24mp sensor for m43? 3.2micron pixel pitch!

Started May 9, 2013 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: 24mp sensor for m43 ? 3.2micron pixel pitch !

Detail Man wrote:

Anders W wrote:

Detail Man wrote:

Anders W wrote:

RicksAstro wrote:

Merak wrote:

The 24mp will reward you with a visible increase of diffraction compared to a rather small increase of resolution. With todays 16mp sensors f16 is heavily impacted by diffraction, f11 in most cases visibly impacted and f5.6 or faster with no visible impact.

With 24mp f16/f11 will almost become unusable, f8 visibly impacted and only f4 or faster with no visible impact. I don't think the majority of photogs has any interest in such a limitation....

Quite the opposite is true. When viewed at the same image magnification, the image from a higher pixel density sensor will suffer from LESS diffraction effects, more more.

Hi Rick,

We are in perfect substantive agreement about the ins and outs of pixel counts and you are doing an excellent job in this thread of helping others understand how things actually stand.

However, for the benefit of those who have a less firm grasp about these matters than you and I, I would express what you say about diffraction in a slightly different way. To sort things out fully, I think it is appropriate to use a concrete example. Suppose we are comparing the performance of the same lens on cameras with different pixel counts, as Pekka Potka recently did with a Nikkor 35/1.4G on a D800 (36 MP) versus on a D700 (12 MP),

http://www.pekkapotka.com/journal/tag/d700

If we compare at the peak aperture of the lens, say about f/5.6 as in Potka's example, the difference is going to be pretty substantial. I don't know the numbers in this particular case (Potka shows test images rather than resolution numbers) but suppose it is 1000 lp/ih (line pairs per image height) at MTF-50 (50 percent contrast) for the D800 versus 700 lp/ih for the D700.

If we stop down further, say to f/16, both cameras will lose resolution due to diffraction. Again, I don't know the exact numbers, but the resolution figures might now be something like 800 for the D800 versus 600 for the D700. Based on these numbers, the D800 would lose more than the D700: 1000 - 800 = 200 versus 700 - 600 = 100. And in this sense, it is in fact correct to say that diffraction will have a stronger impact on the camera with higher pixel count than on the one with lower. However, and that's the really important point, the D800 will still be ahead of the D700. The resolution advantage of the D800 will be smaller and smaller as you continue to stop down beyond the peak aperture, but it will still have the advantage.

And will provide more resolution from even crappy lenses than with the less dense sensor.

The Nikon forum went through this learning curve with the D800, which provided more resolution, less noise and more dynamic range than the less dense bretheren.   Finally, most people understand this now.

Those who want quicker RAW post-processing and faster frame rates do have legitimate concerns, but those claiming you need better lenses and/or can't stop down to shoot have finally faded into the woodwork.

Anders,

It seems to me that it is rather hard to generalize as to the Read Noise performance for any given individual image-sensor design. From what I have been reading, assumptions that Read Noise levels handily scale downward with photosite dimensions are to say the least just a bit glossy. Have a look at this post (as well as the prior posts and threads referenced therein):

http://www.dpreview.com/forums/post/51432240

I cannot but agree here (as I think you already know).

Well, I thought that you might. We have picked our friend bobn2's brain a number of times about that subject (of Read Noise and photosite dimensions), and he defers in the end to the cautious approach. I have found that there exists a strong desire on the parts of some to put a simple face on the matter, but my research into what Eric Fossum has and still does opine indicates otherwise. If anybody should be believed regarding such matters, I would think that it would be Eric Fossum - and he appears to indicate that there is nothing simple about these matters of sensor photosite design.

Yes, I was already aware of what Fossum has to say here and was, as you know, inclined to be a bit sceptical about simplifying the matter too much already before that.

Where it comes to diffraction effects, have a look at this post, and let me know what you think:

http://www.dpreview.com/forums/post/51382403

My modelling of composite system MTF responses indicates that smaller photosites do not result in any more spatial frequency resolution beyond the extinction spatial frequency of lens-system diffraction. They can result in a larger area under the composite system response MTF curve below that limit - but the advantages diminish fairly rapidly to what are miniscule amounts. The presence of AA filters has a secondary effect of accentuating the relative advantage of smaller photosites - but that particular effect is not present in the case of image-sensors having no AA filter assembly.

I would have to take a closer look at your work on diffraction and then think about it before daring to comment in a more definitive way. But if I understand you right, your results are in line with what I say in the post you reply to. More pixels benefits resolution but as diffraction gets increasingly strong, the resolution advantage gets smaller and smaller, eventually approaching zero. Is that correctly understood?

In the sense of spatial frequency response, when the magnitude of the composite system MTF is increased at any particular spatial frequency, one could term that as an increase in resolution.

Yes, I know it is MTF (i.e., contrast and resolution) we are talking about. I was just trying to express it in a somewhat "popular" way.

The benefits of smaller photosites arise in large part from the higher spatial sampling frequency of the smaller sized photosite sensor - which itself is a benefit over and above that of the differences which exist below the Nyquist spatial frequency of the larger size photosite sensor.

As the extinction spatial frequency of the lens-system reduces (as the Wavelength multiplied by F-Ratio product increases), the above described (Nyquist limit) advantage of smaller photosites due to higher spatial sampling frequency begins to disappear. As well, ratio of the area under the compared composite system MTF responses (below the Nyquist spatial frequency limit of the larger sized photosite sensor) also begins to diminish - to the point where the ratiometric differences approach what are practical insignificance. Thus, "more pixels equals more detail" is a bit of a "mantra" ...

Well, as long as you use apertures close to the optimum (about f/4 for fast MFT primes), there are good reasons to think that more pixels than we currently have would be an advantage, wouldn't it? Not that this is anything that I consider of primary importance but welcome nevertheless (provided there are no downsides in terms of sensor efficiency).

I also deem it likely that we will see an increase in the pixel count of MFT sensors before too long. With current sensor technology, I am not sure it makes sense to go much further than we already have. But sensor efficiency is likely to continue to improve (although perhaps rather slowly, since we are getting close to the physical limits, unless someone finds a way to get rid of the Bayer filter without any major downsides) and, above all, I hope/think, we will soon see sensors with arbitrarily low ISOs, like these

http://www.dpreview.com/news/2013/02/27/rambus-shows-binaryt-pixel-sensor-technology-for-expanded-dynamic-range

http://www.pixim.com/products-and-technology/technology

For MFT, with primes peaking at f/4 (at a DoF corresponding to f/8 on FF), ISO 25 or even lower would often be enough for shooting in ordinary daylight with ordinary FLs. And those who are now putting on ND filters to shoot their fast primes wide open in the sun at 1/4000 could instead do so at ISO 1.5 or so and 1/100. These low ISOs would hopefully come with pretty high DR values, which in turn would make significantly higher pixel counts meaningful.

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