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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).

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 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.

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 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.

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 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 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. 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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131 Comments

Previous comments
Nitin Chandra's picture

LoL! No FL will ever be long enough and no magnification will ever be enough for macros...In short, we are all just plain greedy :P

Mike Ditz's picture

This is a very interesting topic to me as I have probably never considered these different concerns that many other photographers get all wrapped up in. More than 75 comments and it seems there are a lot of valid and obscure points being made. Maybe I don't get it but there seems to be a lot of proving how many angels can dance on the head of a pin.
Is this only for wildlife shooting (never done it) or are there practical concerns in other genres...

Nando Harmsen's picture

I think this is mainly for photographers that need long focal length, like wildlife, birds and perhaps sports. And for the amateur that likes to shoot at the zoo, or something like that :)

Ed Sanford's picture

Photography teacher and guru, the late Fred Picker would say to you "try both and determine what suits you best."

Mike Ditz's picture

Probably not going to do that, but it was an interesting glimpse into a part of the photo world that I didn't really know existed.

Nando Harmsen's picture

A very good point. I has opportunities to do so, and have done this. But for photographers that don't have a lot of gear available, it might be interesting to get a loaner for a couple of weeks.

Nitin Chandra's picture

Just IMO, if what you are getting makes you happy, nothing else matters...

Malcolm Wright's picture

Hi Nando

I've been contemplating getting an M43 system, as the pictures my Friend produces with his at my local camera club are outstanding in their resolution. I'm also looking for a lighter system.

Whilst everyone uses crop factor, the actual resolution difference is really nearer crop factor squared. That's because the crop factor is measured on the diagonal. So a full frame sensor at 36mm by 24mm has a surface area of 864 sq mm. An M43 sensor measures 17.3mm by 13mm which works out at 224.9 sq mm.

So to get the same resolution from a full frame crop as a 20mp M43 sensor the full frame sensor would have to carry 77mp.

The same goes for APS-C sensors, a Canon APS-C sensor comes in at 328.56 sq mm so to maintain the same resolution from a full frame crop as a 20mp APS-C sensor the Full frame sensor would have to carry 53mp.

It looks like Full frame cameras are trying to catch up with the improved resolution of smaller sensor cameras, which is also potentially down to the improvements in software coming from mobile phone cameras.

John Spathopoulos's picture

Hello to everyone. I,m John from Greece. I understand that many of you are professionals. I'm just an enthusiast amateur photographer. I didn't have the endless budget. Last year I purchased the Nikon Coolpix P1000. I was thrilled with the zoom it had and how close it can bring practically any desirable subject. So I took a deep breath and instead of buying a dSLR I followed my instinct and went for the Nikon.

Because of the lockdown I didn't had the opportunity to use it a lot till now. I love the versatility of the lens! I can shoot either wide or very far, far away! Whatever I see,I can shoot it in a blink of an eye! Absolute freedom! I understand that with a full frame camera to achieve the same result I would need bulkier and much more expensive equipment. I also understand the cons of my choice. I admit that when I shoot far away, because of the small sensor,I loose detail. Particularly at the characteristics of the faces of the people. You can see the shape of the face (I'm talking now about the 2500-3000mm focal length), but you cannot distinguish the iris of the eye for example. And there is grain at a degree. The skin is not so sharp and glossy as it would be with a full frame camera. But I can't say that the clarity of the image is in a category that you would characterize it "bad". I would characterize it rather "okay". In a good level. On the wide end I can compare it directly with my old camera witch I still possess. Sony DSC-R1. It happens to have a focal length range 24-120mm equivalent with smaller crop factor. To be brief,in comparison to my new one which have 24-3000mm equivalence it differs to one more person in the family photo. Not a big deal. In dark scenes now... Well. That's the reason I'm still keeping the old one!😆😆 I generally try never to exceed the 800 ISO. But, overall the freedom I gained with this camera is simply amazing... I wouldn't exchange it with anything else! And although I don't have too much experience with post processing I don't like the idea to crop from a larger image. I don't know. It feels like it looses something from his greatness. Or magic if you like...

