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There was a question a week or so ago asking about M4/3 versus FF cameras. Had some extra time today and went ahead and tried to shoot a comparison as it's a topic I likewise encounter frequently on another forum that I won't name.
First some obvious facts:
Sensors in FF cameras are 4X the area of M4/3 sensors and some basic physics applies. Given the same exposure a FF sensor is going to collect 4X the total light collected by a M4/3 sensor. What you get for that is less noise. The dominant type of noise we see in our photos is a function of exposure + sensor area. Bigger sensor = less noise. Likewise DR capacity is tied to sensor area and so bigger sensor = more captured DR as a general rule. Finally, although it's not a given the larger sensor presents the option for more resolution. So if we can take the same exposure with a FF camera and M4/3 camera we're going to see superior IQ from the FF camera in terms of visible noise with the option for more DR if we need it and more resolution if we're using a higher resolution sensor.
But can we take the same exposure with both cameras? That's the constraint I placed in the title. Of course we can just always make sure you have a good sturdy tripod with you when using the FF camera.
The DOF constraint: If you take the same photo with a FF and M4/3 camera (same perspective and framing) at the same f/stop the DOF in the two images will be different. One commonly identified plus for FF cameras is that they render shallower DOF with a fast lens wide open. A 50mm f/1.4 lens on a FF will deliver shallower DOF than a 25mm f/1.4 lens on a M4/3 both shot at f/1.4. That doesn't mean you can't do shallow DOF with a M4/3 camera but the FF equivalent is smoother and shallower. On the other end the landscape photographer typically wants deeper DOF and here the M4/3 has a possible advantage. To get the same DOF that a M4/3 camera renders at f/5.6 the FF camera needs to be stopped down to f/11 -- two stops and that's two stops less exposure. Now the FF can compensate for the loss of those two stops of exposure by slowing the shutter speed -- and there's that tripod I mentioned above. Another alternative would be to raise the ISO of the FF camera but that means you're underexposing the sensor and noise is a function of exposure + sensor area so reducing exposure = more noise. This constraint I understand very well. I mostly take photos when I'm out walking and no way will I walk with a tripod. On a gloomy overcast day would a FF camera give me any IQ advantage given that I'd want the DOF and would have to keep the shutter speed hand-holdable?
So can I shoot the comparison -- these things are notoriously difficult to pull off. I have a M4/3 camera (Olympus E-PL9) with a 16mp sensor and a FF (Leica SL) with a 24mp sensor; not perfect but I can shoot the FF a little wide and crop it. I keep a 35mm lens on the FF so I first tried to just use that. But I don't have a 17mm for the M4/3 so I tried to use my zoom lens, silly me. I did a great job proving that a 35mm Zeiss prime lens is a whole lot better than an Olympus kit zoom. Try again; the crop factor between FF and M4/3 is 2 so I basically need a lens on the FF double the focal length of the lens on the M4/3. Best I could come up with was a 40mm f/2 Ultron on the M4/3 and a 75mm f/2 Apo Summicron on the FF, but that was fortuitous given the 75mm is a tad wide -- there's at least part of my compensation for the resolution difference between the two cameras. The Voigtlander lens sells for 10 times less than the Leica lens but Cosina makes respectable lenses that hold their own.
So two practical constraints then -- I want the same DOF in both photos and a hand-holdable shutter speed. (I did use a tripod for this comparison but settled on 1/40 sec as a minimum hand-holdable shutter speed. I can't hand-hold at 1/40 sec but lots of folks keep telling me they can do that and better so I compromised. In my reality as soon as my shutter speed drops below 1/150 sec I start bracketing for camera shake and experience tells me I need to do that.) I shot the M4/3 camera at f/5.6 for plenty of DOF and at 1/40 sec I was able to optimize sensor exposure at base ISO. That's important; I was able to expose the sensor to full capacity which gives me the best possible IQ from that camera. The FF camera then had to be shot at f/11 to match the DOF and at 1/40 sec. an optimum sensor exposure was off the table so I had to underexpose the sensor of the FF camera. For what it's worth here's the two photos -- both processed in C1 with noise filtering turned off and scissors on the chair the focus point. I think there's scant little difference between them and I'll leave it to you to figure out which is which.
