Reading resolution charts comparing MFT lenses to FX lenses

Started Mar 29, 2013 | Questions thread
Anders W
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Re: Reading resolution charts comparing MFT lenses to FX lenses
In reply to KenBalbari, Mar 30, 2013

KenBalbari wrote:

Anders W wrote:

If the pixel count of the sensors is the same, and the impact of the AA filter comparable, they have the same resolution irrespective of sensor size.

Generally, in theory, if there is no limit to available light. In practice though, it seems noise really is what often ends up limiting resolution.

There are plenty of 16MP cameras for example using a 1/2.5" sensor.  Even in tests with controlled studio lighting, they tend to not resolve as well as larger sensor 16MP models. DPR hasn't reviewed that many of these, but if you look at the ones they have, you invariable see in the comments, for example for the Nikon S9300 :


  • Noisy and soft photos have noticeable detail loss, even at base ISO of 125

and for the Sony HX20V :


  • Lots of detail smudging, even at ISO 100

or the TX10 :


With the TX10, there is definitely evidence of strong noise reduction at all ISO sensitivities with images even at ISO 100 exhibiting a slightly 'plastic' look when examined closely.


Of course, the reason these cameras are smudging detail even at low ISO is because noise is a problem for them even at low ISO.  If what you want to compare is different cameras, sensors, or formats, technically it's generally noise which is the limiting factor for resolution.

If you start comparing with small-sensor compacts, then it is obvious that MFT and larger sensors do better for resolution. But how do you distinguish between the possible reasons and single out noise (or noise reduction) as the culprit? There are also potential differences in lens performance and the impact of diffraction (much stronger for small-sensor compacts when shot at the same f-stop) to be reckoned with. Not saying that noise is irrelevant when you start comparing with small-sensor compacts, only that your claim is stronger than the evidence at our disposal permits.

And when it comes to comparing current MFT with current FF equipment in base-ISO shooting, I find no reason at all to think that noise appreciably hampers the MTF performance of the MFT equipment.

This can also be seen in DxO's "perceptual megapixels" measure.  It is apparent there that sensor size usually has more impact on resolution than the actual number of megapixels, so long as you are comparing sensors of near the same generation.  On the 10MP Nikon V1, for example, the four Nikon "one" system lenses all test at from 3-6 P-MPix.  Meanwhile, even on the much older Olympus E410, E510, and E3, also at 10MP, the 14-42 kit lens delivered 5 P-MPix.  So the modern Nikon "one" is barely matching the resolution available from a 4/3 sensor from 2007. But on modern m4/3 bodies with 12MP and 16MP, some similar 14-42 kit lenses are still only delivering 5 P-MPix.  Comparing other lenses going from older Panasonic 12MP bodies to newer 16MP bodies, tested with the same lenses, there are small gains.  The same lens might go from 7 to 8, or 8 to 9 P-MPix.

There seems to me to be more gain in moving to an equally current full frame sensor, even with no increase in megapixels.  The Nikon D4 for example, also with 16MP, has numerous lenses delivering 13-14 P-MPix, when the very best lenses on the GH2 or F1X are at 9-10 P-MPix.

Hmm. If you or anyone else can tell me how DxO defines and measures P-MPix (on a technical level, I know how they try to explain it in layman terms), we can discuss the matter further. At present, the DxO P-MPix measure is just mumbo-jumbo to me.

So it seems to me megapixels and sensor size both matter.  But for the OP's original question, are the FX lenses generally sharper.  The answer is no.   The sensor is larger.  And larger sensors are generally sharper.  It's possible for sensor design decisions to trade resolution for other advantages (dynamic range, color depth, etc.) but it would take some pretty unusual decisions (or maybe using technology that is 5-years older) to produce a full frame sensor that doesn't provide higher resolution than a 4/3 sensor.

As pointed out above, I don't think reasoning on the basis of such general principles tells us much about the way current MFT equipment compares with FF as far as MTF values are concerned. If FF sensors do better, it is because they have more pixels. But even when you start comparing MFT 16 MP cameras with the 36 MP D800, the difference is rather marginal. For example, the 20/1.7 on an E-M5 manages 1050/875 at f/2.8 on an E-M5 versus 1073/889 for the 50/1.4G at f/5.6 on a D800.

Sources:

http://www.lensrentals.com/blog/2012/03/d800-lens-selection

http://www.lensrentals.com/blog/2012/05/wide-angle-micro-43-imatest-results

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