Is "magnification" an advantage of crop sensor?

[New Daddy]

I think I'm finally getting the hang of the sensor size concept.

So, it looks like the smaller camera size and lens size are definitely an advantage of a crop sensor camera (i.e., less than full frame). But is the "magnification" factor an advantage too? I thought if you had a Canon APS-C camera, that gives you an x1.5 "advantage" in magnification and lets you carry a smaller focal length to do the same job.

But is it really an "advantage"? After all, the image you'd get with an APS-C camera is the same image you'd get if you shot with the same focal length and distance from the subject on a full-frame camera, cropped the middle 50% of the image and enlarged it in the final print. There should be no loss of resolution in doing so. Then, the extra "reach" of crop sensors is an extra reach in the viewfinder only, and not in the final image, which was possible all along with a full-frame camera if you wanted.

Am I thinking correctly?

[Davey]

no magnification is the same but field of view is different as you say. There is a lot of misinfo regarding the crop magnification thing and I've even heard pros say it sometimes (something I am not). Basically ff35mm lens will produce 35mm of image circle (actually the sensor is 36ish and lens image a bit more but for sake of simplicity I'll say 35mm for both); cropped canon on other hand is 22mm (approx as often 0.2 is more and nikon slightly bigger again) so only captures 22mm of that 35mm lens projection/image.

The image made by the lens is identical in both cases just the cropped sensor is effectively cropping the proportions as capture time. The only real benefits are price, crop specific glass is much lighter an cheaper, bodies are lighter, and some 35mm specific glass that suffers from vignetting and very soft corners etc can be excellent on crop due to it not using the out edges of image.

edit: Reach is the same but field of view gets smaller the smaller the sensor for a given focal length. Opposite is true going the other way hence some telephoto dslr focal lengths are wide-ish for large and maybe medium format depending on what. Also bigger sensors often have bigger pixel pitch (in reasonably similar Mpix rating obviously) so noise is often less of an issue.

[Manfred M]

If you want to be technically correct, a Canon crop sensor has a 1.6x "advantage" over a full frame sensor; Nikon is 1.5x.

That being said, it is less about advantage / disadvantage, but rather looking at the trade-offs between the various options one can look at. I shot both a crop frame (Nikon D90) and full frame camera Nikon D800), and understand the tradeoffs with the two formats. If you wanted additional magnification, on an interchangeable lens camera, then mFT (micro four-thirds) with its 2x crop factor would be even better than APS-C.

What you are not looking at is pixel pitch, i.e the size of the actual sensors in the camera in the two formats. If you took the same image with a 18MP crop frame and full frame, your crop frame would give you higher resolution, because you are shooting with a much finer sensor pitch, and using the crop frame would give you a higher resolution image. On the other hand, a full-frame camera, with larger sensors, would give you lower noise and let you shoot at a faster shutter speed, so depending on the shooting conditions, you might end up with a better image with the crop frame or with the full frame. My 36MP D800 has roughly the same pixel pitch as the 16 MP Nikon D7000, so your cropping scenario would be about the same if I shot the same scene and cropped the D800 shot. On the other hand, the 24MP D7100 APS-C sensor would technically give me a higher resolution image. One has to factor in the lens one is using as well. A high end lens that you will tend to use on a full-frame camera is potentially going to give you a sharper shot than a lower end lens on a crop frame, but only if you use it to its full potential, large print, etc.

If life were only that simple...

As a photographer, you are always deal managing trade-offs, and it is important to know how to balance off the various features of the cameras. Large sensors do have advantages (image quality) and downsides (costs), but the choices really mean understanding what the various tradeoffs mean to you as the photographer.

[revi]

(...)

What you are not looking at is pixel pitch, i.e the size of the actual sensors in the camera in the two formats. If you took the same image with a 18MP crop frame and full frame, your crop frame would give you higher resolution, because you are shooting with a much finer sensor pitch, and using the crop frame would give you a higher resolution image. On the other hand, a full-frame camera, with larger sensors, would give you lower noise and let you shoot at a faster shutter speed, so depending on the shooting conditions, you might end up with a better image with the crop frame or with the full frame.

