Dynamic Range -- what it is, what it's good for, and how much you 'need'

Started Oct 17, 2011 | Discussions thread
Great Bustard
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On 'asking joe'
In reply to boggis the cat, Oct 20, 2011

boggis the cat wrote:

You should ask Joe if that degree of "roughness" is acceptable.

The difference between systems in terms of light collecting ability for lenses using the same f-ratio and photos displayed with the same area is quite simple:

  • 4/3 vs 1.6x: log2 (332/225) = 0.56 stops more light on the 1.6x sensor.

  • 4/3 vs 1.5x: log2 (372/225) = 0.73 stops more light on the 1.5x sensor.

  • 4/3 vs FF: log2 (864/225) = 1.94 stops more light on the FF sensor.

Likewise, we can repeat for the systems displayed at 4:3 (or more square):

  • 4/3 vs 1.6x: 2 x log2 (14.9 / 13) = 0.39 stops more light on the 1.6x photo.

  • 4/3 vs 1.5x: 2 x log2 (15.7 / 13) = 0.54 stops more light on the 1.5x photo.

  • 4/3 vs FF: 2 x log2 (24 / 13) = 1.77 stops more light on the FF photo.

and for the systems displayed at 3:2 (or wider):

  • 4/3 vs 1.6x: 2 x log2 (22.3 / 17.3) = 0.73 stops more light on the 1.6x photo.

  • 4/3 vs 1.5x: 2 x log2 (23.7 / 17.3) = 0.91 stops more light on the 1.5x photo.

  • 4/3 vs FF: 2 x log2 (36 / 17.3) = 2.11 stops more light on the FF photo.

I define "trivial" as any difference less than 1/3 of a stop (0.33 stops), so none of the differences are "trivial", but the difference between 4:3 and 3:2 most certainly has a trivial effect.

But, let's put this into some persective by comparing the f-ratios of lenses on the respective formats that would result in the same light on the sensor for the same shutter speed and the same DOF for the same perspective and framing (equivalent settings):

  • f/2 on 4/3 --> f/2.5 on 1.6x

  • f/2 on 4/3 --> f/2.7 on 1.5x

  • f/2 on 4/3 --> f/4 on FF

Is the difference "significant"? Well, that's for each individual to decide for themselves.

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