Should I Use a Crop Sensor or Crop an Image From a Full Frame Sensor?

Should I Use a Crop Sensor or Crop an Image From a Full Frame Sensor?

If a crop sensor is used, it will look like the focal length is much longer. Photographers that need long telephoto lenses can benefit from this. But instead of using a crop sensor, it is also possible to crop a full frame sensor to have the same field of view. Let's take a look at the differences.

It isn’t really that difficult. A small sensor will record only a part of the projected image of the lens you are using. A bigger sensor will record a larger part of that same projected image. A full frame sensor with the dimensions of 24 x 36 mm will have a larger area compared to a 1.5x crop sensor that measures 23 x 15 mm. But when the recorded image is viewed at the same size on a screen, the image of the crop sensor will result in a magnification of 1.5 times that of the full frame sensor.

This is why a lens on a camera with a sensor that is smaller than a full frame sensor will act as if it has a longer focal length. A 24mm the lens will act like a 36mm lens, a 50mm lens will become a 75mm lens, and a 400mm lens will imitate a 600mm lens. This is when the sensor has a 1.5x crop. If a micro 4/3 sensor is used, with a crop factor of 2x, the focal lengths will be 50mm, 100mm, and 800mm compared to its full frame cousin.

A Canon 1,6x crop camera next to a Panasonic 2x crop camera (MFT).

A Canon 1.6x crop camera next to a Panasonic 2x crop camera (MFT).

Use Crop Sensors When You Need a Long Focal Length

If you need long lenses for your photography, a crop sensor seems to be ideal. Because of its smaller sensor, the lenses will appear to be much longer. There are even cameras, like the Nikon Coolpix P1000, with such small sensors that its lens will act like a 3,000mm full frame equivalent. Imagine what a 3,000mm lens on a full frame would look like.

The amazing Nikon Coolpix P1000 with a full frame equivalent lens of 3000mm

The amazing Nikon Coolpix P1000 with a full frame equivalent lens of 3,000mm

But let up ignore these superzooms with fixed lenses and look at the lens interchangeable cameras like the DSLR and its mirrorless siblings. On a 1.5x crop camera, a 400mm lens will act like a 600mm lens in a 400mm package. Put the lens on a 2x crop camera, like the micro 4/3, and it will be an 800mm lens in a 400mm package. It has a huge benefit due to its size and weight and how easily it can fit into a camera bag.

Using a 800mm lens on a full frame camera. It is not that easy to take with you.

Using a 800mm lens on a full frame camera. It is not that easy to take with you.

Crop a Full Frame Sensor to Imitate a Long Focal Length

Since a crop sensor only records a part of the projection circle, it is also possible to imitate this by cropping the image of a full frame sensor. You can end up with the same image as from a crop sensor. This way, we can enlarge our subject the same way compared to a crop sensor but in the post-processing part of the workflow.

You could shoot with a full frame and crop afterwards. You could also uise a crop camera. Which is the better choice?

You could shoot with a full frame and crop afterwards. You could also use a crop camera. Which is the better choice?

Here is the catch. When cropping a full frame image to have a larger magnification, we throw away resolution. We lose pixels. If you want to crop 1.5x to imitate the image from a smaller sensor, you lose between 30% and 40% percent of the resolution. With the high pixel counts of modern sensors, that doesn’t have to be a problem whatsoever. You still end up with enough pixels to make large prints, if necessary.

Is a Crop From a Full Frame Sensor Better Concerning Resolution or Not?

Most crop sensors have resolutions that are somewhere between 18 million and 24 million pixels. Full frame sensors have somewhere between 24 million and 30 million pixels. Newer cameras, both crop and full frame, can have even a higher resolution.

Let’s do a little math. I am going to compare a 20-megapixel Canon EOS 7D Mark II with a 30-megapixel Canon EOS 5D Mark IV as an example. For the Canon EOS 7D Mark II, the surface area is 336 square millimeters. The pixel density is 59,500 pixels per square millimeter. The Canon EOS 5D has a surface area of 864 square millimeters, resulting in a pixel density of 34,800 pixels per square millimeter.

I shot this flying cuckoo with a 100mm lens on a full frame camera, and used a heavy crop. Using a 100mm lens on a MFT camera would have the same result.

I shot this flying cuckoo with a 100mm lens on a full frame camera and used a heavy crop. Using a 100mm lens on a MFT camera would have the same result.

