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Hot Spots and RGB Color Channels
The appearance of hot spots can be greatly influenced by how the image is post-processed. Hot spots usually are 80% in the blue channel, and so can be dealt with fairly easily by not using the blue channel or converting to grayscale or using Lightness. Shown below are the various channels; the central hot spot is quite obvious in the RGB and blue-channel images, but barely visible in the grayscale, Lightness, red, and green channels. This is your ticket to salvaging a problem image.
Below is another example of a blue channel hot spot, this time from the Canon EF 70-200mm f/4L IS USM. It’s very disappointing to see a newly-introduced lens (late 2006) show such strong hot spot problems. Mouse over/out of the image to see the red vs blue channels.
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Diglloyd Infrared Photography covers cameras and lenses for infrared photography.
The coverage explains all the issues involved in shooting for monochrome and in infrared. It is not a review of any particular camera or lens, though many examples are included.
- Monochrome vs color cameras.
- Post processing for monochrome.
- Guidance on workflow for infrared, including black and white and channel swapping for false-color images.
- How infrared renders, and why certain spectral cutoffs matter: false color vs black and white.
- Image quality issues to be on the lookout for in infrared.
- Numerous lens evaluations in infrared.
View an overview of infrared as well as filter spectral transmission plus examples from an optimal lens.
Canon 5D-IR + Canon EF 70-200 f/4L IS USM @ f/16, blue channel
mouse over image to see the red channel