Hachem El Ouggouti's picture

I was wondering what would happen if I took a picture with the same lens on a full frame and then on a crop camera, and if both sensors had the same relative (important!) resolution. Would the quality of both images be the same, or would there be details on one and not the other? I am of course talking about the common parts of both images.

Jacob H.'s picture

Theoretically the images would be very similar, but it is a bit of a strange comparison. If you take a real life example: the X-T4 with 26MP has the same sensor (except for the color filter) as the A7RIV with 61MP. They are just cut to different sizes (APS-C vs. Full Frame). When you would take a 50mm lens on the X-T4 the view angle would be approx. 32 degrees and on the A7RIV it would be 47 degrees. So the Sony would have a much wider shoot than the Fuji (where the 50mm would act as a 75mm, but with the compression of a 50mm). If you would then crop the Sony image back to the view angle of the Fuji image, you'd end up with similar resolution of 26MP and (given the same print size) probably comparable quality. However, when you mount a 75mm lens on the Sony and compare the uncropped images, the Sony using the full 61MP would 'blow the Fuji with it's 26MP out of the water'. It's like comparing me with Usain Bolt. When Usain is only allowed one leg, I'm probably as fast as him (I guess...).

Hachem El Ouggouti's picture

I find the idea that both images would be theoretically identical very interesting. The full frame sensor lies further from the lens than the crop sensor. How could both images be identical?

Jacob H.'s picture

Why would the full frame sensor be further from the lens than an APS-C sensor? In fact my Nikon Z mount has a shorter flange distance than my Fuji X-mount camera.

Hachem El Ouggouti's picture

look up flange focal distance. I could not explain it, but that seems to be the case.

Tom Reichner's picture

Yes, both images would be virtually identical if you cropped the FF image to have the same field of view as the crop sensor image, assuming all else is equal with regards to sensor tech, exposure, light, settings, etc.

And this question that you asked is not at all unusual. It is a question that has been discussed over and over thousands of times on various photography forums. Discussing this comparison is kind of like beating the proverbial dead horse - it has been done so much that one questions the use in doing it again.

Hachem El Ouggouti's picture

Maybe so, but it still does not explain how that is possible. The difference in distance between the back of the lens and the sensor should make for an obvious difference in size, even if the same sensor was used in both cases. You are telling me that it is irrelevant. That is not obvious, even if it may be true. That the small image contains as many details as the larger image is not evident. In fact, it goes contrary to everything that is taught about resolution, everything of importance being equal. So please, bear with me and explain it to me in a way I can understand.
edit: I may be wrong, but I think you are thinking of the case which is applicable to a full frame camera and two separate lenses, one FF, one crop, having the same focal length. In such a case, the crop image would be simply a part of the ff image. In such a case, the problem is inexistant.
When using the same lens with different bodies we start dealing with a different problem entirely. Even if the lens is the same, its separation from the sensor surface is not.
That is the problem I am investigating, and I am hoping for some professional insight.

Tom Reichner's picture

I have used the same lenses on my full frame bodies and my crop bodies for many many years. There is no difference if the resolution per unit area is the same.

For example, I have taken thousands of photos with my 400mm f2.8 lens on both my "cropped" Canon 1D Mark 2 and my full frame Canon 5D, which have the exact same pixel size of 8.2 microns per pixel. Do difference in image quality or detail resolution when all else is equal.

You seem to be making things in your head far more complicated than they actually are. You are considering factors which either don't exist or have no effect on the results.

Why do you think that the distance from the lens to the sensor is different on full frame bodies than it is on crop frame bodies?

Hachem El Ouggouti's picture

That is a very good question. That was indeed an implicit assumption of mine that crop cameras, being smaller, had a smaller distance to the back of the lens. Wikipedia seems to agree with me though.
https://en.wikipedia.org/wiki/Flange_focal_distance

Hachem El Ouggouti's picture

I have another reply pending approval because of a link to a Wikipedia site.
I do not doubt your experience in the matter, which is much greater and deeper than mine. Maybe I am like you said complicating things. It would be good to know also.
I am waiting for some gear to arrive and try it myself. But I certainly do not mind some feedback beforehand.
edit: do you happen to have pictures of the same spot, under comparable conditions, taken with the same lens, a FF and a crop body?

