Hi, I'm Tony Northrup, and for my Photography Buying Guide
I'd like to answer the very common question,
"Should you use full frame lenses on your crop bodies?"
And usually this comes about because somebody says,
"hey, you should always invest in glass before buying a new body."
And that advice sounds pretty wise, right?
It even sounds a little counter-intuitive, because a new body is so exciting.
But what this advice often leads to is people using
expensive full-frame lenses on their crop bodies.
And you're not quite getting what you might expect out of it.
So let's explore it a little bit and look at some real measurements
from DxOMark to see exactly what we are getting when we use these combinations.
We'll find scenarios where it does make sense, and maybe where it doesn't make sense.
First, I want to make the point that if you want to determine how a lens is going to behave
on a crop sensor body, on an APSC body,
you need to multiply both the aperture and the focal length
by the crop factor.
Many people only multiply the focal length by the crop factor and that tells you the field of view,
but it overstates the capabilities of the lens.
if you forget to multiply the crop factor by the aperture as well.
Here's an example:
I should point out the bottom here URL, sdp.io/crop
where I demonstrate exactly how this works. There are actually three parts to that video series.
If you really want to get into it, but the first video kind of demonstrates it hands-on.
Take a full-frame 24-70 f/2.8 lens:
this is one of the most common lenses I see people using on crop bodies.
If you put it on a Nikon or Sony APSC body with a 1.5x crop,
it behaves exactly like a 36-105mm f/4.2 full-frame lens would
on a full frame body.
So, you don't get either the depth of field, the total light gathered, or the same angle of view
you have to change all of those things. It becomes a very different lens.
and I'd like to make the point that the focal length probably isn't as useful.
I love using 24mm at the wide end, that's kind of what you need if you're shooting a gathering,
if you're with your friends, if you're out, if you're shooting an event.
36mm is pretty tight for that and you're going to find yourself backing up a lot.
So you might find that the adjusted focal lengths themselves aren't that useful.
Now if you have a Canon lens, a Canon body,
the APSC sensor's a little smaller, you have to multiply it times 1.6,
so it become a little more telephoto and that aperture actually becomes a higher f/stop number, effectively.
Another common lens I see people using is the 70-200 f/2.8. People use it as a portrait and sports lens.
It becomes basically a 100-300 f/4.2 on Nikon and Sony, or 112-320 f/4.5 on Canon bodies.
Now, let's answer the question, are full frame lenses sharper on crop bodies?
This comes up because, people notice that the centers of lenses tend to be sharper than the edges.
The edges tend to get a little less sharp.
So they logic that by using a crop sensor, which uses just the center part of the image circle coming from the lens,
that the image itself must be sharper.
We can test this, and know definitively looking at DxO Mark numbers.
And I'll show you how to check the sharpness according to DxO Mark in just a bit.
Let's take a look at the Canon 5D Mark III versus the 7D
both with the original 24-70 f/2.8.
And, I'll tell you why I'm using this particular example.
Because I have a friend who's a genius, and he heard that advice about crop bodies being sharper
with full frame lenses, and invested in a very expensive 24-70 f/2.8
and he sent it to Canon twice for repairs, because he said he just wasn't getting sharp results.
And this is why! The lens was functioning fine.
On a 5D Mark III it would have given him 14 perceptual megapixels, that's basically how much detail you can see.
And on a Canon 7D which he was using, it only gives you 7 perceptual megapixels. 7 megapixels!
So that's not sharp at all. In fact,
he could have gotten better results if he had just used the kit lens. The 18-35 mm
kit lens, which costs about $200,
would've given him about 8 perceptual megapixels.
That fancy 24-70 which costs $1,500, this was the original Mark I,
only gave him 7 megapixels. At 7 1/2 times the price!
So this is why it's really important. Because I see people all the time laying out thousands of extra dollars,
and then they're being frustrated because they're not getting sharp results.
And this is one of the big causes, just be aware of that.
Lenses designed for smaller sensors will give you sharper results
because they're focusing all that light that's coming into the lens onto the sensor itself.
When you crop like that you're also losing detail.
