[sibyrnes]

What is the advantage of a full frame 24 mp camera over a 24 mp aps-c? Does the full frame have better IQ and if so, what are the technical reasons for that? I understand the advantages of a larger "negative" for enlargement, but if they have the same number of pixels how is one better than the other?

[photoptimist]

Larger pixels gather more photons -- the signal part of signal-to-noise is higher.

[alpheios]

On a 24 megapixel fullframe sensor the same amount of pixels is spread over a bigger surface than on the APS-C sensor. That means that each individual pixel can be bigger and therefore capture more photons. That leads to more accurate signal data and therefore more color and luminance accuracy and less noise.

[RoccoStiglitz]

It's all about the amount of light you're able to capture. Crop size has an effect on virtually every measurable variable of an exposure.

Youtu.be

Youtu.be

In this video (even though the main topic is somthing else he explains crop vs fullframe to illustrate it) author does an excellent job explaning how crop factor impacts your photographs. It's a little long but very informative.

[Na Horuk]

Imagine you have a house and one wall has windows. Someone is throwing tennis balls at this wall from the outside. If the wall is many tiny, tiny windows, then you get a smaller amount of tennis balls per window. If you have the same wall with just three windows, then each window will get enough tennis balls in no time. Of course, the problem is that having just a couple massive windows doesn't let you figure out a lot of detail. With many smaller windows you get more "information" (oh, this ball came from the top left; that one came in bottom right).. So its important to have a good balance.
Full frame vs. APSC just means the 'wall' of the house is bigger. The MP count is the number of windows across that wall. You have FF and APSC houses - the FF one is bigger. But if they have the same amount off windows, then the FF one can capture balls more easily.

ugh, I guess the house metaphor is a bit strained, but hope it helps get the point across

Does the full frame have better IQ and if so, what are the technical reasons for that?

The FF with 24MP would have better light sensitivity (less noise) than 24MP APSC. The APSC would have better resolution at that magnification (capture more detail)
But that said, there are other possible differences as well. For example, whether the sensor has AA filter, its recorded bit depth, special technologies (like foveon, xtrans, backlit sensor..). These things can also change the overall 'look' of the captured image. FF sensors are usually top notch, more expensive variants, often with higher bit depth (this is not just sensor, this depends on camera, buffer, chip, sd card write speed), so FF is overall a more premium product. But these days APSC is really good, too.

[sibyrnes]

Thanks for the answers so far. I had thought that the only reason for full frame was more pixels, but a friend showed me his full frame 24mp Nikon and I had to wonder if it had any advantage over my KP due to the larger sensor size.

[jatrax]

a friend showed me his full frame 24mp Nikon and I had to wonder if it had any advantage over my KP due to the larger sensor size.

It would be difficult to really say with certainty as there are far more variables than just the sensor size. What generation of sensor? Whose sensor? What has been done by the camera manufacturer with the data the sensor provides? And so on, and on.

As others have already noted the biggest advantage is that the same number of pixels are spread over a larger area. And all other variables being equal that produces a better image. But rarely are all other variables equal so it is easy to find examples of a 24mp FF that produces inferior images to an APS-C 24mp camera. Depending on your definition of better.

[08amczb]

FF is one stop bigger than APS-C so it gethers one more stop of light. This means one stop better noise performance expecting the same sensor technology and processing. (The KP and the Nikon D500 has one stop advantage comparing to other APS-C cameras, so approximetly has the same performance as a current FF camera.)
With the bigger sensor you also lose one stop depth of field. In some situations it's intented in others not. For example the DA* 16-50 and 50-135 F2.8 aps-c zooms are equvivalent to 24-75 and 75-200 F4 zooms on FF regarding DoF and FoV. In the other direction the FF 24-70 and 70-200 F2.8 zooms are equvivalent to 16-45 and 45-200 F2.0 zooms!
If you shoot at the same DoF (not aperture) then you have the same noise performance, so if you want to make the same image you don't get so much. But it extends your possibilities, becase there are combinations which does not have aps-c equvivalent.
You also gain some image quality, because at the same MP count a less shar lens needed for the same visual quality. (Bigger pixels accept more blur without overlapping to the neighbour.)

[RoccoStiglitz]

There is going to be so much misinformation here.

[clackers]

There is going to be so much misinformation here.

Ah, yep.

[jatrax]

There is going to be so much misinformation here.

ROFL. Yep, it's gonna deep right quick.

[MadMathMind]

Think of it this way: you can get compact and point and shoot cameras with 24MP. Do those do as well as the 24MP APS-C cameras?

[DeadJohn]

I had thought that the only reason for full frame was more pixels, but a friend showed me his full frame 24mp Nikon and I had to wonder if it had any advantage over my KP due to the larger sensor size.

In very general terms, larger pixels are better as light gets dimmer. Smaller pixels offer the possibility of catching more detail when you pixel-peep, assuming that the lens is good enough and your hand/tripod is steady.

There are too many other variables for those generalizations to matter much. Any modern APS-C or full-frame camera is very good, and we're more often limited by our own skills than by our cameras.

[hjoseph7]

FF is one stop bigger than APS-C so it gethers one more stop of light. This means one stop better noise performance expecting the same sensor technology and processing. (The KP and the Nikon D500 has one stop advantage comparing to other APS-C cameras, so approximetly has the same performance as a current FF camera.)
With the bigger sensor you also lose one stop depth of field. In some situations it's intented in others not. For example the DA* 16-50 and 50-135 F2.8 aps-c zooms are equvivalent to 24-75 and 75-200 F4 zooms on FF regarding DoF and FoV. In the other direction the FF 24-70 and 70-200 F2.8 zooms are equvivalent to 16-45 and 45-200 F2.0 zooms!
If you shoot at the same DoF (not aperture) then you have the same noise performance, so if you want to make the same image you don't get so much. But it extends your possibilities, becase there are combinations which does not have aps-c equvivalent.
You also gain some image quality, because at the same MP count a less shar lens needed for the same visual quality. (Bigger pixels accept more blur without overlapping to the neighbour.)

huh ?

[JohnBee]

What is the advantage of a full frame 24 mp camera over a 24 mp aps-c? Does the full frame have better IQ and if so, what are the technical reasons for that? I understand the advantages of a larger "negative" for enlargement, but if they have the same number of pixels how is one better than the other?

For the most part, I suppose FF will hold the advantage in terms of image characteristics.
Though I can't say I'm not entirely convinced this is always apparent given that some APS-C camera's seem to do quite well in terms of image quality.

In addition to this, I've heard people claim that APS-C systems were better suited to applications like wildlife and telephoto, in that it provides an advantage in cropping.