Crop Factor, Low Light and Aperture with m4/3 lenses?

Started Jun 15, 2014 | Discussions thread
Sergey_Green
Sergey_Green Forum Pro • Posts: 11,993
Nice summary

Great Bustard wrote:

50mm f/2.8 on FF is equivalent to ~30mm f/1.8 on APS-C which is equivalent to 25mm f/1.4 on mFT. By "equivalent to" I mean:

  • The same diagonal angle of view.
  • The same DOF for a given perspective (subject-camera distance) and same diffraction.
  • The same total amount of light falling on the sensor for a given shutter speed.

Any differences in noise will be due to differences in sensor efficiency (as opposed to differences in the ISO setting that is used to get the same brightness for a given shutter speed).

Keep in mind that the lower noise of larger formats (since, for a given exposure, as opposed to same DOF and shutter speed, more light falls on the larger sensor) necessarily results in a more shallow DOF, for better or worse. So, unless low noise matters more to you than a deeper DOF, mFT will be a better choice than larger formats for handheld photography in low light.

Very nicely summed up, I would only add few words about the low noise, if I may. Most of the scenes in the world are middle-gray (or reflect about 18% of light), and that is where the larger formats are often ahead regardless of what sensors they have. The dark shadows, on the other hand, is usually not where the least important information in the images is, and can be cleaned without ill-effects to the rest of the captured scene. That is, if anyone is bothered by it.

Here is a good example (this is from LTZ470),
http://acwilli.smugmug.com/Other/Jakes-B-Ball-Jan-2014-EM1-35/

As you can see there is a lot of noise in the images in general, but none of it effects the most important areas (middle-gray), where the most relevant information is. And the difference between larger and smaller formats in these areas is not that far off anyway, even if it mattered, which it does not.

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- sergey

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