When searching I stumbled upon a Chinese site which sells a 'Blast Furnace Top Camera' which should withstand 2000 C for long periods of time. I thought 'How do they handle this ?'. No specifications of the used material for its casing are given. What kind of unobtanium do they use ? Molybdenum ? Tungsten ? Iridium ? And the viewport window must be made of diamond as that is the only transparent material withstanding 2000 C. https://en.itvrb.com/product/159.html If this were real, then many steel plants use such cams inside their blast furmaces, EAF or other high temperature equipment. Any ideas on this ?
You could get something similar with an insulating refractory casing surrounding a water cooled housing and a pinhole aperture. There's commercial makers of optical grade fused sapphire (melts at 2072 Deg C) mainly used in thin slices for mobile phone screen protectors that could be used to grind a lens from. Silicon carbide melts at 2830 deg C and can be had as the synthetic gem Moissanite with a clear colour. Diamond will turn into graphite and burn at higher temps.
