Hi, sorry for the longer question but i'm little bit confused about the effect of the sensor size (APS-C, full frame...) to image quality (IQ). Basically each (infinitelly small) part of sensor has the same amount of light, no matter how big the whole sensor is, right? Or to be less abstract: What I think is true is: IQ doesnt matter on the focal length of the lenses (let's ignore shaking hands with long focal lengths and let's supose prime lenses only) IQ is and 'overall' quality of the image, not just specific part (ignore vignetting, sharpness in center and similar details). In other words displaying the picture in 100% size shows better quality for image taken with FF than with APS-C on any part of the image (generally) I guess the IQ of the picture from FF would be better. At least there would be less noise. Comparing ISO 3200 on R6 or 5D MK IV with EOS 90D shows big difference on pages like dpreview. But from my understaning the noise is caused by not having enough light, not by ISO itself. Higher ISO just increases the information on sensor and if signal to noise ratio is small, than higher iso also makes the noise more visible, correct? So this all would mean that image taken with FF has less noise because it somehow got more light than the one taken with APS-C Now for canon's cameras the crop factor is 1.6x, and let's suppose: FF camera with 32MP sensor, 100mm f/2.8 lenses mount on it, ISO 3200, 1/100s. I take a picture from tripod. I put the very same lenses to an APS-C placing it on the same tripod. Again, ISO 3200 and shutter speed 1/100s. Let's say the APS-C has 20MP sensor (so FF resolution and sensor size are both 1.6x more than the ones on APS-C) In this situation I would have two pictures taken with the same lenses from the same spot and with same light conditions (and same ISO and shutter speed). For APS-C I would have the picture that 's perspective is 'zoomed' relatively to FF (the same picture that I would get on FF with 160mm). Finally the question How would the FF have less noise? If I take the 32MP image and I just crop the 'middle' 20MP big center part of it I should have the same image like the one from APS-C (resolution but also the scene on it). But these 20MP comes from that part of FF sensor that is exactly as big as APS-C sensor itself. So the FF got the same amount of light for this particular part of image/sensor like the APS-C. So how can be that the noise is still much lower? And another related question, is f/2.8 of FF equivalent of f/2.8 on APS-C in terms of light (please ignore the depth of field). In other words, in M mode, shutter 1/100, ISO 100, f/2.8 would the image be exposed equaly on FF and APS-C? I hope I make some sense Thanks
Your understanding of the relationship between sensor size and image quality is largely correct. While the individual photosites on a larger sensor don't receive more light per unit area, the total amount of light collected by the sensor is greater. This results in several advantages for image quality, as you mentioned. The reason a full-frame (FF) camera produces less noise than an APS-C camera with the same ISO setting and exposure parameters is that the larger photosites on the FF sensor can collect more electrons. This reduces the signal-to-noise ratio, resulting in a cleaner, less noisy image.
