Today, I want to make a quick video
clearing up some issues
with those ubiquitous crop factor illustrations
you see all over Google and YouTube,
like this one and this one,
which are only relevant in a small fraction of use cases,
and I think might be causing some users
to draw inaccurate conclusions about what is actually
going on inside of their crop factor cameras.
Let's get Undone.
[offbeat music]
♪ Gerald Undone ♪
♪ He's crazy ♪
What is happening, everybody? I'm Gerald Undone,
and today we're talking crop factor.
Now I know many of you probably already have
a decent understanding of crop factor,
so I'm just gonna give a very brief recap,
and then we're going to move right into the illustrations
and what I kind of find a bit wonky about them.
But for a basic quickfire explanation,
crop factor is that thing of how an image
looks a certain way on full-frame,
and then it looks tighter
when it's not on full-frame,
like when it's on APS-C or Micro Four Thirds,
and that's because of the-- you know,
multiplier of the field of view based on the sensor size,
and that multiplier is the crop factor.
In the case of APS-C, for instance,
it's 1.5x, so if you're looking through a lens
on a full-frame camera and it was a 35mm lens,
if you strap that lens on an APS-C camera
which has a 1.5x crop factor,
the lens would be--
it would look like a 50mm lens would look--
a 52.5mm, to be exact--
lens would look on a full-frame camera.
And if you put it on a Canon APS-C body,
which is EF-S, it's a 1.6x crop,
so it'd look more like a 56mm lens would,
full-frame equivalent.
And if it was on Micro Four Thirds,
which has a 2x crop,
the 35mm lens on a Micro Four Thirds body would have
a 70mm field of view equivalent to a full-frame lens.
Meaning you'd have to have a 70mm lens
on a full-frame camera to have the same field of view
as you would a 35mm lens on a Micro Four Thirds camera.
But a lot of you probably knew that already!
I just wanted to make sure that we had
that basic understanding for those that didn't know
for what we're about to talk about.
Now, when you look up "crop factor,"
look up "what's my crop factor of my camera"
and that kind of thing,
you're gonna see the same kind of illustration everywhere.
What is that illustration?
Well, it's putting boxes inside of boxes,
and this is done to give you sort of an idea
of what the different sensor sizes are,
and to, kind of, show you
what sort of details of an image
you would get with the different sensors.
Because obviously if you had a tighter field of view,
you'd only be able to see a certain amount
with this sensor size, and if you had this sensor size
you'd be able to see that amount.
Sometimes to get even fancier,
rather than using a rectangle, they use an image circle,
which makes a lot more sense, obviously,
because lenses are circular, so lenses obviously
aren't going to create a rectangular image.
But even the circular examples
still put the boxes inside of boxes.
Now, this illustration is handy
for having an idea of how much of an image of a given frame
will be "cropped away,"
and that's kind of where it got its name from,
because it almost looks as if sections
of the full-frame image are just being cropped away,
and what's left over is the smaller sensor size image.
And this is the reason why lens benchmarks
often show lower scores for quality full-frame glass
being used on an APS-C body
versus using native APS-C specifically designed glass,
because of all this extra image
that's just gonna be cropped away.
And this is my biggest issue with these illustrations,
is that it's not showing you anything
even close to what's going on when you put a lens
that was specifically designed for your smaller sensor camera
on, like if you put an APS-C lens on an APS-C body,
or Micro Four Thirds lens on a Micro Four Thirds body,
this isn't what's happening.
There's not all this extra real estate
that's being cropped away, and therefore,
they're not really "crop sensors" anymore,
and these illustrations don't really show that.
Now, there's a slightly more accurate illustration
that you'll see from time to time that shows a side view
and incorporates a lens, and it has a subject,
and it shows you the angle of view,
and it shows you how much of the subject
will be visible on the full-frame sensor.
And then they'll overlay an APS-C sensor
and you'll see a narrower field of view,
and you'll see that the subject
is being restricted a little bit at how much will be seen,
and then you'll be able to get a guess over here
as to how much of the subject will be "cropped."
But again, without eliminating the full-frame image circle,
while better, this illustration
still fails to show accurately what's happening
when we put a lens on designed specifically
for a smaller sensor.
So I'm gonna try and demonstrate what actually
happens inside the camera using this image
that you're seeing of me here now--
which was shot, by the way,
on a Micro Four Thirds camera with a lens
designed for a Micro Four Thirds camera.
And I'm gonna try and demonstrate that
using this image here.
Now, for the sake of this illustration,
the boxes that I'm gonna use are gonna be 16:9 aspect ratio,
because they'll fit better inside this 16:9 video frame.
But if we're talking about real sensors here,
they'd most likely be a 3:2 aspect ratio,
like a full-frame sensor, 36x24.