It's like doing a digital zoom, basically.
Let's take a look at another example:
This is the newer 24-70 f/2.8, which is a sharper lens, on the Canon 7D.
It becomes a 38-112 f/4.5 with 11 perceptual megapixels, that's doing pretty good
on an 18 megapixel sensor.
And, if on the other hand, you were to use Sigma's 18-35 f/1.8
you would have gotten 13 perceptual megapixels at between half and 1/3 the price.
So a much, much cheaper lens at $800 instead of $2,100
and you're getting sharper results.
That Sigma 18-35 f/1.8, i'll give you a link for it in a bit,
is a fantastic lens and it's designed for APSC cameras,
that's why. You're not abusing it.
it's also giving you a more useful focal length, by being 29-56 instead of 38-112.
Now, the zoom distance itself isn't as much, it's one of the drawbacks of that lens, but
if you want sharpness, that's the way to go on an APSC body.
Now let's take a look in the Nikon world, at a very similar comparison here.
The D610 which has a 24 megapixel full-frame sensor,
with the Nikon 24-120 f/4, that will give you about 13 perceptual megapixels,
that's not a very sharp lens, I recommend the Sigma 24-105 instead, I have that right there.
If you match that up instead with the D7100, also has 24 megapixels but with a 1.5x crop,
the whole set-up ends up being only 9 perceptual megapixels.
So you can see you have a substantial drop, almost 50 percent fewer perceived megapixels,
50% less detai- or a third less, detail, in the D7100 with that same lens.
Because it's designed for full-frame. And you're just losing all that light that's coming in.
You're not getting the most out of the lens.
Let's compare a full-frame set up, the D610 and Nikon 24-70, to an APSC set up,
The D3300 and Sigma 18-35 f/1.8.
They both gather about the same total light,
so in a given environment you could expect them to have the same amount of noise.
The D3300 with the Sigma has a little less zoom range.
The full-frame camera's producing only 15 megapixels of detail
and the APSC camera's producing 17 megapixels of detail.
Here, because we've carefully matched the lens to the body,
we chose an APSC lens for an APSC body,
we actually managed to beat the full-frame set-up that costs more than twice as much.
So are full frame lenses sharper on crop bodies?
No, definitely not, looking at the numbers, it definitely seems like that's not the case.
Which pro APS-C lens should I buy? And I've mentioned it a couple times, but the Sigma 18-35 f/1.8.
There's a link to it there, and I want to be clear,
I'll get a few pennies if you happen to use my link, and I appreciate the support, but I don't have any relationship to Sigma.
They've never paid me and I've never accepted any free gear, nor have I from any camera or hardware manufacturer.
I just happen to love that lens.
Another question: should you use crop bodies for wildlife?
Crop bodies have a higher pixel density, and therefore they can extract more detail
out of the amount of detail that the lens is capable of producing
if you have to crop anyway. So,
the reason this is a wildlife scenario instead of a portrait scenario is
with portraits you can just get closer to your subject and fill the frame.
But with wildlife you often cannot fill the frame.
So if you're shooting wildlife and you find that you're often cropping with your full frame body,
you might get better and sharper results by connecting a crop body to that
full frame glass. This is an exception to the rule we just discovered about sharpness.
So, how do you calculate megapixels when cropping a sensor? A question I want to address first.
Many people do this incorrectly. The correct formula is:
the total number of megapixels divided by the crop factor squared.
So if you have a 1.5x crop factor, you square that,
so 1.5 times 1.5 is 2.25,
and then it's the number of megapixels, like 24, divided by 2.25.
We'll look at a couple of examples.
The D810 has a 36 megapixel sensor,
if you put it into it's 1.5x crop mode, it produces 16 megapixel images.
So by contrast, the D7100, which is an APS-C body and natively 1.5x, is 24 megapixels.
So the D810 has 36 megapixels, and the D7100 only has 24 megapixels.
But if you have to crop to 1.5x anyway, because you're too far from the subject,
then the D7100 is actually going to give you substantially more detail.
50% more detail.
And that's a really big difference that you will notice in your pictures.
