lens and being projected as a circle on the other side. The cropped sensor simply covers a smaller part of that circle but has no influence on any optical effects.
Perspective is a matter of position ONLY. Cropping doesn't matter, and neither does focal length. The image from a cropped camera will be exactly the same as the middle part of the image from a full-frame camera. The image from a camera with a telephoto lens will be exactly the same as the centre part of the image from a camera with a wide angle lens. Magnification is affected, but perspective is NOT.
Perspective changes when you change positions. If you move your cropped camera back to get the same magnification, with the same lens, as a full frame camera, perspective will change, because the position has changed.
-Paul
Posted by Mike Maples on June 20, 2006 at 10:52 AM
My comment about perspective may have been misleading. Let me attempt to clarify.
What I was trying to convey was the perspective can appear to change with different crop factors especially with wide lenses. When shooting with a very wide lens you get a fisheye effect that is more pronounced as you reach the edges of the captured image. If you crop the edges enough it gives the appearance of a change of perspective even though the remaining portion of the image is exactly the same as it always was. To achieve the same overall "look" with a 1.5 crop camera would require a wider lens. The cropped image would "appear" to have a change in perspective if you viewed identical size prints made with a full frame camera and a crop factor camera side by side.
It all makes sense now (thanks for the link Pete). Let me see if I can state what I think I've learned. If you remain stationary the foreground/background compression is constant regardless of the focal length of the lens. You will just have a larger or smaller image of the same perspective. If you alter focal lengths and zoom with your feet to keep one element in the scene a constant size, the foreground/background compression will change; flatten with a longer lens and deepen with a shorter lens.
Kelly, Don't tempt me back into this quagmire, but yes, what you wrote is true. It is obvious now, but I was delighted to realize that I could move objects, relative to each other, by moving my lazy... feet. Three dimensional composition is 1.5 times more fun than framing.
Pete D.
Discussion
10 repliesI'm thinking that shift in perspective is the same whether the sensor is full frame or cropped, but Lord knows I've been wrong before.
A camera (or lens) with movements is different. I'm not familiar with either of those.
Pete D.
Perspective is the same but you lose the additional perspective (especially with wide lenses) you would get at the edges because the reduced size sensor doesn't record it.
Hope that made sense.
Guy
http://www.vanwalree.com/optics/misconceptions.html
Perspective changes when you change positions. If you move your cropped camera back to get the same magnification, with the same lens, as a full frame camera, perspective will change, because the position has changed.
-Paul
What I was trying to convey was the perspective can appear to change with different crop factors especially with wide lenses. When shooting with a very wide lens you get a fisheye effect that is more pronounced as you reach the edges of the captured image. If you crop the edges enough it gives the appearance of a change of perspective even though the remaining portion of the image is exactly the same as it always was. To achieve the same overall "look" with a 1.5 crop camera would require a wider lens. The cropped image would "appear" to have a change in perspective if you viewed identical size prints made with a full frame camera and a crop factor camera side by side.
Bingo! You have to change the location of the camera relative to the subject to change "perspective."
Pete D.