# Exposure basics, lesson two point one (& ISO)

Started Mar 19, 2013 | Discussions thread
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 Re: Correction: G3 vs EM5 - Estimates of Ratios of Light Exposure In reply to Jack Hogan, Mar 21, 2013
G3 at ISO=1600 and EM5 at ISO=3200

(For the G3 relative to the EM5), the ratio of the Average RAW channel levels divided by the ratio of the DxOMark "Saturation ISO" ratings is 1.494 EV, but when receiving -0.322 EV less light (due to it's higher Shutter Speed), and transducing -0.236 EV less electrons due to it's lower QE. So, the G3/EM5 ratio of the amount of light received in that case seems to be around:

(For the G3 relative to the EM5), the ratio of the Average RAW channel levels divided by the ratio of the DxOMark "Saturation ISO" ratings is 1.494 EV, but when receiving 0.322 EV more light (due to it's lower Shutter Speed), and transducing -0.236 EV less electrons due to it's lower QE. So, the G3/EM5 ratio of the amount of light received in that case seems to be around:

+ 1.49 - 0.322 - 0.236 = + 0.9358 EV (91.289% more light)

DM, I don't see any squaring of SNRs You can't read off mean values and relate them to electrons/photons/exposure because you do not know each cameras' gain.The only way to get back to relative electrons/photons/exposure is through SNR when most of the noise is shot, which is what I did.

Also, I calculated the difference in QE at these ISOs to be less than 1/6 of a stop, which correlates relatively well with Sensorgen's which you used. On the other hand, I believe mine is more precise because I assume a blackbody radiator at 5000k as the light source, while Bob assumes a green laser

How about a peer review of my post where I show that the lighting under which both the G3's ISO 1600 and EM5's ISO 3200 captures was for all practical intents and purposes identical.above, Bob?

Jack

Are you able to do this calculation for the E520, based on its old studio scene image?

http://www.dpreview.com/reviews/olympuse520/26

Then, if there's any issue with calculations, we at least have two cameras that can provide real world data.

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