If you were indeed taking the same image (i.e. same viewpoint and same angle of view), there should be no difference in resolution: your cropped frame pixel pitch might be smaller, but the image on the sensor is smaller as well.

As an aside, I never heard that full frame gives you a faster shutter speed (given F and ISO settings). Unless you mean that a full frame allows a higher ISO setting for a given noise level (and then of course you get a faster shutter speed).

(...)
If life were only that simple...

As a photographer, you are always deal managing trade-offs, and it is important to know how to balance off the various features of the cameras. Large sensors do have advantages (image quality) and downsides (costs), but the choices really mean understanding what the various tradeoffs mean to you as the photographer.

One reason for the cost difference (and which makes crop frame equipment lighter): for a given angle of view, the crop frame will use a shorter focal length. That means that it will have less glass for each element. Thus less surface to shape and polish correctly...
So a 100mm F4 on a 1.5× crop frame will be equivalent to a 150mm F4 on a full frame, but the latter will have about twice the glass surface, and close to 3× the weight (lens thickness has to increase as well...)

There also tend to be differences in build quality between cop and full frame bodies, with the full frames being the high end of the market. Same with lenses, but afaik, you can use top level FF glass on a crop body (focal lengths will be a bit odd, and you'll miss out on the more extreme wide angle lenses)

[Colin Southern]

In simple terms ...

Assuming that the two cameras you're comparing have similar mega pixel counts (crop -v- full frame can only ever be a comparison that takes pixel counts into account) then the 1.6 or 1.5 crop-factor camera will have around 50% more effective reach.

Yes - there are (many) other factors, but assuming that you're avoiding the extremes, then that's basically the "rub" of it.

[jcuknz]

If you are looking for a convienient tool as opposed to something which takes technically great images there is a definite advantage in using a MFT camera where everything is smaller and lighter than either APS-C or full frame, or larger.
If I was going for the second option I would get myself a FF camera. In places were it is possible an option is to hire the bigger format perhaps even digital MF for when it is really needed.

[TonyW]

Colin, what you say is true only if the lens used has the resolution to take advantage of the smaller pixel pitch on the crop-frame camera. There could be examples that I am unaware of but I thought that up to now top end full frame cameras have more pixels than crop-frame cameras.

[Colin Southern]

Colin, what you say is true only if the lens used has the resolution to take advantage of the smaller pixel pitch on the crop-frame camera. There could be examples that I am unaware of but I thought that up to now top end full frame cameras have more pixels than crop-frame cameras.

Hi Tony,

Pixel counts always enter the equation, but - if one avoids the "extreme" cameras - you'll probably find that most are around 18MP these days, so if one compares an 18MP crop with an 18MP FF then the crop wins the reach dept whilst the FF wins the wide-angle race.

To give you a real-world resolving power scenario though, an associate of mine was shooting a sports event with a Canon 1D3 and 70-200mm lens (10.1mp, 1.3x crop-factor) and I was shooting the same event with a Canon 1Ds3 and 70-200mm lens (21MP, FF). He "claimed" the reach advantage by virtue of the fact he was using a crop-factor camera but in reality, I out resolved him by around 30%. If you have something like an 8MP 1.6 crop-factor camera -v- a 21 MP FF camera then in terms of resolving power, it's actually very close. If you have something like, say, a 24MP FF camera and an 18MP 1.6x crop-factor camera then the 1.6x crop-factor camera will win the "pseudo focal length advantage race" by a huge amount. If it were something like a 36MP FF camera -v- a 18MP crop then I don't know what the result would be (I haven't done the math) (best guess is a small win to the crop-factor camera). So - in summary - pixel counts always enter into it (1.6 crop factor = 1.6x FOV advantage but NEVER equals 1.6x resolving power advantage unless MP counts are the same). In terms of resolving power it takes a truckload more pixels on the FF camera to out-strip the smaller sensor size of a crop-factor camera.

