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Old 2nd August 2019
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Re: If Sensor Size Doesn't Matter, Why Buy a Bigger One?

There are really only two differences in theoretical terms:

- Larger sensors give shallower DoF for a given field of view. A 50mm lens on FF gives a similar field of view to 25mm on m43. Point them both at a subject a metre away and set them both at f2.8. The FF shot will give you a DoF of about 6cm, whilst the m43 shot will give you nearer 13cm. To get the same DoF on m43 you'd need an f1.4 lens. (Calculations using a CoC of 0.03mm on FF and 0.015 on m43 - the frame diagonal/1500).

- Larger sensors (given similar technology) yield lower noise. The difference will be about 2 stops (for regular photo use rather than astro where things change). So, you'll get the same noise shooting on FF at ISO 3200 as you would on m43 at ISO 800, all other things equal. Sometimes that won't matter. Other times it will. Depends on what you're shooting, how much you're cropping, what the final output medium is, what the lighting is like (poor lighting will generally make noise worse even when exposed correctly), ...

In practical terms there are other differences of course:

- Smaller sensor systems generally have smaller and lighter lenses for a given field of view and at a similar f-stop. So, the Oly 300mm f4 is way smaller than the Nikon 600mm f4. However, the Nikon 500mm f5.6 is much closer in size and because the noise performance of an FF sensor is two stops better, you could crop the 500mm to the same field of view and still be better off in terms of total noise than m43.

- Smaller sensor cameras are generally smaller and lighter. Although Olympus are doing their best to equalise this with the E-M1x!

- Smaller sensor cameras and their lenses are generally cheaper than larger systems. Not all cameras and not all lenses - but in general.

- Larger sensors often deliver improved dynamic range. You'll probably get an extra stop or two of DR from a modern FF sensor over the best m43 sensor available today.
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