Will stepping back and using an FX lens on a DX body get the same "look" as the same lens on an FX body?

Question

Using 85mm as an example, how can I get the same "85mm look" (shot on a FX camera with an 85mm FX lens) on a DX camera with the same 85mm FX lens??

I know a 58mm FX lens (87mm DX equiv), shot from the exact same distance with a DX camera, will look almost identical and yield a very close perspective background.

But is the only other way to get the same "85mm look" on a DX camera, with an 85mm FX lens, to simply move backwards?

Will this simple technique give me the same non-cropped image a FX camera would have produced with the 85mm FX lens?

I understand that from the same distance the DX camera will produce a larger image like a 127mm. If I simply move back a few feet will my photo look like a perfect 85mm photo an FX camera would have produced with the FX lens at the shorter distance?

I know the bokeh, perspective and composition will be slightly different but do you essentially get the exact same "mm look" with a FX lens on a DX body by simply moving back a few feet?

Of course, with a wide-angle lens, other things are going on but for basically a full body shot of a person does simply moving back a few feet turn a 85mm FX lens into a perfect 85mm lens for a DX camera? Or do you lose that "85mm look" by putting more distance between you and the subject?

Answer 1

No. You can only get the same look by standing in the same place. Otherwise, perspective will be altered. Nothing you can do with the lens (or camera) can get around that.

On a DX format camera, to get an "85mm look" — the look of an 85mm lens on a "full frame" 35mm-format camera, or FX in Nikon terms — you need a lens that's 1.5× shorter to match field of view, and also approximately with an aperture 1.5× faster to get the same approximate depth of field.

You can also use the "Brenizer method" of panoramic stitching to simulate a wider and faster lens than you have, but you'll still have to stand in the same place to get the same look.

So:

I know a 58mm FX lens (87mm DX equiv), shot from the exact same distance with a DX camera, will look almost identical and yield a very close perspective background.

Yeah.

But is the only other way to get the same "85mm look" on a DX camera, with an 85mm FX lens, to simply move backwards?

Nope. This will give you something like a "135mm look" (give or take), because that's what you'd use on FX to get the same framing from that spot.

Take a look at some of the graphics in the answers to What does it really mean that telephoto lenses "flatten" scenes? — I think they'll really help.

Answer 2

“Correct” perspective is not critical for most images. Portraiture is an exception. Things close to the camera reproduce large and things far from the camera reproduce small. If the camera is worked in too close, the nose reproduces too large and the ears too small. This is the dreaded facial distortion that makes portraits look weird.

Factorial: An image will display correct perspective if viewed from a distance about equal to the focal length multiplied by the magnification used to make the displayed image.

Say we make a portrait imaged with our FX camera. The frame size is 24mm X 36mm. This is a miniature image that must be enlarged to be viewed and scrutinized. We make an 8 X 12 inch image and display it. To make the 8 X 12 we were required to magnify (enlarge), the FX frame 8.5X.

We mount an 85mm. lens to do this task. The viewing distance for correct perspective becomes 85mm X 8.5 (magnification) = 723mm (28 inches). In other words, a portrait taken using an FX camera with an 85mm lens is enlarged to make an 8 X 12 inch print is suitable for viewing and the viewing distance becomes 723mm (28.4 inches). This image presents “correct” perspective.

Now we mount the 85mm on an FX. The frame size is 16mm X 24mm. To make the same 8 x 12 inch print we must enlarge this miniature frame 12.7 X. This magnification is 1.5 X greater than used to make the same image with the DX camera. With this lash-up the viewing distance becomes 85mm X 12.7 (magnification) = 1080mm (42 ½ inches). If this image is viewed from about 42 inches, the image displays correct perspective.

If we choose to view the 8 X 12 image made with the FX from 28 inches, the same as the image made using the DX, we must mount a shorter lens to achieve “correct” perspective.

The math is 85 ÷ 1.5 = 60mm (rounded). We mount a 60mm and make the portrait. The displayed print is viewed from 60mmn x 12.7 (magnification) = 762mm (30 inches).

Bottom line, when we a mount an 85mm on the FX and a 60mm on the DX, we can make a displayed images that when viewed from the same distance (about 30 inches) display similar perspective.

Addendum:

We choose the subject to camera distance to obtain a desired linear perspective. In portraiture correct linear perspective is the major contributor when it comes to pleasing the client. Fist we select the camera position then we select the focal length. Subject distance defines the perspective. Next we select a focal length. Focal length defines the how the principle subject is positioned within the frame. Short focal lengths reduce the size of the principle subject at the price of including more of the surroundings. Longer focal lengths enlarge the principle subject thus excluding the surroundings.

Linear perspective is a function of camera to subject distance. The liner perspective remains the same regardless of focal length or format size. The answer is: If the camera position is not changed, the perspective perceived is the same regardless of focal length or camera format.