Half Dome and the High Sierra from Mount Hamilton, Santa Clara County, California.

            An image I've been itching to try for years: the Sierra from Mt Hamilton in near-infrared. This mimics the image hanging in the observatory museum that was made in the 1920s using early infrared-boosted film. This is three images somewhat-poorly stitched together in Photoshop after some custom raw processing.

Using the NIR part of the spectrum is interesting because it reduces both atmospheric scattering and turbulence (refraction), both of which are wavelength-dependent in favor of using longer wavelengths. Range to Half Dome was about 120 miles / 200 km. Note the dark spots in the valley are patches of vegetation that were not visible to the eye due to haze, although it was clear enough yesterday (21 Jan 2023) to see Half Dome with the naked eye.

I used a D=80mm f/7 (F=560mm) refractor with old CCD camera that did not have the UV/IR cut filter that any normal camera must have. It still had a Bayer RGB pattern on it, but I binned the raw 12-bit data 2x2 to remove this (they do not have much real chromatic difference in this secondary lobe). The pixels are quite large (9um) so especially with binning this is very under-sampled even in 685-900nm which is why it looks so pixelated (if you're familiar with remote sensing conventions, this is around Q=0.3.) Filter was a Baader long-pass starting at 685nm; the sensor QE drops off around 900nm.

Taken in: United States / California / Mount Hamilton (show map)

Taken on: January 22, 2023

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