Sorry, I was a little unclear about what I meant by "native" resolution. I was referring more to the input resolution than the output resolution, which of course are different things.
Output resolution is measured in DPI, i.e. a printer has an output resolution of say 1440, or 2880, or 5760 dpi, which relates to ink dots.
Input resolution is measure in PPI, which is of course pixels per inch. The two are often used interchangeably which is not technically correct.
The "native" resolution I was referring to was the
driver resolution, something many people are not aware of which leads to a some common misconceptions. Printer drivers are essentially a RIP, they convert the pixels to ink dots, with what is termed a "screening" algorithm. Screening algorithms are complex things, with dithering and dot gain and many other things to be taken into consideration. To write a driver with a screening algorithm which worked from
any arbitrary input resolution would be prohibitively expensive and time consuming for manufacturers who are focused on speed to market and profit, so they don't, they work from one or two fixed resolutions. These are the driver's "native" resolutions. For example, my old Epson 2100 had two native resolutions, if I printed at 2880dpi, the internal resolution is 720ppi. If I printed at any other resolution, it is 360ppi. I believe the more modern Epsons ( 5760dpi ) all use 720ppi, and Canon printers 600ppi.
What a printer driver does, when it receives an image which is
not in it's native resolution, is to immediately interpolate it so that it
IS in the correct resolution. Then it will feed it through the screening algorithm.
Knowing that the driver does this, is the key, as this allows you to perform this interpolation yourself, with a method of your choosing, rather than let the driver do it with a method almost certainly optimised for speed rather than quality. I understand a lot of drivers use "nearest neighbour" to interpolate. By doing it yourself with Photoshop and Bicubic or Lanczos, or a plugin like Genuine Fractals, you can move the emphasis to quality. This also allows you to do any print sharpening at the actual print resolution, rather than have that sharpening muddied by interpolation in the driver.
You will often hear people say that they have printed something at say 300ppi, and again at 360ppi, and they can't really see any difference. Now you know why, because they were in fact
both printed at 360ppi ( or whatever the driver's native resolution is ). The only difference they're seeing is interpolation artefacting from the different methods. This is confirmed by talks with Epson's staff and other developers, and the developer manuals for some of these printers. I've only really looked into this for Epson printers since that's what I use, I've not looked into the Canon and HP ones much, I'm not very keen on them personally.
Another misconception is in working out a relation to ppi-dpi. A common mistake is to divide the number of inks by the dpi, to work out the ppi. e.g. 1440dpi % 6inks = 240ppi. That's exactly what I did when I first started in digital printing, but apparently isn't right. This assumes the printer lays down the ink dots in a line, which is often not the case. The Epson 2100 for example ( and other similar printers ) uses a 4/2 grid of dots for each pixel.
I'm sure many of you knew this, and I don't mean to teach anyone to suck eggs, but I thought it might be of interest to some.
Is it nit-picking? Can you really see that much difference? You be the judge! Now you know, you can do your own tests.
For me personally, interpolating the image for printing is no big problem, so I always do it. It doesn't cost any more, it won't use more ink, it puts pretty much the same number of ink dots on the paper, it just means that less of them were "invented" by an algorithm and means I fed the printer as much information as it can take, and have the optimum output quality. I consider the term "fine art" to mean that every part of the process has been controlled to produce the best result, nothing left to chance, and that's what I'm going to aim for. Maybe I won't hit it, but I'll learn about all this stuff along the way, and that's a big part of it for me, I enjoy this stuff, sad as that may seem
Actually, all this techo babbly has probably made Paul even more apprehensive about digital printing... sorry Paul! It's really not that bad, there's plenty of help available, and having the ability to make prints yourself on demand that are repeatable and consistent, is a very nice ability.
I regularly have to downscale my images to fit on an A2 page 
If you have the ability to provide the printer with 720ppi of original data, that's better than having the driver invent it for you.
. I'll report my findings later.