If we use a 400mm lens on both a Canon EOS 7D Mark II and a Canon EOS 5D Mark IV, and we crop the image of the latter, resulting in the same focal length or subject magnification if you will, the Canon EOS 7D Mark II has a much higher resolution. Therefore, the crop camera would record much more detail compared to the full frame camera with a post-processing crop.

What About Image Quality?

At first sight, you would think a photo from a crop sensor will show much more detail because of the higher pixel count. But there is a major downside to a lot of pixels per square millimeter. It can result in higher noise levels, especially when the ISO level is cranked up. A high noise level will result in a loss in detail. 

The noise levels of a Canon EOS 7D mark II at ISO6400. Due to the high noise levels some details are lost.

The noise levels of a Canon EOS 7D mark II at ISO 6,400. Due to the high noise levels, some details are lost.

Which Is the Better Choice?

It all comes down to this question: what is the best thing to do? Should you choose a crop camera to benefit from the gain in focal length, or should you go for the full frame camera and use a post-processing crop?

Before I answer this question, you have to take the high resolution of full frame sensors into account. I took my Canon EOS 5D Mark IV as an example, but if you have a Sony A7R IV or a Nikon Z 7, the number of pixels per square millimeter will reach up to the same levels as the Canon EOS 7D Mark II. On the other hand, the increased resolution of the new Canon EOS 90D balances the differences again. You could calculate the difference yourself if you want.

The Nikon Z 7 is an amazing camera. I loved using it, and it has an amazing resolution, allowing a decent crop without loosing too much detail

The Nikon Z 7 is an amazing camera. I loved using it, and it has amazing resolution, allowing a decent crop without losing too much detail.

From that point of view, I would definitely recommend choosing a full frame sensor and cropping the image yourself. It will also give the flexibility of using the large field of view when using wide-angle lenses and the possibility to play with a nice shallow depth of field more easily. 

From the other point of view, the smaller sensors will allow smaller cameras and lenses compared with the full frame. The micro 4/3 sensor, like in the Panasonic Lumix DC-G9, makes it so much easier to travel with long focal length lenses. And I guess that can be a real benefit for a lot of photographers. And regarding the increased noise levels compared to full frame sensors, I wouldn’t worry about that too much, unless perhaps when you need the highest ISO levels possible.

Using a 100-400mm lens on a Panasonic Lumix DC-G9 is very user friendly. It small size makes it easy to carry with you, and easy to use. The result at 400mm on this MFT camera is similar to a 800mm lens on a full frame.

Using a 100-400mm lens on a Panasonic Lumix DC-G9 is very user friendly. Its small size makes it easy to carry with you and easy to use. The result at 400mm on this MFT camera is similar to a 800mm lens on a full frame (Photo by Hetwie - www.hetwie.nl).

If you had decided at this moment between a crop sensor or to crop a full frame image, what would you choose and why? I would love to read your experience and opinion on this subject. I think it would also be a great help for those photographers that have to make a choice in the near future.

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108 Comments

Jerome Brill's picture

I've done many tests between my A7R III and A6000. It always seemed better to just crop the A7R III image. For two main reasons, one, your crop isn't always going to go down to the size of the crop sensor. A lot times you'll still be at a higher resolution. At-least in the case with 42mp vs 24mp. If I had the A7R IV I wouldn't even have the A6000. The second is iso. Once you get above a certain threshold on a crop body the image is either usable or you're going to spend more time in post. Base iso's with plenty of light ,it's mostly apples to apples unless you're specifically looking for dynamic range which some crops might lack. In the end, invest in longer pro lens.

Nando Harmsen's picture

You have a good point, if you crop a full frame image, you can crop as much (or little) you like.
About the ISO, it all depends on the camera you are using. I understand you have experience with the A6000. Other camera's may have a better ISO performance.

Jerome Brill's picture

I'm generally speaking between the same brand. Some crops are better than other crops, that is true. Not necessarily better than their full frame counterparts. This comes into play with most people since they will stick with a single brand. Personally my a6000 was just replacement my Canon 70D after I sold it. Although I don't really use it, I should probably sell that too.

RT Simon's picture

I programmed my A7RIII to use the crop sensor mode to get extra reach at 400mm, effectively turning a 400mm @ 42 mp to simulate 560mm @ about 24 mp.
I realize this is just like cropping in post, but it seems to have a greater stabilizing effect when shooting a live performance, and the images in these situations seem to be consistently sharper in low light conditions.

