PIXELS are just numbers in files. They have no physical size! What you are obviously referring to is the size of the individual sensels — the millions of color-filtered, monochrome devices on the sensors that convert photons to electrons.

To create a pixel, those electrons are amplified, then digitized, then (if we’re making JPEGs in-Camera), they are matrixed with many adjacent sensel values to create a series of red, green, and blue values that we call a pixel. The raw, digitized data may also be saved in a file for later processing. In any event, it’s important to know that each pixel is created from several to many sensels.

The distinction is important for understanding digital imaging. DOTS and SENSELS have size. Scanners divide up each scanned line into cells called dots. Printers represent pixels with many dots. Monitors use red, green, and blue phosphor dots to display pixels.

Pixels can be displayed or printed at practically any size.

Like everything else in life, deciding on sensor size, MegaPixel count, and how much money to spend becomes a compromise.

A larger sensor (full frame 24x36 vs a crop) let's you have either larger photo cells, or a greater number of smaller photo cells. A larger photo cells will gather more light than a smaller photo cells. This usually results in greater dynamic color range and less electronically produced noise. You get a nicer picture to look at.

On the other hand, if you need to count the stripes on the a zebra that is half a mile away, the greater number of smaller photo cells will probably give you greater definition of the stripes. Looking at the two pictures you have taken, the higher MegaPixel count may not produce the nicer photo just to look at.

A few years ago I decided I did not want to carry my DSLR camera all over Disney World, so I bought a Canon SX710HS. It's small and light. Then I found that it was much better at photographing model cars, tanks, and airplanes at a contest than the bigger DSLR. It focuses closer and has much greater depth of field. It is a 20MP sensor which also let's me zoom in to look at all those little details. Not having a view finder does make it more difficult to use in bright sunlight.

OTOH, I did just buy a new "L" lens. My first. I'm beginning to see sharper images.

I don't know if I helped you understand, but I hope so.

The D90 is still in the game, with good technique and modest effort it still produces a mighty fine photo, and I still use mine. The D7xxx line does a good job (I have a 7100, but have seen results from the four versions) and can say the same of them. 24MP (well 16, 24, 24 and 21), great control and processing ability, coupled with decent lenses, they also produce a mighty fine photo, and when used with that model line, the better lenses really start to shine. They are fine examples of the evolution of the digital series of (I'll call them) prosumer cameras. I do find it interesting that Nikon went with fewer but larger sensels/pixels @ 17.85µm2vs 15.28µm2 16% larger pixel area, for thew newest version.

I like both the D90 and the D7100, and will continue to use and probably not do another upgrade for a while, I see no need at the present time, not enough to gain, w/o $$$$ pain. I'm more interested at this time in garnering more FX glass, as I love shooting through the sweet center (and ya never know when an upgrade for me might be a FF body)..

The dense sensels package (as Mr. Burkholder says) and newer processors are wonderful, and I like having one to play with. I shoot mostly <ISO400, 100 whenever possible (unless I need the ISO float for a situation), and noise has not been an issue for my viewing on 23" monitor, and I rarely print, as my printer is older and not fully up to the task (not going to please me, anyway). Yes I can see some (noise) when I really push things, but I've been concentrating on filling the frame versus crop, and producing fine RAW images to work with, like I did when I shot film for a few decades, or when shooting for $$$$.

I'm just a photo loving hobbyist these days, so primary to me is my enjoyment of a nearly life long hobby (since my teens), and exploration of new technique, newer equipment (as budget allows), old dog learning new tricks, and trying to help those where I think I can contribute something to the fray. Another $.02.......

I have taken several photos in low light conditions and in several cases have gotten really nice, noiseless photos. If I remember correctly, the really dim light in the Hogwarts Castle at Universal did give me fits, partially because the line was in constant motion, and I did not have time to try different settings before the line moved and all light conditions changed. On the other hand, going through Star Tours on a slower day, I held the little bugger down over the railings and got really good photos of the stuff under the walkways that most people never see.

If you want I can post a few photos I have taken with it. Just let me know.