Nando Harmsen's picture

Lenses are built to have a sharp image at a fixed distance; this is de flange distance. It doesn't matter what size the sensor is, it has to be at that distance.
That is why a mirrorless camera, that has a shorter flange distance, need other lenses.

If a cropsensor would have another flange distance, you wouldn;t be able to use the so called fullframe lenses with those sensors. Since you can use full frame lenses with cropsensor, proofs it is on the same distance from the lens.

I have written an article about depth of field with cropsensors. There you can see a couple of examples between fullframe and cropsensor with the same focal length. Perhaps that will help a bit in understanding how it works.
https://fstoppers.com/education/understanding-how-sensor-size-affects-de...
Perhaps this article of mine is also helpfull
https://fstoppers.com/originals/should-i-use-crop-sensor-or-crop-image-f...

The article I wote about cropsensors is in Dutch on my own website, so you probably won't be able to read it.

Hachem El Ouggouti's picture

geen probleem ik zal het zo snel mogelijk lezen.
won't be a problem :)

Hachem El Ouggouti's picture

I have not read the Dutch article yet, but allow me a first reaction.
I don't have the feeling that my question has been answered:
Using the same lens on a FF and a crop camera, would there be any difference between the images after the same relative enlargment?
I am not talking about the depth of field but rather resolution details like two lines close to each other which are distinguishable in one image but not in the other.
Also, there is still the question of how a smaller or larger image gets projected on the sensitive surface. At first I simply talked about the (back) focal point, where all the rays come together and then separate. Obviously they have to do that after exiting the back, and they are not influenced by the aperture size.
I suppose that somehow distance is involved, even if it has nothing to do with the flange?
I still find image formation through a lens puzzling, even though I have read the theoretical explanations many times.

Tom Reichner's picture

Hachem,

I'm sorry, but I don't have comparable photos like that to share here. I never did any controlled tests with that gear. I was more concerned with getting the wildlife images that I wanted to get than I was with getting photos to illustrate the similarities or differences between sensor sizes.

But I can assure you that the distance between the lens and the sensor is exactly the same in full frame DSLRs that have the same mount as crop sensor DSLRs. Whatever difference there is in this distance is purely imaginary and fictional.

Again, I am interested in knowing - why do you think that the distance between one is different than it is in the other? Is it just something you read that made it seem like it is this way, or is this thought of yours based on actual experience with said gear?

Hachem El Ouggouti's picture

Thank you for taking the time to look it up. Concerning the distance between the lens and the sensor, I just could not see how one could get a smaller or larger image projected on the sensor unless one changed the design of the lens altogether. But the Nando confirmed that a crop lens is the same as a FF lens, except the size. That would explain how the image projected by a crop lens is smaller than the one projected by a FF lens.
But I am not sure I got it entirely right. After all, the farther the screen, the larger the image, and only the focus needs to change accordingly. Just like with a projector, right?
edit: i just realized that Nando explained it perfectly: a lens is designed to project a sharp image at a certain distance. So, the problem of the distance has of course been solved beforehand.
That does not mean that distance between the lens and the sensor is irrelevant.

Tom Reichner's picture

Hachem,

I think you have things a little mixed up. In your above post, you use the terms, ""crop lens" and "FF lens". But remember, in your original question you were not talking about different lenses - your whole question was based on using the SAME LENS on a crop sensor camera and a full frame camera.

Not a crop lens. not a FF lens. ONE LENS, used on a crop camera and then on a FF camera.

You said:

"Concerning the distance between the lens and the sensor, I just could not see how one could get a smaller or larger image projected on the sensor unless one changed the design of the lens altogether."

We are NOT projecting a smaller image on a crop sensor camera and we are NOT projecting a larger image on a FF sensor camera. I think this is the root of your misunderstanding - the idea that the image being projected by the lens changes based on what size sensor one is using.

"Just like with a projector, right?"

