>My advice is to make three 8x10 or 8x12 prints from the same >image. That image should be shot from a tripod, if possible, >or otherwise selected by careful pixel peeping to make sure it >delivers all the resolution you think your camera is capable >of. Don't crop it except to aspect ratio if you do 8x10's. >
Neil, I sort of did part of your suggested experiment, although I used PPI settings that were evenly divisible into my inkjets DPI (that’s a topic for a whole other lengthy discussion). That was in my inane days of searching for my inkjets native PPI. I am now convinced that output devices really only print dots not pixels, although in some cases the dots can be directly related to pixels (dye-sub and traditional laser based wet processed prints).
And as you, I am age appropriately close focus challenged (limited to no closer than 15 inches with my cheaters on).
As you said, I chose a print with what I determined would be sufficient detail that was shot using a tri-pod and remote release. I made four 8.5x11 prints at 300, 240, 150 and 120PPI. What I found was rather surprising. The lighting conditions greatly affected my impression of fine detail viewable.
I first viewed the prints under a 100 watt incandescent bulb inside a frosted globe that was over my dining room table. Under that condition I reliably picked the 150 PPI print as providing the most detail, with the 300 and 240 PPI print a close second and third. That and other further testing led me to believe that my inkjets native color photographic resolution was around 140PPI. But when I went to scan the prints to see if I could use them as a sample in a discussion in another forum, I was floored to see that 100% crops showed the 300PPI print as containing more detail (which led to further experimentation).
So I then took the prints outside and viewed them in both direct sunlight and open shade. I then with regularity picked the 300 PPI print as the most detailed, with the 150 and 240 PPI prints a close second and third.
No matter what the viewing conditions, I was always reliably able to choose the 120 PPI print as the lowest detailed print. It was then that I stopped worrying about what PPI the print was when sending to my inkjet for printing, and just cropped and printed whatever it came out to. I originally made that test using my D80 images which would peak at 304 PPI at that print size. I want to repeat the test now that I have a D7000 and can provide greater PPI settings, but have not had the time nor desire to do so as of yet.
I know this probably raises more questions than answers, and can cause an ensuing hot debate. But I hope others may find my experiences and opinions helpful.