If it's not too much trouble. But only if they are at the "high-high" ISO in that range 10,000-12,000. "Lower-high" ISO around 6,000-8,000 is lower than where I shoot. I have noticed that there is a disparity in the scale when some folks refer to "high" ISO values. I wish that we UHH'ers could adopt a policy of using the ISO numbers when they say "high". Some folks call 3200 or 6400 "high"....If your ISO values were not these "ultra-high" numbers, then you don't need to post the images. Thanks

High is entirely relative to the medium. 12,800 is unusably high for most sensors smaller than full frame. But some full frame sensors can be used there quite acceptably. 12,800 is ridiculously high for film, which tops out two stops slower at around 3200 (Ilford Delta 3200 B&W negative film).

*Rough* format equivalent ISOs *for noise, dynamic range, and color depth in low light*:

Full frame/FX: 12,800 (crop factor 1)
APS-C/DX: 6400 (crop factor 1.5/1.6)
Micro 4/3: 3200 (crop factor 2)
1": 1600 (crop factor 2.7)

Of course, exact equivalency isn't really possible, but setting these types of cameras to these speeds will yield images that look somewhat similar at similar megapixel counts, crops, and angles of view.

This is why vibration reduction and image stabilization technologies (and MetaBones SpeedBoosters) are so useful in Micro 4/3 cameras.

If it's not too much trouble. But only if they are at the "high-high" ISO in that range 10,000-12,000. "Lower-high" ISO around 6,000-8,000 is lower than where I shoot. I have noticed that there is a disparity in the scale when some folks refer to "high" ISO values. I wish that we UHH'ers could adopt a policy of using the ISO numbers when they say "high". Some folks call 3200 or 6400 "high"....If your ISO values were not these "ultra-high" numbers, then you don't need to post the images. Thanks

My response will exceed the range of the question. Read on , McDuff!!

Assume that your sensor is a brick patio of say 10 ft by 10 ft. We'll call that size a full frame patio. If it's made with big bricks (pixels) it takes less bricks to complete the 100 sq ft area. (OR more bricks if smaller bricks are used). If the bricks are different colors, a picture (mosaic) can be made by the bricklayer craftsman/artist. In this analogy the area of patio is the sensor size and the number of bricks is the megapixel "size". The patios come in only 3 or 4 different standardized sizes (Lets call those sizes Full frame, APSC crop, 1 inch and 4/3 ). The number of bricks determines how much detail it is possible to show regardless of what physical size the mosaic is. For given number of pixels, large pixels yield a larger sensor and smaller pixels mean a smaller sensor. Whether larger sensor size equates to greater sharpness (under ideal conditions) is open to debate. It just means that the pixels can be larger. Larger pixels can, but must not necessarily, have greater dynamic range and less noise. NOTE: all current sensors that I know of in major manufacturer's cameras seem to have better dynamic range and noise characteristics from larger pixels. It is up up to the camera buying public to choose:
1. sensor size
2. within the sensor size, the number of pixels that will yield, for their chosen type of photography, the best compromise between number of pixels and pixel size ie max obtainable detail vs dynamic range and noise.

My rant begins here!
Note that early digital cameras had few (3-6) megpixels yet produced some amazingly sharp photos. This brings into question how many pixels are really necessary and where the pixel overkill threshold lies. The current crop of multi mega mega megapixel cameras must of necessity have smaller pixels than they would if they had 1/2 the pixels in the same area of sensor. Because they have so many pixels , they can afford to throw many away through cropping without noticeably effecting the perception of sharpness in the photo. But, because they have such small pixels, they have diminished dynamic range and increased noise. Yet, sensors are arguably becoming capable of capturing more detail than the unaided human eye can perceive. Each new generation of sensor design seems to have better dynamic range and lower noise than does the previous generation at the same number of megapixels. (And at exponentially greater cost). Each of us must determine how much value we receive back from the additional dollars we must divert from our other needs or wants in order to get the latest high megapixel full frame camera body. Excess capabilities are a waste of dollars unless they are actual useful. How little can one spend in order to get a camera whose capabilities barely exceed their ability to utilize those capabilities? Where is the balance between cost and value best achieved?
BTW: I believe that dollars spent on high quality lenses return greater value than if spent on camera bodies. Good glass on a so-so consumer grade body will yield better crispness than mediocre glass on a super duper professional grade body. A good lens is a better long term investment since it will probably be used on several generations of camera bodies. Hope this helps. I also hope my (far too obvious) personal preferences have opened some new ways of looking at wise expenditures for you to consider. I also hope that you feel free to totally ignore my rant.