In terms of lenses limiting things - possibly on low-end lenses - it's never been an issue for high-quality glass in my experience.

[Manfred M]

If you were indeed taking the same image (i.e. same viewpoint and same angle of view), there should be no difference in resolution: your cropped frame pixel pitch might be smaller, but the image on the sensor is smaller as well.

Agreed, but only if you enlarge the image the same amount. In reality, we will look at the final images at the same size, so the crop frame image will require more magnification. View things on a computer screen, and it really isn’t going to buy you anything, as both crop frame and full frame are going to be downsampled to fit on the screen. Print large format, and there will be a difference.

As an aside, I never heard that full frame gives you a faster shutter speed (given F and ISO settings). Unless you mean that a full frame allows a higher ISO setting for a given noise level (and then of course you get a faster shutter speed).

Exactly what I meant to say.

One reason for the cost difference (and which makes crop frame equipment lighter): for a given angle of view, the crop frame will use a shorter focal length. That means that it will have less glass for each element. Thus less surface to shape and polish correctly...
So a 100mm F4 on a 1.5× crop frame will be equivalent to a 150mm F4 on a full frame, but the latter will have about twice the glass surface, and close to 3× the weight (lens thickness has to increase as well...)

There are a number of reasons why crop frame lenses are less expensive, but as someone who has spend many years working in an engineering role in product manufacturing and mass production, I can’t agree with your cost assessment. In general, crop frame lenses, versus pro lenses, tend to be slower (smaller maximum aperture) so the light does not have to be bent as acutely, and that is why the elements tend to be smaller and less of them. The construction tends to be cheaper as well. The actual material costs only make up a portion of the cost; labour, manufacturing overhead, R&D amortization and tooling amortization are going to make up a signification portion of all of these costs. Assuming that you sell 100,000 units of a crop frame lens and 10,000 units of a pro lens; if you sink the same amount of R&D / tooling costs into both, the crop frame unit cost will only have to carry 1/10 of those costs per unit. In addition, I would look at different types of tooling and manufacturing techniques for a production run of 100,000 units than 10,000 units, you start seeing some of the reasons for the lower costs.

There also tend to be differences in build quality between cop and full frame bodies, with the full frames being the high end of the market. Same with lenses, but afaik, you can use top level FF glass on a crop body (focal lengths will be a bit odd, and you'll miss out on the more extreme wide angle lenses)

The same argument that is made for lenses is also true for the camera bodies. A full-frame pro body is die cast metal, where as a consumer DSLR tends to be injection moulded plastic. After paying for the tooling, the actual production costs for a high-pressure injection moulded body is going to be a fraction of the cost of a die cast metal body. A glass pentaprism and shutter that are rated at 200,000 cycles are going to be a lot more expensive than a pentamirror and shutter assembly rated at 100,000 cycles, etc., etc.

[chauncey]

My basic points with using that crop sensor has boiled down to "more pixels on target" and the fact that you're using the centermost/"sweet spot" of the lens. Check MTF characteristics.

[revi]

Agreed, but only if you enlarge the image the same amount. In reality, we will look at the final images at the same size, so the crop frame image will require more magnification. View things on a computer screen, and it really isn’t going to buy you anything, as both crop frame and full frame are going to be downsampled to fit on the screen. Print large format, and there will be a difference.

I still cannot agree: as we are talking about exactly the same image as taken, we have for both the same angle of view.
This angle of view will correspond to the same number of pixels on the sensor. And that, in turn, translates to the same number of pixels in the final print.
Or in other words: an object that covers 100 pixels in the image of the FF, will also cover 100 pixels in the crop frame. And 100 pixels in the final full-sized print...
cf. Colin's post above.