That's a 3:2.
But it shouldn't really make a difference
for this explanation that we're using 16:9.
I'm also gonna keep my explanation of the lens
extremely rudimentary to avoid
any complicated discussion on optics,
because I think that would be counterproductive
to this mental exercise.
For this illustration, I just need one more thing,
-which is my flashlight which-- -[ding]
...is on that back shelf right now,
so just give me one second to grab that,
and then we'll carry on with this illustration.
[grunting]
Almost there...
Ugh...got it!
[grunting]
[sighs]
OK. Now imagine that our subject is over there,
and this is the lens, and we're shooting this way, OK?
And then this is the sensor on the back.
The subject's there.
What a lens designed specifically for
a smaller sensor will do is create a smaller image circle.
So if you see the light on my hand as being the image circle
that's projected, if you will, onto the sensor,
the smaller lenses will actually create
a smaller image circle.
Now, if the sensor was smaller on my hand,
as you can see, this would fit perfectly.
But if we use a bigger full-frame lens,
it creates a large image circle like this, and as you can see,
less light is actually hitting the center of my hand now,
because it's spread out more into a larger circle.
And this is wasteful, because a lot of the image
is gonna be cut away, and we're not concentrating
the image well onto the sensor.
That's why we use lenses
specifically designed for the sensors.
Basically, if you were projecting a show
and you wanted to put on the best show you possibly could,
you would want the projector to project only the size
that would perfectly fit the screen
that you were watching it on,
and you would want to accomplish this over
the shortest distance you could in order to preserve
as much of the light concentration as possible.
So rather than this illustration,
which you regularly see, which shows a full-frame lens
on a Micro Four Thirds body and would require cropping
in order to finish the frame, a Micro Four Thirds lens
looks like this and requires no cropping at all.
But if you were to stick that Micro Four Thirds lens
onto a full-frame body, it would look like this,
because the Micro Four Thirds lens
is projecting a smaller image circle onto a screen
big enough to be able to see the limits of it.
And this is how speed boosters work.
So let's go back to the full-frame lens
on the Micro Four Thirds body demonstration,
and we'll talk about speed boosters,
like the ones that you can get from Metabones.
Now, what they do is they take this overly large image circle
that you get from full-frame glass
on a Micro Four Thirds body,
and they use an additional lens element
to refocus it down to fit the smaller sensor size.
It's just like turning one of those knobs
on a light that goes from a floodlight
to a spotlight and puts more light concentration.
In this case, it's increasing the total amount
of light hitting the sensor,
which of course lets you have a faster exposure,
thus, "speed booster."
So as you can see, none of this involves "cropping,"
and that's my main issue
with those common illustrations,
is that they only really apply to
when you're putting a full-frame lens
onto a smaller-sensored body without using a speed booster.
And then, yeah, sure, then you'd have boxes in boxes,
and the smaller sensor would have a smaller grab
of that bigger image circle,
and so then you can use it to have an understanding
of "how much of the mountain
you'll see on a Micro Four Thirds,
then you'll see more of the mountain on a APS-C."
But really, that's not what's happening.
It's field of view that's being determined
physically by the lens.
This is a perfect time to talk about
another misconception when it comes to lenses,
which is that the focal length is somehow changing
when you switch bodies. It's not.
If you have a 35mm lens for a full-frame camera,
and over here you got a 35mm lens
for a Micro Four Thirds camera, they're both 35mm lenses.
And if you switch 'em up on all the different bodies,
they're still 35mm lenses,
because that focal length is a physical construct
that doesn't change
just because of which body you put on.
It's a measurable distance inside
that makes the lens that focal length, 35mm,
and it's-- it's just always going to be that.
Now, what does change, though, is the angle of view,
or the field of view.
And if you look up on a website
when you're trying to buy a lens,
you can see "35mm," but then below,
you'll see the angle of view or the field of view.
And a full-frame lens
will always have a wider field of view
than a smaller-sensored lens will.
Like, if you buy an EF-S lens from Canon,
it's gonna be narrower than their EF version would be.
That's just the way that it goes.
And that's because that larger angle of view
is necessary when you're reciprocating it
and projecting it on to your sensor,
because the sensor is larger,
so you need to be able to project it wider as well.
And that's great, except for when you put that
onto a smaller sensor,
then you have too much angle of view,
and all that extra stuff is gonna be cropped away,
which is why, often, you'll have a lower total sharpness
when using a great high-quality full-frame lens
on a smaller-sensored body,
unless you're using a speed booster.
Anyway, that's gonna be it for me. I hope you found
this video helpful, or at least entertaining.
And if you did, make sure you leave it the old thumbs-up.
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Alright! I'm done.