If I shine a laser through, does it really focus on the sighted spot? Does the coating on the telescope not filter IR? I thought most did maybe not. Could I shine a flashlight through and illuminate the room? How is that not the same?
2. Maybe! Cheap ones might not even have a coating.
3. You can do this! See (1) for how much brightness you can expect.
If it worked, it’s due to televisions having a relatively low activation threshold for user comfort, so you don’t have to aim the remote accurately, or often at all! Often secondary or even tertiary (or more) IR reflections will trigger television functions. For a quick sample, try aiming your remote at the opposite wall and seeing if the tv turns on. I don’t doubt this story, but I also believe it would have worked merely by pointing the remote at the TV, telescope or no.
But first make sure it isn't radio controlled. The remotes at my old house were all assigned a cable box and you could control that box with its remote from anywhere in the house.
> But first make sure it isn't radio controlled.
Based on my experience, this isn't actually a problem for people interested in trying it with their TV as RF remotes included with STBs, streaming sticks, etc., still have IR transmitters built in to control the TV.
Specifically, the actual device (e.g. cable box) is controlled with RF signals (often bluetooth) but the power and volume buttons are often controlled via IR because those are functions of the TV and most TVs have IR receivers. TV power/volume can also be conttolled via HDMI-CEC in theory, but in practice I've run into compatibility issues more often than not that way whereas doing it over IR just works.
> All refractive optics require IR filters.
The reason seems to be it prevents "bloating" of bright points of light - eg stars, and increases contrast in the visible range by cutting off UV and IR (which CCDs are apparently sensitive to), so it is in fact desirable to have IR filtered out.
Now, does that mean it's default? Maybe not.
IR filters are generally pretty effective too, so just having one anywhere will do the trick unless you're dealing with a lot of light. Cameras which would be undesirably sensitive to IR would usually have the filter built in, basically right on top of the sensor. No need for added coatings on the telescope itself.