DSLR/Webcam IR filter

[skywest]

Something I often read but is never explained.

When modifiying a DSLR for astro, the IR filter must be removed but when modifying a webcam for astro the IR filter must be left in place.

Can anybody shed some light on this?

[Cornelius Varley]

37 minutes ago, skywest said:

Something I often read but is never explained.

When modifiying a DSLR for astro, the IR filter must be removed but when modifying a webcam for astro the IR filter must be left in place.

Can anybody shed some light on this?

For webcam imaging (planets/moon) the existing IR filter is left over the sensor or one added if the original one was part of the lens to ensure only the visible spectrum is recorded. The webcam is sensitive to the invisible IR light which would otherwise be recorded and give a pink cast to the image. IR light also focuses at a slightly different point to the visible light so would also give a slight (out of focus) blur to the image if not filtered out. DSLRs, on the other hand, have their IR filter removed so as to record a greater range of the spectrum (more red).

[michael8554]

Most modded DSLR's have the LPF2 filter removed, which extends the spectral response to give more Ha output.

But usually the LPF1 filter remains, which filters UV and IR.

MIchael

[skywest]

Thanks guys, that makes more sense now.