There are a number of reasons why crop frame lenses are less expensive, but as someone who has spend many years working in an engineering role in product manufacturing and mass production, I can’t agree with your cost assessment. In general, crop frame lenses, versus pro lenses, tend to be slower (smaller maximum aperture) so the light does not have to be bent as acutely, and that is why the elements tend to be smaller and less of them. The construction tends to be cheaper as well. The actual material costs only make up a portion of the cost; labour, manufacturing overhead, R&D amortization and tooling amortization are going to make up a signification portion of all of these costs. Assuming that you sell 100,000 units of a crop frame lens and 10,000 units of a pro lens; if you sink the same amount of R&D / tooling costs into both, the crop frame unit cost will only have to carry 1/10 of those costs per unit. In addition, I would look at different types of tooling and manufacturing techniques for a production run of 100,000 units than 10,000 units, you start seeing some of the reasons for the lower costs.
(...)

You're right, I oversimplified way too much for the costs. I was actually more interested in the weight difference between the two, which is why I tried to restrict myself to the same max aperture. The price tag of a basic lens (of given focal length and max aperture) will indeed also be lower than that of a top quality lens (e.g. the Canon 50F1.4 vs. the 50F1.4 L: 500€ vs 1300€...)

[RobertsMx]

I think I'm finally getting the hang of the sensor size concept.

So, it looks like the smaller camera size and lens size are definitely an advantage of a crop sensor camera (i.e., less than full frame). But is the "magnification" factor an advantage too? I thought if you had a Canon APS-C camera, that gives you an x1.5 "advantage" in magnification and lets you carry a smaller focal length to do the same job.

But is it really an "advantage"? After all, the image you'd get with an APS-C camera is the same image you'd get if you shot with the same focal length and distance from the subject on a full-frame camera, cropped the middle 50% of the image and enlarged it in the final print. There should be no loss of resolution in doing so. Then, the extra "reach" of crop sensors is an extra reach in the viewfinder only, and not in the final image, which was possible all along with a full-frame camera if you wanted.

Am I thinking correctly?

If you crop, you're losing resolution (and you can still crop APS-c too). So, crop sensor does have an advantage in optical reach.

[New Daddy]

If you crop, you're losing resolution (and you can still crop APS-c too). So, crop sensor does have an advantage in optical reach.

That is only if photosite density on the sensor is different. If the photosite density on the sensor is same (i.e., same number of photosite per unit area), then you don't lose resolution by cropping. I think there are numbers out there saying that 31MP full-frame sensor has equal density of photosites as 12MP crop sensor, or thereabout. I think Colin nicely explained this above.

[xpatUSA]

Perhaps I should not post because it could be a waste of everybodys time.

Have we now generalized the word "magnification" so it can be jumbled up with other general words like "resolution", "optical reach", "photosite density", etc.?

Since magnification is, in fact, the subject size at the sensor divided by the actual subject size in the scene, magnification is not a property of the sensor and is not, therefore, an advantage of any one sensor size over another.

Probably too pedantic . . . I'll get my coat . . .

[DanK]

Since magnification is, in fact, the subject size at the sensor divided by the actual subject size in the scene, magnification is not a property of the sensor and is not, therefore, an advantage of any one sensor size over another.

I think this is not that hard to sort out in a way that will make sense for newbies.

Yes, technically, magnification is the ratio of image size on the sensor to subject size. However, folks often have another ratio in mind, because relatively few of us have reason to be concerned with the image size on the sensor. Instead, they think of magnification in terms of image size relative to the frame. That is, they are thinking: "given this lens and my distance from the subject, how much of the frame will the subject fill?" That is a very reasonable question, and one that is often more relevant for most folks than magnification in the technical sense. And in lay parlance, this second is also "magnification". In our terms (mine, at least), it is "reach", not "magnification.

Once this is explained to newbies, the rest is relatively easy to explain. Sensor size has nothing to do with magnification, but it has a major effect on reach.

