DxOmark -- why "only" 71 points?

Started Sep 24, 2012 | Discussions thread
iano
Senior MemberPosts: 1,260
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the two comparisons
In reply to Anders W, Sep 25, 2012

There is some validity to both approaches, and I suggest which approach is appropriate depends on your priorities.

m43 could be used in one of two ways.
Option 1.

Capture the same total number of photons as 35mm FF and simply focus them on a smaller sensor. The has the challenge of 'well depth' in a smaller pixel but could potentially deliver identical performance with a smaller sensor. The negative of this approach is while lenses may be shorter as a wider angle is needed to focus a smaller frame, the front element a purpose designed the lens must the same size as FF or in practical application perhaps even larger than an equivalent 35mm FF lens. Even more significantly, in the absence of purpose designed lenses focusing all the required photons on an m43 image circle, the only choice is to use lenses actually producing a larger image circle and crop the image. The means HUGE lenses!!!

Option 2.

Capture the same photons per unit area on the smaller area and trade the reduced performance against size savings.

The consequence is that without sufficient purpose designed lenses producing an m43 image circle, option 1 in reality means a system with bigger lenses to produce the same result. Over time, option 1 could become practical if the intent is there. This would result is system with minor size savings when 'very photon counts', and the size savings we see today in most situations.

In reality, as technology improves the situations where every photon counts get rarer and rarer. I saw a report that the best m43 sensors match the best 35mm FF sensors of 5 years ago. How often are the best 35mm FF systems inadequate today? On current trends, m43 will match that within 5 years and it could take 5 years of new lens releases to deliver a system where direct competition with 35mm FF is practical.

So I suggest we live with option 2. It does mean a system where you accept the trade-offs vs 35mm full frame and balance those tradeoffs against the size saving. The alternative is to carry a system which is actually larger than 35mm FF...but delivers all the image quality. Personally I wish the lenses to make option 1 practical right now existed.

Anders W wrote:

seachicken2000 wrote:

Anders W wrote:

losangeles wrote:

Why are the m43 sensors 20+ points behind the best sensors like the D600? Is it because the pixels on a FF sensor are larger and can be manufactured to have better dynamic range? Or does Nikon simply make better sensors than Sony/Olympus?

The primary reason is that an FF sensor has about four times the area of an MFT sensor. It therefore accumulates more light (more photons) at the same exposure (same f-stop and shutter speed).

Personally, I would prefer to compare at the same photometric exposure; in other words the case where both sensors are recording the same image.

I agree that that's an interesting comparisons, though not the only interesting one.

Well said....so I have tried to explore where each comparison is most useful

However, my ambition here was simply to help the OP understand why the best FF sensors are 20+ points ahead of the best MFT sensor in terms of DxO ratings, and for this purpose, I think the answer I gave is correct and to the point. I didn't say that the 20+ difference is what everyone should use as the primary basis for choosing a camera, let alone the only basis.

I agree with your answer.

I'm in the camp that believes a 25mm f/1.4 lens on m4/3 is effectively the same as a 50mm f/2.8 lens on full-frame.

So am I, as far as DoF, diffraction, and light accumulation (but not exposure) is concerned.

Yes it is at least closest on all these counts, although not an exact match. ..And in the cases where such a lens exists m43 could use such a lens and if measured with this as equivalence possibly match 35mm FF. However, the required equivalence lenses rarely do exist in native m43 and to use a lens with a larger image circle means a BIG lens. So this equivalend is most often not practical and, since much of the m43 market is about trading some ultimate photon capture for portability, does not represent the real world equivalence for most users. I think it would be great to do both equivalence test...if the lenses were available. This would show the choice.

When using these lenses at their equivalent f-stops, the m4/3 lens will be creating a 2-stop brighter image on the sensor, and therefore the ISO will need to be lowered 2 stops to correctly record the same image.

Agreed.

Again agreed. 2 stops brighter on a smaller area would result in the same photons.

So in this case you'd need to shift the E-M5 curves to the right about 2 stops when comparing to full frame, and it's a fair fight. Comparing at the same ISO is IMO giving the E-M5 an unfair handicap.

Yes it may seem an unfair handicap. But I suggest many people are willing to trade that handicap for size and want to see the measure of what this handicap delivers.

Of course it would be better to have the 'of course if there is a suitable lens you could also move to the 'big lens equivalence with 2 more f stops and get this result'.

When shooting at higher ISOs and DoF is in short supply, I would agree. In this case, the MFT camera might even beat an FF camera as I showed here:

http://forums.dpreview.com/forums/read.asp?forum=1041&message=42531043

In other cases, such as when light is abundant (and there is no lower ISO or greater aperture for the MFT camera to go to) and when DoF is not in short supply or even undesirable, it's another story.

Well said. There are two situations. Most people will experience the size trade-off. But it would be good to do both comparisons to show what could be done when every photon counts if the right lens is available.

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