Andry the Stargazer

Are there abreviations for Achromatic and Apochromatic apart from Achro and Apochro?

On 11/07/2023 at 05:57, michael.h.f.wilkinson said:

Clouds block all wavelengths except the really long ones (i.e. radio waves)

Oh. Well then, good thing I haven't started trying yet!

23 hours ago, michael.h.f.wilkinson said:

Near infrared is possible however, and the atmosphere is fairly transparent in a number of bands (e.g., the one around 10 micron)

Good to know, that's nice! I'm actually thinking of maybe trying to make a cloud filter, by identifying what bands clouds absorb less or just don't, and extracting those to give at least some vision through the cloud. Might not work but who knows?

On 07/07/2023 at 16:00, gajjer said:

The wavelength of a 2.4GHz WiFi signal is 12.5cm. The wavelength of green light is around 550nm. The pixel size for a digital camera will be around 5um. The sensor size has to be bigger than the wavelength you are trying to detect. So it works for light but not for radio waves and WiFi is at the top end of the radio frequency spectrum. You also have to consider that focusing radio waves is done differently to focusing light.

Hope that helps.

gaj

Thanks!

On 07/07/2023 at 15:56, michael.h.f.wilkinson said:

Radio waves require very different apertures and detectors compared to visible light. In the visible spectrum, individual photons have enough energy to general electron-hole pairs in semiconductors, which then can be accumulated and detected (this is how CCDs and the like work). In radio frequencies, each photon carries far too little energy for this process, so no "radio CCD"could be built. Furthermore, to resolve anything, the aperture of the telescope needs to be much larger, as the resolution depends on the ratio of wavelength to aperture

Thanks, that helps explain it. Also, you'd probably end up with a similar problem to Infrared: Too much outside exposure! Wifi towers are everywhere now, and a mobile device or TV in your neighbours house will blot out everything anyway right? Infrared cameras have to see through the heat of everything radiating. Not easy either. That's why those are in space.

Does anyone know if a camera that picks up on radio waves exists for amateur telescopes? If not, why?