Re the OP's question: is this an advantage of a crop sensor? It can be, depending on what you are doing. if you plan on posting the web, don't worry about it: images on the web are so coarse that it won't matter. However, if you really need the pixels, then it can--for example, if you need to crop, or you intend to print relatively large. I'll give you two examples. I do a lot of macro work. The greater pixel density of crop cameras is very helpful, as I get more pixels on the bug or flower and have more flexibility to crop. Another example: in mid-October, if the weather is good, I am planning an early morning shot of the High Peaks of the Adirondacks from across Lake Champlain. The gibbous moon will be setting over the mountains shortly after sunrise, and the leaf colors should still be bright. Even with a crop camera, i will be using my longest lens and will need to crop, and I intend to print the picture.

Of course, there is no free lunch. The lower pixel density of FF cameras has a lot of advantages, such as lower high-ISO noise and a higher diffraction limit. The tradeoffs depend on what you do.

OP: BTW, welcome to the forum. Our custom here is to add our real names and locations to our profiles. Can you please do that?

Dan

[Colin Southern]

I think this is not that hard to sort out in a way that will make sense for newbies.

Yes, technically, magnification is the ratio of image size on the sensor to subject size. However, folks often have another ratio in mind, because relatively few of us have reason to be concerned with the image size on the sensor. Instead, they think of magnification in terms of image size relative to the frame. That is, they are thinking: "given this lens and my distance from the subject, how much of the frame will the subject fill?" That is a very reasonable question, and one that is often more relevant for most folks than magnification in the technical sense. And in lay parlance, this second is also "magnification". In our terms (mine, at least), it is "reach", not "magnification.

Once this is explained to newbies, the rest is relatively easy to explain. Sensor size has nothing to do with magnification, but it has a major effect on reach.

Re the OP's question: is this an advantage of a crop sensor? It can be, depending on what you are doing. if you plan on posting the web, don't worry about it: images on the web are so coarse that it won't matter. However, if you really need the pixels, then it can--for example, if you need to crop, or you intend to print relatively large. I'll give you two examples. I do a lot of macro work. The greater pixel density of crop cameras is very helpful, as I get more pixels on the bug or flower and have more flexibility to crop. Another example: in mid-October, if the weather is good, I am planning an early morning shot of the High Peaks of the Adirondacks from across Lake Champlain. The gibbous moon will be setting over the mountains shortly after sunrise, and the leaf colors should still be bright. Even with a crop camera, i will be using my longest lens and will need to crop, and I intend to print the picture.

Of course, there is no free lunch. The lower pixel density of FF cameras has a lot of advantages, such as lower high-ISO noise and a higher diffraction limit. The tradeoffs depend on what you do.

OP: BTW, welcome to the forum. Our custom here is to add our real names and locations to our profiles. Can you please do that?

Dan

Perhaps to put this another way ...

Although the magnification doesn't change, often, the pixel density does, because often the manufacturers will cram more pixels per square millimeter into a crop-factor camera than they do into a full frame camera. On the PLUS side, doing this really does give a pseudo focal length advantage - however - on the "no such thing as a free lunch" theme, the MINUS side is that the smaller pixels don't gather as much light and so noise levels are higher and thus dynamic range is reduced.

[RobertsMx]

That is only if photosite density on the sensor is different. If the photosite density on the sensor is same (i.e., same number of photosite per unit area), then you don't lose resolution by cropping. I think there are numbers out there saying that 31MP full-frame sensor has equal density of photosites as 12MP crop sensor, or thereabout. I think Colin nicely explained this above.

Most FF sensors are 20-24MP. Some of these cameras can also be used in crop mode (24mp reduces to 10 mp). It is not ideal to crop images, regardless of the sensor, if you can get optical reach.

[Colin Southern]

.39 is the Magic Number working between FF and Canon 1.6x crop sensor equivalents.

So ... 18MP 1Dx would be at a focal length disadvantage to any crop factor camera over 18 x .39 = 7.02MP

and

If one had an 18MP crop-factor camera then one would need a FF camera with 46.15MP to have the same resolving power over that portion of the image circle.