If I zoom in 2x in my photo is that the same as having twice as long of a lens?

Question

If I don't have access to a 200mm lens but I have a rather high resolution camera.

Does that mean if I zoom in 2x in my photo and half the mega pixel, I can achieve the same reach with a 100mm lens? Would the depth of field (DoF) be the same also (assuming both 2.8f)?

If you zoom in 2X you'll quarter (1/4) the megapixels. You'll halve both the width and the height. — Michael C, Feb 02 '22 at 07:24
This is really two separate questions, both have been well addressed here. For DoF when cropping (by either using a smaller sensor or cropping the result from the same large sensor, there's no real difference): Can a smaller sensor's "crop factor" be used to calculate the exact increase in depth of field? — Michael C, Feb 02 '22 at 08:28
For why cropping isn't the same as having a longer lens (with the same resolution limits), please see: Why is FF sharper than crop body for the same framing of the same object? and Relative performance of single lens on different format sensors (remember, cropping is no different than using a smaller sensor) and Will cropping an FX image to DX size have the same end detail for sensors with the same MP? — Michael C, Feb 02 '22 at 08:37
Also related: Does my crop sensor camera actually turn my lenses into a longer focal length? and What is crop factor and how does it relate to focal length? — Michael C, Feb 02 '22 at 08:39

rackandboneman · Answer 1 · 2022-02-02T16:29:38.463

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If there is some dedicated "advanced" zoom in your camera - eg Sony "ClearImage", NOT plain "digital zoom" - try using it and see if you like the results.

...

Note that focal length to crop equivalences are ONLY valid when the crop is from the center of the image (optical center of the lens used is in the center of the crop) OR for dead flat subject matter. Anything else will give subtle to gross perspective differences.

edited Feb 02 '22 at 16:29

answered Feb 02 '22 at 07:09

rackandboneman

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Perspective differences are a result of changes in camera position. Period. If the optical center (i.e. the "no parallex point") of each respective lens is in the same, the perspective will be identical. Geometric distortions due to the differences in lens projection are NOT perspective differences, they're differences in lens projection and/or in magnification variability across the field (that is, the focal length in the center of the field is slightly different that the focal length on the edge or corner). But those have nothing to do with perspective. – Michael C Feb 02 '22 at 07:20
Please see: What is the difference between perspective distortion and barrel or pincushion distortion? – Michael C Feb 02 '22 at 07:28
@MichaelC "no parallax point" == "crop from the center"? ...edited to clarify. But yes, I assumed a question asking about "half the mega pixel" (sic) can and should be answered in an informal way (perspective as anything that makes things unstraight in the picture) :) – rackandboneman Feb 02 '22 at 16:28
"makes things unstraight in the picture." That's not perspective, that's lens projection and geometric distortion. Those have nothing to do with the relative positions of the camera and the subject(s), and the relative position of various objects in the scene, which is what perspective is about. – Michael C Feb 05 '22 at 03:26

If I zoom in 2x in my photo is that the same as having twice as long of a lens?

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