Filters and Holders

I still get asked many questions about infrared filters so I am going to cover a few points here.  The Canon camera is a Single Lens Reflex, which means you view directly through the lens, not a viewfinder, so when you put a nearly black infrared filter in front of the lens, with the best will in the world, you cannot see a thing through it. You can use screw on filters but I don’t recommend it. You will need to have the camera mounted on a stand and if you keep taking the filter off to view the target, then screwing it back on again to take the shot, not only is it a real pain but sooner or later you are likely to cross-thread the coupling and have to replace the lens and the filter. 

I do recommend the Cokin type square filter holder (above), you only have to screw it on once and you can slide the filter in and out at will. Simples! It is not necessary to buy a Cokin brand holder, there are plenty of low-priced copies available, that are perfectly adequate for our purposes, such as the Polaroid one above, which you can buy on Amazon.co.uk for £3.99 http://amzn.to/2r6M79y  You will also need an adapter ring to fit the holder securely to the camera lens. The Canon kit lens is 58mm diameter.

The holder has four slots. The slot against the lens is designed to take the round filter and this position will probably only work with a very large target, if at all, as we need a light and air gap between the lens and IR filter.

The remaining three slots are designed for square filters. P size IR square filters are no longer manufactured by Cokin because, they say, unwanted reflections occur if the filter is not against the lens. Suitable square filters may be available from other manufacturers or available in sheet form that can be cut up into squares..

If you have a round filter then it is desirable to trim two flats opposite each other so the filter will slide comfortably into the ‘square’ slots. I advise putting the filter in the centre ‘square’ slot.

You can buy this Cokin filter at amazon

You can increase sensitivity to capturing auras by moving the filter forwards away from the lens but this may cause unwanted reflections. Conversely you can reduce sensitivity and unwanted reflections by moving the filter backwards, towards the lens.

The round filter has a ‘squashed top-hat’ profile so you have a couple of extra options for changing sensitivity as it can be fitted two ways into the slots furthest from the lens.

For compact cameras, Cokin make a filter holder that screw fits onto the camera’s tripod mounting. The holder takes an A size (67mm) square filter. Cokin still manufacture an A007 square infrared filter but compact cameras like the Olympus tend to need a higher rating than Cokin’s 720nm. The solution is to buy 800nm – 950nm sheet and cut it to fit.

You can get the compact camera filter holder from Amazon Here