First some obvious facts:
Sensors in FF cameras are 4X the area of M4/3 sensors and some basic physics applies. Given the same exposure a FF sensor is going to collect 4X the total light collected by a M4/3 sensor. What you get for that is less noise. The dominant type of noise we see in our photos is a function of exposure + sensor area. Bigger sensor = less noise. Likewise DR capacity is tied to sensor area and so bigger sensor = more captured DR as a general rule. Finally, although it's not a given the larger sensor presents the option for more resolution. So if we can take the same exposure with a FF camera and M4/3 camera we're going to see superior IQ from the FF camera in terms of visible noise with the option for more DR if we need it and more resolution if we're using a higher resolution sensor.
But can we take the same exposure with both cameras? That's the constraint I placed in the title. Of course we can just always make sure you have a good sturdy tripod with you when using the FF camera.
The DOF constraint: If you take the same photo with a FF and M4/3 camera (same perspective and framing) at the same f/stop the DOF in the two images will be different. One commonly identified plus for FF cameras is that they render shallower DOF with a fast lens wide open. A 50mm f/1.4 lens on a FF will deliver shallower DOF than a 25mm f/1.4 lens on a M4/3 both shot at f/1.4. That doesn't mean you can't do shallow DOF with a M4/3 camera but the FF equivalent is smoother and shallower. On the other end the landscape photographer typically wants deeper DOF and here the M4/3 has a possible advantage. To get the same DOF that a M4/3 camera renders at f/5.6 the FF camera needs to be stopped down to f/11 -- two stops and that's two stops less exposure. Now the FF can compensate for the loss of those two stops of exposure by slowing the shutter speed -- and there's that tripod I mentioned above. Another alternative would be to raise the ISO of the FF camera but that means you're underexposing the sensor and noise is a function of exposure + sensor area so reducing exposure = more noise. This constraint I understand very well. I mostly take photos when I'm out walking and no way will I walk with a tripod. On a gloomy overcast day would a FF camera give me any IQ advantage given that I'd want the DOF and would have to keep the shutter speed hand-holdable?
So can I shoot the comparison -- these things are notoriously difficult to pull off. I have a M4/3 camera (Olympus E-PL9) with a 16mp sensor and a FF (Leica SL) with a 24mp sensor; not perfect but I can shoot the FF a little wide and crop it. I keep a 35mm lens on the FF so I first tried to just use that. But I don't have a 17mm for the M4/3 so I tried to use my zoom lens, silly me. I did a great job proving that a 35mm Zeiss prime lens is a whole lot better than an Olympus kit zoom. Try again; the crop factor between FF and M4/3 is 2 so I basically need a lens on the FF double the focal length of the lens on the M4/3. Best I could come up with was a 40mm f/2 Ultron on the M4/3 and a 75mm f/2 Apo Summicron on the FF, but that was fortuitous given the 75mm is a tad wide -- there's at least part of my compensation for the resolution difference between the two cameras. The Voigtlander lens sells for 10 times less than the Leica lens but Cosina makes respectable lenses that hold their own.
So two practical constraints then -- I want the same DOF in both photos and a hand-holdable shutter speed. (I did use a tripod for this comparison but settled on 1/40 sec as a minimum hand-holdable shutter speed. I can't hand-hold at 1/40 sec but lots of folks keep telling me they can do that and better so I compromised. In my reality as soon as my shutter speed drops below 1/150 sec I start bracketing for camera shake and experience tells me I need to do that.) I shot the M4/3 camera at f/5.6 for plenty of DOF and at 1/40 sec I was able to optimize sensor exposure at base ISO. That's important; I was able to expose the sensor to full capacity which gives me the best possible IQ from that camera. The FF camera then had to be shot at f/11 to match the DOF and at 1/40 sec. an optimum sensor exposure was off the table so I had to underexpose the sensor of the FF camera. For what it's worth here's the two photos -- both processed in C1 with noise filtering turned off and scissors on the chair the focus point. I think there's scant little difference between them and I'll leave it to you to figure out which is which.
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