How much IR cut?

[astromerlin]

Hi, I have been busy trying to clean the dust bunnies from my SPC900 sensor and I replaced my IR filter back onto the nose piece and thought I'd give it a test. I have several remote controls laying about so I pointed each one at the webcam to see if any of the IR passed through. I was quite suprised to see the capture image light up as I pressed the buttons on the remotes.

So, I unscrewed the filter to see if there was a difference and by an average guess I'd say my filter is reducing the IR from the remotes by about half.

Question is, I was expecting the filter to stop all the IR. Is this usual or do I have a duff filter?

[Merlin66]

The UV-IR filters I have from Baader show a very definate cut-off ( like a vertical drop:eek:) at 400nm and 700nm.

You can see this most clearly when you take a spectrum with the filter in place....you can almost use the ends of the spectrum for calibration!!

I don't know what the NIR wavelength of a remote control is, so don't know where it would be lying.

[astromerlin]

Hi, Thanks for the info, being that I aquired the filter with the webcam and it has no make or markings my best bet is to purchase a new one and use this one for keeping the dust out of my guideing webcam.