Some people raise their eyebrows when I tell them I am an APS-C shooter, which means the crop sensor inside my camera is significantly smaller than the 35mm equivalent sensor of full-frame cameras.
Truth be told, I never owned a full-frame camera and, at the moment, I am not planning to upgrade to it.
Full-frame cameras and the lenses designed for them are more expensive than their crop sensor equivalent, but it is not just about the money.
The main reason for me is that I doubt it would be a real upgrade in the first place!
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I believe there are only two fields of photography that really benefit from a full-frame sensor:
- Portrait photography (or, in general, whatever field of photography where it is desirable to have a subject in focus and everything else nicely blurred).
- Low light (high ISO) photography.
In the above scenarios, the best results are achieved by using fast lenses and shooting them wide open (i.e. at low F-stops, such as 1.2, 1.4, 1.8, etc.).
Now the point: full-frame cameras can take full advantage of the widest aperture indicated on the lens, whereas APS-C cameras cannot.
This is because on crop sensor cameras, you must multiply both the focal length and the aperture indicated on the lens by the crop factor to obtain the values that correctly describe the behaviour of your lens.
On APS-C cameras the crop factor is 1.5, the only exception being Canon (1.6).
Example: a 50mm F1.8 lens only behaves as such on a full-frame camera. On an APS-C camera with a 1.5x crop factor such as mine, the same lens behaves like a 75mm F2.7. Definitely a much narrower field of view and over a stop darker in terms of aperture!
|| 50mm x 1.5 = 75mm
|| 1.8 x 1.5 = 2.7
Most portrait photographers use full-frame cameras to take full advantage of their fast lenses (maximum aperture such as 1.2, 1.4 or 1.8), thus being able to produce a very pleasant, defocused background known as bokeh.
Fast lenses at low F-stops are also helpful if you shoot in low light conditions, so that the sensor will gather the maximum amount of light allowed by your lens. Once again, full-frame cameras perform better than APS-C cameras in these conditions.
Of course, you could still bump the ISO to compensate for the smaller aperture on APS-C, thus making the image as bright but... the higher the ISO, the more grainy the image.
By now you probably see why I am not upgrading to full-frame. Since I am a landscape and wildlife photographer, the limitations above do not really impact my work.
As a landscape photographer, I very often want to have everything in focus back to front and such an effect is more easily achieved on APS-C.
As a wildlife photographer, my main struggle is getting close enough to my subjects to reasonably fill the frame. Since a 300mm zoom becomes a 450mm on my APS-C camera (300mm x 1.5), this is an advantage for me rather than a limitation!
I also love shooting interiors and exteriors and, to have everything in focus, I almost always set my aperture to either 7.1 or 8. This means I do not need to buy an expensive fast lens, because I would rarely (if ever) shoot it wide open anyway!
I want to conclude this post with a sort of disclaimer, just in case one day you see me with a full-frame camera in my hands.
My Sony Alpha 77 Mark 2 has a 24MP, APS-C sensor. That is already quite a lot of megapixels for a crop sensor. On the other hand, I would love to have a 36MP or even a 42MP sensor.
If one day I ever feel the need to have bigger files for my prints, or to be able to crop more into my images while retaining a reasonably high resolution, that day I will definitely upgrade to full frame.
I think a 42MP crop sensor camera would pay a significant toll in terms of image quality in low light conditions.
Why? Consider a full-frame sensor (a) and an APS-C sensor (b) with exactly the same resolution (e.g. 42MP).
The amount of light hitting the sensor per unit time and unit area will be the same for (a) and (b). But since the sensors have the same resolution and (a) is bigger than (b), the amount of light gathered by each pixel will be less on the APS-C sensor (b), because there will be more pixels per unit area sharing the light hitting that area.
In other words, since the sensors have the same resolution (the same number of pixels), the pixels will need to be more densely packed on the crop sensor (b) than on the full frame sensor (a) because the crop sensor is smaller.
I hope it makes sense. A surprisingly high number of photographers ignore these facts ;-)