Let us use your example of a projector and screen .....

Les's say that I have a movie projector and a big screen, let's say the screen is 36 feet wide and 24 feet tall. Now let's say that I set the distance of the projector so that the image it projects perfectly fills the screen. There is no part of the projected image spilling off the edges of the screen, and there is no part of the screen left blank around the edges. The projector-to-screen distance is set so that the image size and the screen size are a perfect fit.

Now let's say that we take the screen down and set up another screen exactly where it was. But this screen is only 24 feet wide and 16 feet tall. We leave the projector exactly where it was. So the projector will be casting the same exact 36 by 24 foot image that it was casting before. The only difference is that the smaller screen only captures a portion of that image. It only gets the center of the image, and the rest of the projected image is cast out into open atmosphere, off the screen, so we cannot see it. We only see the center part of that image. Yet it is the same exact image that we had before with the larger screen.

So it is with cameras and lenses. When you use a lens on a full frame sensor, almost the entire image that the lens is projecting falls on the sensor, hence the sensor is able to record almost all of the image that the lens cast upon it.

Now when we use that same lens on a camera with a smaller sensor, the lens is projecting THE SAME EXACT IMAGE that it was projecting on the full frame sensor. The difference is that because the sensor is smaller, it is only able to capture the center portion of that projected image. The rest of the image is cast off the edges of the sensor, where it is not recorded, so that you will never see that part of the image in your photos.

Once you understand this, I think you will begin to understand why image quality is the same on a crop sensor as it is on a full frame sensor, if we are only talking about the center part of the image that was recorded by both sensors, and if all else is equal with respect to settings, sensor quality, settings, etc.

Hachem El Ouggouti's picture

I think you have a point. But it is way past my bedtime, so I think
"let me sleep on it
I will give you my answer in the morning!" :)

Tom Reichner's picture

You're quoting Meat Loaf lyrics! How clever!

Hachem El Ouggouti's picture

I left the baby baby out though. I didn't think it was appropriate. :)

You are absolutely right. It is quite a logical shift from one lens two bodies, to exactly the opposite!
Your feedback showed me an even more fundamental flaw in my reasoning: I treated digital cameras like they were analog optical devices, while they are in fact computers!
What a digital camera does is optically, physically, impossible. You cannot have a cropped image without a whole image. You have to physically crop the negative.
If you happen to use one of those accordeon thing, extensible focal length, then still, each negative would show the whole scene captured by the lens.
That is what I had in mind (photography was my hobby around 40 years ago!). I am afraid I will have to rethink the whole thing.

Hachem El Ouggouti's picture

I think the only way I can use a digital camera in my case, is to just choose one, ff or crop, and a zoomlens.
I am assuming that the zoom, at all ranges, captures the same scene, but that the image gets somehow enlarged within the lens and then projected onto the sensor. Just like a projector or an enlarger, with a screen or enlarging board of a (reduced) fixed size.

Hachem El Ouggouti's picture

Pictures from camerastuffreview dotcom/test-nikon-coolpix-p1000/

Those two photos illustrate perfectly the problem I am trying to understand.
I understand that simply enlarging the wide angle picture will never give us the second one.
At the same time, isn't it exactly what the camera is doing? The author could have taken one step back before zooming in, to compensate for the lenghtening of the lens and the (negligible) difference in distance to the object, and the result would have been the same.
The same light that supposedly created both pictures entered the lens. Whatever the difference between the two perspectives comes from the zoom.
It seems that an image captured by the lens can be enlarged to quasi infinity! The only limits are technical and practical limits.

Hachem El Ouggouti's picture

This problem does not really belong in this forum. It is more of a (meta) physical problem. Something for physicists and philosophers, more than for (professional) photographers. But professional insight, as this discussion has shown, is indispensable. And there is still a technical matter I wouldn't mind getting some help with.
How does a zoomlens work?
I don't really care about resolution, aberrations or distortions, I just want to understand the basics of zooming.
What would it take to turn a Gallilean or Keplerean telescope (a very simple telelens), into a zoomlens? What would we need to add to the two convex/concave lenses?