But I can - and do - use some of the same lenses as the full frame cameras do. The Sigma 30 mm f1.4 or the Sony 85mm f1.8 are some of the highest rated lenses on DXO, and used on the APS-C camera they are equivalent of 45 mm and 137 mm lenses.

As to having to blow up a half frame image with the same pixel count as the full frame image, I honestly do not believe it is as simple as saying it requires twice the magnification to achieve the same result. But I lack the math and physics and understanding to convincingly argue that.

I am hoping someone here does...

You will see very little difference. My answer is based on personal experience shooting with both formats. I shoot only landscape images with a Sony A7R and A6000. Most of my images are shot using a tripod at base ISO. If I upsize the APS-C images to FF the larger images are only slightly better. If I down size the FF to match the APS-C the smaller images are just as good if not sharper. DXO states that there is a difference in dynamic range between the two but I have not seen this difference shooting real images. So if you don't print larger than 16x24" there are many advantages shooting with the APS-C format over FF.

Digital camera sensors convert light to electronic signals. The signals are then processed, amplified and converted to binary data. The image is constructed from said data. If two cameras have the same pixel count but one is full frame and one is crop frame, here's the difference. The pixels, the photo sensitive diodes that gather the light, on the full frame are larger than on the crop frame sensor. The larger the pixel, the more light it can gather and convert into a electrical signal. The stronger the signal, the less amplification needed when converting the signal into binary data. Lowering the amount of signal amplification needed, lowers the amount of electronic noise associated with the amplification, thus less noise converted into the binary data.
Another advantage of the larger sensor is the spacing between each pixel. The closer together the more susceptible the pixels are to heat generated noise. Since the full frame pixels are farther apart, less heat related noise.

The newer generation of digital cameras possess very powerful processors. These high speed processors are capable of detecting and differentiating between actual image data and a good bit of the noise data and filtering it out. That's why you can get pretty darn good images at ISO 16000 when in the past the usable ceiling was ISO 1600.

Better diodes in the pixels and better processors converting the signals to data; none of it amounts to a hill of beans if the glass put in front of the sensor is incapable of getting the details in the light to the sensor.

Today's crop cameras with their high end sensors and super fast processors are capable of producing images almost as good as a full frame but they still can't match the larger pixels light gathering ability, that's just simple physics.

First, please, I am NOT trying to start a flame war here. This is an honest inquiry.

I use an APS-C cmaera, a Sony A-6000 camera, which incorporates a sensor that is 23.50mm x 15.60mm in size, and with 24.3 megapixels. I own three prime lens that are pixel limited in resolution.

Full Frame cameras typically use a sensor that is 24 X36 mm. Recent models offer anywhere from about 24 megapixels to about 50 megapixels at the high end.

My question is this - is there any significant performance difference between a camera using an APS-C 24 megapixel sensor, and a full frame camera using 24 megapixel sensor?

Perceived advantage of the APS-C camera:
1) Smaller, and lighter
2) Cheaper
3) Lenses for a given angular field of view are shorter in focal length - .667 X. Lens are lighter and cheaper for a desired aperture.
4) Zoom lenses designed to cover the smaller sensor are lighter, cheaper and usually sharper.

As the old Greek philosopher said, “There ain’t no free lunch.” I do understand there is a modest improvement in low light performance using the larger sensor. But then I do mostly scenics so that advantage is of little value to me. Smaller, lighter and cheaper do mean something to me. What are the advantages to using cameras with the full frame format?

Bob Locher