[Xamayon]

For #2 - Assuming it's not a spotting scope or similar, filtering IR wouldn't have much benefit. An IR filter might even hurt for the typical star gazing type usage, depending on the equipment used. Cameras for looking at things in the night sky often explicitly lack IR filters (often at massively increased cost) to increase sensitivity to any available light.

[dylan604]

Very much this. Any IR filtering on a telescope would not be a very favored option. There is so much interesting stuff to see in the IR range. To your point about lack of IR filters, there are places that offer a service to have the IR filter removed from your DSLR. You can just add an IR filter to your lens to have it back to "normal".

[jvanderbot]

This seems incorrect. Everywhere I look I hear effectively:

> 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.

[Xamayon]

Possibly desirable for optimal image quality, sure, but taking pictures is not the only use for a telescope. Many things just require knowing how much light is present, and how that changes over time. Occultations are one such case which I have familiarity with. Objects are often so faint that every little bit of light is essential to improve SNR - https://occultations.org/

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.