You're distracted by fancy language. Instead of "photon emitter" think "light bulb." (I suppose you could think "laser pointer" instead, since that's an easier way to make all the light exactly the same color than a light bulb plus a prism.) Instead of "photon detector" think "eyeball" or "camera."
You've probably noticed that you can't detect a photon without touching it. In Star Wars and GI Joe, a laser makes a beam of light that's visible along its entire length, perhaps moving at some quick-but-visible speed. But in a real laser pointer that you buy from the store, the beam is invisible, except for a bright spot where the beam is reflected diffusely from a wall. (I was very disappointed to learn this as a kid.) In order to see the whole beam you have to pass it through a cloud of dust or water droplets. Even the bright green lasers that star-party astronomers use to point out constellations are only visible because a small fraction of the light leaves the beam and scatters backwards; that's why they're so dangerous if they get pointed at an aircraft cockpit.
You can (and should!) do a double-slit experiment yourself, by splitting a laser pointer beam with a thin staple, and sending the split beam a few meters across a room so that the interference pattern is large enough to see. You'll see a row of bright and dark spots on the wall; you can measure the dot spacing and compare it to the staple-to-wall distance and find the wavelength of the light if you want to. But there you're seeing the scattered light from the interference pattern. If you wanted to distinguish which slit the light came from, there's a very simple way to do it: walk over to the wall, where the interference pattern is, and bend down and use one eye to look back into the laser. (Of course before you did such a thing you would have gotten a class-I laser that's safe to look into!) If the bright and dark spots were larger than your pupil, then there'd be places you could stand where you would see a lot of light from the staple, and places you could stand where the staple would be dark.
And a very strange thing would happen, if you stood in the interference pattern and looked back at your slits. If you've read about telescopes, you know that a big aperture means you can resolve better than a small aperture. If you looked from the interference screen back towards your slit, and made your pupil small enough that only light from one interference fringe could reach your eye, you would at the same time make your eye's resolution so poor that you couldn't tell your slits apart any more — they'd get too blurry! And going the other way: if you made your pupil big enough that you could tell the slits apart, you'd have light from several fringes entering your eye and the brightness of the slits wouldn't change as you moved your head through the interference pattern. That's what we mean when we say that you can't both see the pattern and distinguish the slits at the same time.
Note that this is an entirely classical explanation; it doesn't get strange until the light intensity gets low enough that you observe the light photon-by-photon rather than as a continuous excitation. But the main thing is not to let yourself get confused by fancy talkers. Light bulb. Eyeball. Super simple stuff.