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Recent Micro Four/Thirds sensors seem to have improved their noise performance significantly.

I own a Canon 5D Mark 2 full frame DSLR and am considering purchasing an Olympus OM-D EM5 micro four thirds camera.

I have rented the EM5 and notice the noise performance is about half a stop to a whole stop behind my 5D2.

However, the OM-D is able to take the same picture as the 5D2, at a lower ISO and the same shutter speed.

For example:

If I am shooting with the 5D2 and 50mm lens, and I take a shot with 1/60th, F/5.6, and 1600 iso. To get a comparable shot on the OM-D (same depth of field) with 25mm lens, I shoot at 1/60th of a second, F/2.8, and 400(!) iso.

Does aperture equivilence give the OM-D a clear advantage here, or am I looking at this wrong?

I understand that in a true very low light situation where I must shoot wide open (both cameras at F/1.4), ISO must be equal on both cameras and thus the 5D takes the crown again. But for moderate situations where F/1.4 is not required, is the OM-D actually better?

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4 Answers

up vote 6 down vote accepted

I think fundamentally you are looking at it a bit wrong. In theory, the aperture equivalence is exactly canceled out by the decrease in sensor area. When viewed at the same final size, the perception of noise should be about equal between your full-frame F/5.6 @ ISO 1600 and micro-four-thirds F/2.8 @ ISO 400.

But you note

I have rented the EM5 and notice the noise performance is about half a stop to a whole stop behind my 5D2.

This isn't due to an inherent advantage but simply a testament to the amazing tech in the OM-D E-M5, and the difference three or four years of sensor development makes. If you compare to the newer 5D Mk III, we'll be closer to the theoretical world, with a noise advantage of about two stops: the same as the crop factor, and therefore the same as the aperture difference.

There's a certain point in the real world, though, where performance is over the threshold in any case, and so while the smaller camera doesn't necessarily have any noise advantage, it doesn't have any meaningful disadvantage either, so you can consider other advantages (like size, weight, price, and so on).

On the other hand, you can shoot with a 50mm f/1.2 on the full-frame camera, and it's just not possible to get the equivalent 25mm f/0.6 in micro four thirds. And again, that might make a difference in the real world, or it might not. That's why we have options in the market, after all.

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There is a smaller amount of sensor to cover, so for the same size hole, there will be more light since it is less diffused compared to the surface area of a larger sensor. That comes with a lot of other costs though, for example, the more focused light will have less bokeh and a wider depth of field. It's also going to alter the mm length on lenses since it has less sensor to expand on to. The sensor itself will need to more tightly cram the pixels to be able to achieve similar resolution and may involve trade offs in design.

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As you noted, your aperture is different. f/2.8 is two stops faster than f/5.6 and ISO 400 is two stops slower than ISO 1600. So, you balanced the equation since aperture is what controls depth of field.

Basically, to get the same shallow depth of field on the OM-D, you had to shoot with the lens more wide open and that results in a lower ISO. The smaller sensor in the OM-D results in more depth of field versus a larger sensor for the same aperture, one of the reasons that camera phones and point and shoot cameras struggle to get shallow depth of field.

So, what I mean by all that, is no. It may have an advantage as a result of sensor improvements, not sure on that, but it wouldn't be because the sensor is smaller.

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I'm not entirely sure the size of the sensor versus the size of the "hole" is the correct way to look at it. some lenses wide open let in less light than others - evan at the same f/stop. i think this depends more on the type (and make) of the sensor. cmos sensors are better at low light (in general) than ccd's, but some cmos sensors are more light sensitive than others. i also think that comparing a full frame sensor against a micro four thirds sensor is an exercise that will raise more questions than answers.

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Amount of light actually let in by the lens at a given f-stop is the "t-stop". This is rarely more than a fraction of a stop — see What is a T-Stop for more. The difference in CMOS vs. CCD (or any other tech) should be encapsulated in the ISO rating, although it is true that different cameras produce a slightly different exposure for the same nominal ISO (because the standard intentionally leaves room for interpretation). Both of these cameras use CMOS, however. –  mattdm Apr 4 '13 at 14:11
    
I'm aware what T Stop is... the point i was making was that if you have two different lenses, say canon and nikon and they are both shot at f1.4, that doesn't mean that they both let exactly the same amount of light in (in fact they won't). –  stephencosh Apr 4 '13 at 14:18
    
Are you saying that that's for a reason other than the t-stop difference? (That is, something other than practical considerations due to real-world physics and lens construction?) How would this relate to the type/make of sensor? –  mattdm Apr 4 '13 at 14:20
    
not at all. just basically saying you cannot compare light sensitivity on a sensor fairly if you are using two different manufacturers lenses, in this case olympus and canon. –  stephencosh Apr 4 '13 at 14:23
    
Okay, cool. Just wanted to be sure of what you are saying. In this particular case, it happens that DxOMark has tested what are probably the two lenses in question, finding the Canon and Panasonic lenses to have t-stops of 1.6 and 1.7 respectively. (Measurable but a small factor.) –  mattdm Apr 4 '13 at 14:34
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