As loyal Pogue’s Posts readers are no doubt aware, I’ve spent the last seven weeks in TV land, filming a first batch of six episodes of my new Discovery-network series, “It’s All Geek to Me.” It was an exhilarating, exhausting, enlightening journey. Someday when we’re all together, I’ll tell you about it.

Actually, I’ll tell you about one thing right now. We did an episode on digital cameras. Part of the fun involved visiting a couple of big electronics stores, posing as somebody who didn’t know much about cameras, and, later, commenting on what they told me.

The clerks at one store recognized me. The guy at the other store had no clue that I’m a tech writer. Both of them were surprisingly frank, pointing out, for example, that five megapixels is plenty for prints up to smallish poster size.

Now, every time I write that, I hear from furious or baffled readers. “I don’t get it,” wrote one. “A ten-megapixel camera produces photos about 3640 pixels wide–enough to make a 12-inch print at 300 dpi (dots per inch) on a good printer. Sure, you can go lower, but quality is sacrificed; you can’t make an 11×14 print, let alone anything bigger.”

I have to say, the math sounds right. But I also have to say that he’s wrong.

On the show, we did a test. We blew up a photograph to 16 x 24 inches at a professional photo lab. One print had 13-megapixel resolution; one had 8; the third had 5. Same exact photo, down-rezzed twice, all three printed at the same poster size. I wanted to hang them all on a wall in Times Square and challenge passersby to see if they could tell the difference.

Even the technician at the photo lab told me that I was crazy, that there’d be a huge difference between 5 megapixels and 13.

I’m prepared to give away the punch line of this segment, because hey—the show doesn’t air till February, and you’ll have forgotten all about what you read here today, right?

Anyway, we ran the test for about 45 minutes. Dozens of people stopped to take the test; a little crowd gathered. About 95 percent of the volunteers gave up, announcing that there was no possible way to tell the difference, even when mashing their faces right up against the prints. A handful of them attempted guesses—but were wrong. Only one person correctly ranked the prints in megapixel order, although (a) she was a photography professor, and (b) I believe she just got lucky.

I’m telling you, there was NO DIFFERENCE.

This post is going to get a lot of people riled up, I know, because in THEORY, you should be able to see a difference. But you can’t.

And I’m hoping this little test can save you some bucks the next time you’re shopping for a camera.