Do compact and DSLR cameras have the same sensor size if they have the same number of megapixels?

Question

In the analog camera, I understood the impact of using a 35mm film vs using a 70 mm film.

However in digital world, I dont know if the sensor size is the same for compact and DSLRs. In other words, if I use a compact and DSLR both of 12 megapixels and, say, with a lens of 35mm, will there be any difference in terms of resolution of the image?

Asked by Dheer

Answer

Sensor area doesn't determine resolution in the same way as the film era. Back then simply increasing the area of film would yield a similar increase in the size you could print, and therefore the detail you captured. In the digital world sensors can have different numbers of pixels per cm

Both 12MP compact and DSLR will resolve similar levels of detail but the DSLR sensor will be about 5-6 times bigger in each dimension. The extra size tends to provide better low light abilities as well as shallower depth of field at the same f-stop. This is because at the same f-stop a small and large sensors receive the same light per unit area, however a larger sensor receives more light in total leading to a reduction in photon noise. The difference in depth of field is due to the need to use a longer focal length for the same field of view, giving a larger apparent aperture.

Important note:

Differences in light gathering ability, DOF are not absolute and depend on the actual lenses that are available. For example it is true that for a small sensor compact and DSLR with f/2.0 lenses the DSLR will gather more light and have shallower DOF, however if you compare a 35mm DSLR to a medium format camera (with larger sensor) you might find that f/2.0 lenses aren't available for the medium format, so the smaller sensor 35mm DSLR can gather more light and attain shallower depth of field due to the availability of fast lenses.

Second note:

Not all compacts have small sensors, some now have sensors the same size as most DSLRs, such as the Fuji x100, Sigma DP1, the new Canon G1X and the Sony NEX range, and some are in between - e.g. the micro 43rds and the Nikon 1 series.

Answered by Matt Grum

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