Jerome Brill's picture

Well 400mm is 400mm is 400mm. There are certainly reasons to use crop mode. One might be to fill your frame with focusing points edge to edge. As for resolution, the A7RIII crop mode drops down to 18mp. If I feel I'm going to crop more than 18mp compositionally wise I might do that. However I rarely remember to switch it so I just crop in post. I might try it more now to see if that helps with stabilization. Generally I don't care to fill the frame with my initial shooting unless I'm focusing manually. I do have that set to 6.2x. It's still best to get as close as you can so you don't have to crop as much. Although I know that's easier said than done.

Kurt Hummel's picture

I used to have a crop 7D2 along with my FF 5dsr that I use on my 600/4 IS II. I got rid of the 7D2 after a year and picked up a 1DX2, I never saw a benefit for the crop body.

Nando Harmsen's picture

Well, not everyone can afford such equipment. For you it has no benefit, but for those who have only a limited amount of money to spend it may give a lot of benefit. :)

Deleted Account's picture

As long as you are using the same focal length on both cameras and have sensors with the same pixel density, it literally makes no difference...

Brian O'Callaghan's picture

But isn’t the smaller sensor gathering less light? So gain in focal length has to be set against loss on the f stop.

Nando Harmsen's picture

No, that is a myth. The amount of light that goes through the lens doesn't change. Crop sensors don't effect aperture at all

Brian O'Callaghan's picture

I understand that the light coming through the lens is the same. But a third of it is missing the sensor. If you could get greater reach/magnification and yet retain quality simply by making the sensor smaller then that's what everyone would do and we could all give up carrying around big lenses. I'm very much an arts and humanities person not a scientist, but in applying the crop factor to the focal length aren't you changing one side of the equation without applying the same maths to the other side? So don't you have to apply the crop factor to the f stop as well? Otherwise why wouldn't I attach my 400mm lens to my iPhone and photograph Mars?

Nando Harmsen's picture

Of course, Brian. A third is missing the sensor, but as Károly Zieber is mentioning, the amount of fotons that is hitting the sensor per square mm stays the same. Exposure does not change at all. So it crop factor doesn't apply to the f-stop.

Károly Zieber's picture

What you may meant is, because of the bigger image circle, a crop sensor will not utilize the total number of photons getting through during exposure. The number of photons hitting a sensor is only affected by the f-stop and shutter speed. Number of photons/mm^2 is the same, but SNR differs in favour of the bigger sensor, not concerning anything else, but size.

Tony Northrup's picture

If money is no object, a FF 5DSR, D850 or a7R IV are the best choices. You'll still have to crop for wildlife, but having the FF field of view when shooting is really useful, especially for flying birds. If you're looking for good results in a light and compact body, we found that a Sony a6400 with their 200-600 or a Nikon D500 with their 200-500 outperformed the Olympus lenses.

Erpillar Bendy's picture

I don't trust you.

Matt Williams's picture

Tony: "if you're looking for good results in a compact body, here's my example of a small body with an absolutely enormous $2000 lens on it. Clearly this is an appropriate comparison to Olympus."

Matt Williams's picture

Hey Tony can you show me a lens with the same size, price, and IQ for that Sony or Nikon that can get the reach of an Olympus 75-300 or Panasonic 100-300?

You can even ignore the price part if you want.

Best of luck.

Deleted Account's picture

Same size and price are obviously not going to happen. You need a bigger lens to cover a larger sensor area at an equivalent field of view. Bigger lens for the same IQ is going to cost more.... As far as coverage, Tamron or Sigma's 150-600mm should give you the same coverage as a 75-300mm on m43 and I'd wager that the IQ is comparable. Honestly, IQ on just about any modern lens is going to be good enough that you'd be hard pressed to tell them apart.

All that having been said, I'd put the AF of a Sony, Canon DSLR, or Nikon DSLR over an Olympus or Panasonic any day of the week, which is a pretty important consideration if you're talking about wildlife photography with long lenses. I'm not really sure how Canon's MILC performs with AF in that area and I'd wager that my Z7 wouldn't do nearly as well as a D850 for that application.

Matt Williams's picture

Tony said "If you're looking for good results in a light and compact body" and then mentioned Olympus.

