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04-18-2013, 11:08 AM   #1
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Ricoh GR f/2.8 vs. Oly E-PM2 f/1.8: Which Gathers More Light?

This is an honest question that is NOT intended to compare the overall relative strengths and weaknesses of the new Ricoh GR versus the Olympus E-PM2. But, for our math wizes out there, which camera gathers more light, or is it a wash? The Ricoh's 28mm f/2.8 lens with an APS-C sensor or the Oly when it is using a Zuiko 17mm f/1.8 lens with a micro four-thirds sensor?

04-18-2013, 11:20 AM   #2
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Technically you mean - at the same light setting, which image ends up with the less noise given same shutter speeds. If it's about gathering light, the faster lens always gathers more light (well, if we ignore Tstops).

If I were to take a guess...

F1.8 to F2.8 is just over 1 stop. An Olympus EPM2 has a rating of 932 ISO on DXOmark, while the Pentax k-5's 16MP sensor is 1162 ISO, or just under 0.5 stops better. So if the sensor on the Ricoh GR is similar to the k-5 sensor, it would perform a little worse in noise than the Olympus EPM2 with the 17 F1.8 lens.
04-18-2013, 11:22 AM   #3
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QuoteOriginally posted by JinDesu Quote
Technically you mean - at the same light setting, which image ends up with the less noise given same shutter speeds. If it's about gathering light, the faster lens always gathers more light (well, if we ignore Tstops).

If I were to take a guess...

F1.8 to F2.8 is just over 1 stop. An Olympus EPM2 has a rating of 932 ISO on DXOmark, while the Pentax k-5's 16MP sensor is 1162 ISO, or just under 0.5 stops better. So if the sensor on the Ricoh GR is similar to the k-5 sensor, it would perform a little worse in noise than the Olympus EPM2 with the 17 F1.8 lens.
Yes, this is a technical, theoretical discussion. And your conclusion is kind of what I'm been thinking - but it's probably pretty close. If anyone has anything to add, I'm all ears.
04-18-2013, 11:32 AM   #4
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The only thing not taken into account is manufacture stated ISO vs measured ISO. For example, DXO shows that the EPM2 will say it is ISO 200, when the measured ISO is 100. The k-5 will say ISO 200, when the measured ISO is 183.

I'm not entirely clear if this affects anything, so I didn't want to put it in.

04-18-2013, 12:36 PM   #5
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QuoteOriginally posted by Biro Quote
This is an honest question that is NOT intended to compare the overall relative strengths and weaknesses of the new Ricoh GR versus the Olympus E-PM2. But, for our math wizes out there, which camera gathers more light, or is it a wash? The Ricoh's 28mm f/2.8 lens with an APS-C sensor or the Oly when it is using a Zuiko 17mm f/1.8 lens with a micro four-thirds sensor?
The GR has the 1.5x crop APS-C sensor. The M4/3 cameras have a 2.0x crop. So there's less than 1 stop of area difference. However, a F/1.8 lens is 1 and 1/3 stops faster than a F/2.8 lens. So the M4/3 camera will collect more light.
04-18-2013, 02:29 PM   #6
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QuoteOriginally posted by devorama Quote
The GR has the 1.5x crop APS-C sensor. The M4/3 cameras have a 2.0x crop. So there's less than 1 stop of area difference. However, a F/1.8 lens is 1 and 1/3 stops faster than a F/2.8 lens. So the M4/3 camera will collect more light.
Exposure on the active area of the sensor will be determined by the aperture. The sensor size doesn't matter there. The exposure for a 1.8 lens on APS-C, Full Frame or m4/3 is all the same. The smaller sensors don't collect all the light, hence the crop. So technically the total light read by the larger sensor is greater, but it's the same over the active areas.
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