And my point is that for a designer, faced with marketing expectations, it is easy to have the ISO knob be a knob that does not in reality, for each click, change sensitivity (quantum efficiency perhaps) for noise.

Depending upon the architecture of the sensor, there are several ways to increase gain. However, noise is always present. So if there is less signal, the signal to noise level is likely to be poorer.

A low resolution display will mask the performance of the optics. You still get the same image with the same optics.

I think I posted it in a different thread, but as an example, some camera designers will aggregate pixels to get a higher sensitivity, and the spatial distribution of those aggregated pixels is usually 2x.

Me? I want all the gamut I can get! Low noise, high dynamic range, and lots of pixels packed really really tight together. Anything else is a compromise.

Ha ha, good rumor!

Camera manufacturers have also added algorithms for film effects, including grain, scratches, etc. About the only film effect I have not heard implemented is exposure reciprocity. And someone probably has done that, I just didn't find out about it.

It is not just the algorithms (I've written them), it is more about the desired performance of the camera system, the sensor to be used and the architecture of the sensor. It might be about how the sensor handles higher ISO settings, for example, whether it aggregates pixels to reduce noise, and increase area the area of the pixel.

Granted, today most cameras are CMOS, but just a few years ago, CCDs were much more common and they had all kinds of trades which could be made for higher sensitivities.

Also, unless you know for a fact how your camera manufacturer establishes the lowest ISO, I would not assume that it will give you the lowest noise. It might, or it may not. It is a function of how it was implemented.

It is clear from the frustrations that people have, that AUTO-ISO needs another generation of development. I for one would like to define weighting or costs for the trades of ISO/APERTURE/SHUTTER, which might also include noise considerations, and so on.

Just one final word...allot of what we see about ISO ranges is a manipulation of the camera design for the benefit of marketing.

Tony is right, and wrong. It depends upon the camera system designer, and the sensor designer.

Chris, the ringing artifacts are effectively a point spread function, similar to an MTF. The level of ringing is a quantum effect and creates a "blur." The size of that blur is more recognizable in high density sensors (such as on some dSLRs).

The point spread function (PSF) of an optical system (normally characterized on axis) is used as a quality metric of that system as it describes the input/output relationship of the optical system. Functionally, it is measured in the spatial domain, and MTF charts and other charts used to characterize system performance are used for this. Changing the aperture of a camera lens, changes the PSF, and it is normally at it's best at the lens' "sweet spot."

If one has a low resolution sensor, the optical system impulse response, which can be described by the PSF, matters less, because the sensor has less spatial resolution. In some cameras, adjacent pixels are aggregated, to create a larger pixel size. This tends to make the "blur" less apparent when looking at the aggregated pixels. However, it hasn't gone away, it is still there, it is just the sensor will not let you resolve it.

Everything is interrelated. There is a trade between resolution and dynamic range. So a camera with a lesser spatial resolution but a higher dynamic range can be perceived to perform as well as a camera with a higher spatial resolution with a lesser dynamic range. (A certain camera manufacturer lost market share over that issue, because most of the people buying cameras looked at the spatial resolution, not the color gamut. A story for a different day.)

With a suitable density (spatial resolution) imaging system, the ringing from diffraction effects can be seen near high contrast edges. I used the twigs in the trees when I looked at the OP image.

So to go back to the OP's question, there may indeed be diffraction effects which are limiting the resolving capability of the camera, but the area inside the red circle is something else. To me it looks like some kind of flare. It could be caused by many different things, but I have seen flare like that from filters, such as a UV filter, which tend to have less optimized anti-reflective coatings than the lens elements. Perhaps a lens system designer could provide suggestions as to what source might be more probable.

Very nice effect! Well done.

Chris, normally diffraction is a global artifact, not limited to one spot, like the light working it's way through the branches. My guess is that there is some flare there, or perhaps a spec of something on a UV filter or something like that.

There is a wiki on diffraction-limited systems, which while very technical, may provide some additional understanding for you. When we had customers say they wanted diffraction-limited systems, they were saying that they wanted systems optimized for the best that could be produced given various parameters.

Perhaps more to the general photography interest, there is a tutorial on diffraction at cambridgeincolour.com. There is a modeling tool where you can see what an airy disk would look like on many common cameras. Ditto for some similar demonstrations.

If you still have questions, let me know.

In hobby photography, diffraction is normally a limitation, as you know at smaller f-stops, which impacts resolving power (and therefore, image clarity).

I think a term commonly used is "airy disk."

Chris,

Normally one would see some patterning or rings around the artifact. Perhaps with some chromatic variability. It would come from interference patterns of the diffraction, which will be at different angles depending upon the wavelength.

I looked at things on a phone, not a computer monitor, but I would look at the grasses mid-picture for ringing effects.

Wow. If the road paint was just faded...

I think you have some other types of artifacts. If your spot were to be substantially diffraction influenced, I would expect some ringing around the spot.

I would do some experiments if it were my camera to better characterize what's happening.

I worked as an image scientist for Kodak for 37 years.

I had two adolescent male peacocks show up one day. The less dominant one left as they matured. I live in a rural area. After more than a year the peacock had a truck collision and died. Sure looked nice however.

He managed our winter, which is pretty brutal. He also found every mouse and snake and I had zero critter problems.

He got pretty used to us. My only complaint is that he liked hanging out on the steering wheel of my tractor.

Thanks everyone!

I have been using Gimp for about 15 years, but not much for photos. The other suggestions are great, and I will likely load several of them and try them out. Ones that were not mentioned here, I will be more likely to skip over.

Also the comments on Android are appreciated. I think tablets as very capable devices, but did not give much consideration to the fact that the bulk of the applications are written for phones, rather than large tablets. That's OK, the ideas presented will help save me time looking at things, and serve to set my expectations before I invest much time.

For general info, I pretty much shoot RAW all the time, and having packages like Darktable, lr, etc will simplify things like color balance and gamut adjustments. The machines I have are big and I have a large network with several NAS, so that is the general system view for much of my processing. I may still be able to use a tablet to get a rough cut on an image, but we will see.

Again, thanks all. More and better answers were received than I thought I might get, so this has been pleasant.

Not off track, and appreciated.