He brings up an a6400 - a tiny camera, then suggests putting an enormous $2,000 lens on it. And then compares that to Olympus. The D500 is a great camera and with the Tamron 100-400, which is a brilliant lens, you get some excellent reach.

But in no way is it comparable to an E-M1 Mark III with a xx-300mm lens. It's just a silly comparison to make, obviously the larger sensor will perform better than the smaller one. So if you're going to compare them, you need to acknowledge the massive difference in size.

And you shouldn't doubt the AF and tracking capabilities of an E-M1 III or E-M1X, not to mention the frame rates, of which only a Sony a9 can compete with. Panasonic is a different story as they use DFD and don't have phase detection.

He'd probably respond with something about depth of field, because that's what he talks about half the time.

Michael L's picture

"FF field of view when shooting is really useful, especially for flying birds. "

In bright light a higher pixel density crop camera with appropriately shorter lens is going to be better, autofocus tracking aside. More pixels on target, or same number of pixels but a wider field of view (so more likely to keep the bird in frame), with no appreciable noise difference.

Matt Williams's picture

And on a DSLR, e.g. D500, the AF is usually taken from a FF model (D5 in its case I believe), meaning the AF points cover more of the frame than in the FF model.

Nando Harmsen's picture

I reviewed the D500 and I was surprised about the amount of AF points and the coverage accross the viewfinder. It is more than on a a full frame, indeed.

Nando Harmsen's picture

For most people money is an object.

Momchil Yordanov's picture

What Tony says is true. I have tested the D500 and the E-M1 II, using the 200-500 and the 300 prime respectively and the Nikon was winning in IQ. With D500 and the 200-500 you have a 750 eq. And at 5.6 you have roughly the same amount of light hitting the 20mp sensor as with the micro lens at 4, and the same 20mp in the Oly. Plus the bigger sensor has better DR and you can apply heavier edit to the RAWs. Basically, when you are comparing a 750 eq and a 600 eq with all the rest being roughly equal, no wonder the bigger reach wins. Plus it's less expensive, because the 300/4 is a lot of money. Having said that, the Olympus combo was so much lighter, you really feel it. And also, (as a side-note) the E-M1 II is much more usable outside of the woods. I was just carrying it around with the tiny 25/1.8 and it was fun. While D500 is a brick, that cannot shoot in silence. You don't take these to the restaurant...

Nitin Chandra's picture

Do check out this video and comment. Would appreciate any feedback...

https://youtu.be/NfBiRo5Q40k

Michael L's picture

If you could just ignore physics, the ideal camera would have 360 degrees fov and arbitrarily large pixel density and then you'd just crop as needed.

Closer to the real world, assuming identical pixel density and sensor efficiency, there will be no difference between an image taken from an APS format camera with a given lens and a 135 format camera with that same lens, cropped to the same framing as the APS camera.

In the actual real world: for a given focal length, a Canon 90D or M6ii has more reach than any 4/3 camera, because reach is just pixels on target. You could crop down to 4/3 size and still have more pixels. And also more reach than any current 135 format camera.

Nando Harmsen's picture

Even if you ignore physics, a 360 degrees camera would not be ideal, in my oppionion. There is more to a picture than just capturing everything and cut out the thing you need.
Besides that, you are right asuming the thing closer to the real world. The actual real world depends on the pixel density of the sensor. And don't forget the downsides from a higher pixel density: ISO noise levels.

Malcolm Wright's picture

It's not so much anything to do with sensor size 'crop or full frame', as to do with usable pixel count (viewable pixels). Provided the image is captured well on the sensor everything currently gets cropped to view it.

A HD screen 1920 x 1080 pixels is around 2mp, a 4k screen is around 8mp.
So micro 4/3 16mp sensor is overkill by either 8x or 2x, a 24mp sensor is 12x or 3x overkill. A 42mp sensor is 20x or 5x overkill.

I won't even start on potential print sizes at 300dpi.

So a good modern camera is more than capable.

With regard to field of view differences, the article makes a good point of the wider field of view being useful in capturing moving objects. To achieve the same field of view on a cropped sensor use a wider lens. You could then crop as you would on a 'full frame' sensor, if both cameras had 24mp sensors you'd have the same picture displayed.

It might even be argued that a crop from a 24mp sensor could give a better result if it's easier for the display equipment to interpolate.

Of course once display equipment becomes 8k or greater, most of us will need cameras with higher pixel counts, unless the display equipments extrapolation is excellent.

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