This Video Explains the Misconceptions Surrounding Crop Factor Equivalency

If you want to understand the basic principles of crop factor, depth of field, and sensor size, then you should check out this video.

If you really like to nerd out over gear, then this is your moment. Blake Evans tackles the myths, misconceptions, and general confusion surrounding depth of field, crop factor, and the differences between full frame and crop sensors. In this very detailed video, as well as in his equally detailed write-up in PetaPixel, he offers illustrations that explain these principles in depth to show you what you need in order to get a true equivalent image from different sized sensors.

As you might've noticed, this video isn't for the faint of heart. It's geared toward professionals who not only have some advanced knowledge of crop factor and camera sensors, but who also want to fully understand crop factor equivalence, as well as how speed boosters work.

As Evans explains, the "recipe" for crop factor equivalence is pretty straightforward; it's the reasons why you need to use it that some have a hard time understanding. The idea here is that it's not just about getting the same field of view or exposure between different sensor sizes, it's also about getting true equivalence: same lens, aperture, distance, depth of field, everything. To do this, you should not only be applying your crop factor to your lens' focal length, but to your aperture and ISO as well. When you do it right, not only will your field of view and depth of field be equal, but your noise levels will be, too.

Evans' recipe for crop factor equivalence
Evans shares some examples of what it looks like when you achieve full crop factor equivalence:

Notice how the "bokeh balls" on the car are the same size.
Evans gets extremely detailed in his video, so I highly suggest watching 36 minutes of it to get a better understanding of what he's saying. Though he's talking about pretty meaty, complicated stuff, he does an excellent job explaining it clearly.     

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6 Comments

Thank you so much. Much detailed video.
(Reminds me about my physics class)

March 30, 2017 at 12:49AM

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Sameir Ali
Director of Photography
1411

One of the better video explanations out there.

In the end, a M43 can achieve the same results as a FF, as long as you adjust your settings and distance, which almost everyone knows. You hope=) You need faster lenses to create more bokeh, but when some people say one sensor is "better", they don't quite understand the math. Easier to achieve "X,Y,Z" is more appropriate.

Since nearly all video cameras are S35 anyway, we're not talking a massive stretch to achieve FF, especially when you're using speed boosters. Our FS5/FS7 with Canon Lenses are basically full frame. For grins, I've brought along my personal GH4 with a 25mm prime on a couple of shoots and have easily matched them, bokeh for bokeh, DOF for DOF, with little effort. Had to open it up a bit more, but no one would ever guess which camera is which.

March 30, 2017 at 5:36AM

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Josh.R
Motion Designer/Predator
1049

This is great! Thank you.

March 30, 2017 at 6:13AM

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Josef Lorenzo
Director
400

Excellent video. One possible correction: When showing the out of focus green dot on the apple that was further away than the in focus red dot, the drawing shows that dot coming into focus behind the film plane. I think this is backwards. I'm imagining taking that picture with a view camera and if I want to focus on something closer I pull the film plane further from the lens. If I want to focus on something further away I push the film plane closer to the lens. I use a view camera as the example because its easier for me to imagine the lens/subject relationship remaining fixed while the film plane moves. With a single lens reflex usually the camera stays fixed while the lens moves in and out so not as clear an illustration...

March 30, 2017 at 2:49PM, Edited March 30, 3:21PM

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Brad Slade
Photographer
102

Also, I've wondered if the engineering problems are any harder to make a 35 f1 lens for super 35 (rough guess, not doing the math) than a 50 f1.4 for ff. I've always been surprised there aren't more fast primes out there for "cropped" sensor cameras.

March 30, 2017 at 3:02PM, Edited March 30, 3:23PM

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Brad Slade
Photographer
102

When I step upon one of these videos that "finnaly explain to you dumb people how depth of field really works", I rush to the part comparing big (S35, FF) sensors to small (M43) sensors.
And again, the author tries to "prove" that our eyes cannot be trusted, because "a small sensor has actually shalower dof than a large sensor" (his words, exactly)
In order to "prove" that, he shows frame grabs, from different size sensors, of the same scene... with a bigger (2 stops bigger) aperture on the M43s sensor.
Like if adjusting your aperture to the equivalent of FOUR TIMES AS MUCH LIGHT on a scene "a minor, irrelevant difference".
Why not use to compare with the big sensor a painter with acrylics instead? Since anything goes to "prove" something obviously wrong in order to look smart...

November 5, 2017 at 5:26PM

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