Hi tech IR blocking filter determination

Ok - so you have a bunch of filters in your astro-arsenal. How do you know which, if any, are IR-blocking? This is useful if you want to take filtered images.

Here's the definitive method, posted on the Meade DSI board:

"Hold the filter in front of your television remote's emitter and try to change the channel. If the channel changes, it's not IR blocking. If the channel doesn't change, it's a blocking filter"

Now, at first you might think that's totally mad - and it might be for all I know (though the source of the method has impeccable imaging credentials). But on reflection, that is such a neat and cool method!

I can see you all rushing off to the telly now. And I will tomorrow

Cheers

Dave

LOL ... that is such a cool bit of lateral thinking!

"Hold the filter in front of your television remote's emitter and try to change the channel. If the channel changes, it's not IR blocking. If the channel doesn't change, it's a blocking filter"

Unless your remote is too bright or wide a band...

For those with cameras that can see in IR, my Canon G3 could as can by toucam pro (obviously since we buy the filters to put on these), not sure about the 350D... turn the lights off and take a picture of your remote control while pressing some buttons. You should end up with a light source coming from the remote on the image. Repeat with the filter in front of the remote. Compare and contrast, with a bit of calibration you could properly measure all your filters.

I found this out the hard way. The canon G3 has an infrared remote control, so while watching the persieds a couple of years ago I used it to take the images. Even though it can only take 15 second images, you might get lucky. anyway, when I got home and checked the images I noticed a strange white line in many images. What had happend was that the IR remote had opend the shutter, but I hadnt heard it, so I would wave the remote near the camera pressing the shutter button until the shutter opened. Or rather closed, with 15 seconds of me waving what looks like a white led about!

Cheers,
~Al