Checking your filter
If you have acquired a filter and would like a very rough indication of its transmission threshold, the following may help.
Please note this test only applies to the Sony Handycam.
Place your camcorder in NightShot mode making sure the NightShot illuminators are on. You should see two glowing red LEDs through the front of your camera. Although they are emitting very bright infrared, they only appear to glow a fairly dim red colour to the human eye.
Whilst looking directly at the LEDs, place your filter over them and observe how much dimmer they appear.
With a 730nm filter, they are no dimmer than without.
With a 780nm filter, they are only slightly dimmer through the filter.
With an 850nm filter, the LEDs appear about half as bright as they did previously.
With a 900nm filter, the LEDs are very dim - barely visible.
With a 1000nm filter they are not visible at all.
Perform this test in daylight, such as an average room illuminated by daylight through a window or a bright bulb. If you perform the test in dim lighting or direct sunlight you will get false results.
I realise this is a very crude and simple check, but the equipment and facilities to actually measure the filter's transmission at exact wavelengths are unavailable to most people. If you have such facilities you are probably in a better position than anyone to acquire an infrared filter.
Generally speaking, a branded filter like a Hoya or B&W will have the transmission figures available on the packaging or web sites.
Do not attempt to judge your filter by looking at the sun through it! The sun is a powerful source of infrared light, which will enter your eyes completely unchecked and could cause damage!