The 5D Mark III is 22 mexapixels
if you have to crop 1.6x anyway, the final image is only going to be
8.6 megapixels. Now if you use the new 7D Mark II, which we absolutely love,
you're going to be getting 20 megapixels in that same image area.
So when you can't get close to your subject, when you have to crop,
you can use a lot more megapixels by using an APS-C body, because the pixels are just crammed into a smaller space.
taking up just the center part of the lens. Basically they're cropping for you.
Now I'm just talking numbers here, but I back all this up with real world experimentation.
I often switch between the 5D Mark III when I can get close enough to birds,
and the 7D, or more recently the 7D Mark II,
and when I've shot them side by side, you see more detail out of the 7D Mark II.
Most definitely, in scenarios where you have to crop.
It's always better to get close to the animals, but we know,
if you shoot wildlife you know you can't always do that.
Let's look at some actual real world measurements here from DxOMark.
The Nikon 400mm f/2.8, and amazing lens, about the sharpest in the world,
with the D810, produces 33 megapixels of detail,
which is remarkable, considering it's a 36 megapixel lens. It almost never gets that close to the theoretical physical limit.
But if you have to crop it 1.5x times, that means it's going to be about 15 perceptual megapixels of detail in your picture. So,
if you're shooting wildlife and you have to crop, that's what you'd get.
If you were to attach that same lens to a D610, you'd get
only 10 megapixels out of that cropped image.
But if you put it on a D7100 body, you'd get 17 megapixels out of it.
So here we see the D7100, a much cheaper body,
keeps up pretty well with the D810 despite it's smaller megapixel count.
And it completely surpasses the more expensive D610, providing 70% more detail.
In the Canon world, we can see with the mighty big 600mm f/4,
the 5D Mark III will produce about 20 megapixels of detail, if you can fill the frame.
But if you're cropping 1.6 times anyway?
It's only gonna give you about 8 perceptual megapixels of detail.
The mighty 1DX, the $6500 top-end camera, is only going to produce about 7 megapixels of detail with that lens.
Put it on the cheapo 70D, Canon's mid-range APS-C body,
and you'll get 14 megapixels of detail.
So yes, in wildlife scenarios where you have to crop,
you'll get twice as much detail out of a much cheaper 70D,
what do they cost, 6- or 700 bucks? Compared to the 1DX which costs like $6000.
So these are the kind of decisions that can make a big impact on your photography
or your wallet, depending on which way you go.
So do crop bodies give more detail when you have to crop anyway?
Yes, most definitely.
Should you use full frame lenses on crop bodies? Only for wildlife.
Is kind of what we're determining by looking at these numbers.
Whenever possible, for regular day-to-day shooting when you can control the distance to the subject and fill the frame,
APS-C lenses on APS-C bodies
and if you just want the quality of the higher end lenses, you should probably go ahead and upgrade your body too.
Sell your old gear and upgrade everything to full frame, or just stick with the APS-C lenses.
But if you're doing wildlife, put your money into that big lens
and use the best APS-C body that you can.
So, how can you check the sharpness of your lens and body combination?
And I'll jump into the browser here and just go to Google real quick.
And what I usually do is search for DxOMark, just the name like that,
and then the name of the lens. So let's check the Canon 100-400.
And usually the first result is fine, so I'll just click that blindly and
and what comes up is this lens and then there's a drop list here to tell you which camera that they've tested it with
so let's check out the 5D Mark III, one of my favorite full frame bodies.
And we'll see that it's giving us 13 perceptual megapixels of detail.
We could also switch to the 6D
and that only gives us 12 megapixels of detail.
They have just about every major camera and lens in there, but I suggest searching for the lens first and then selecting your body from the list.
Just to summarize it: use APS-C lenses with APS-C bodies for sharpest results.
Use full frame lenses on APS-C bodies with wildlife for sharpest results.
And of course if you want more information check my Photography Buying Guide
which explores cameras, lenses, flashes, studio lighting, tripods, computer equipment
and just about everything else you could imagine hardware-wise in great amounts of detail.
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