A different approach to IR filters

I’ve had a camera converted for infrared (IR) for nearly three years now (see my IR-related posts for more information and some sample images). You don’t have to use a converted body to take IR pictures but there are some distinct advantages to doing so, perhaps the major one being that exposure times are similar to those of visible light photography. Using an unconverted body requires exposures of much longer duration – maybe 10s of seconds. In addition, depending on exactly which internal filter you have fitted during the conversion, you may not require an additional IR filter fitted to the lens.

A disadvantage is that a converted body can only be used for IR photography unless you have what’s called a full spectrum internal filter fitted, which allows IR, visible light and ultraviolet (UV) to be recorded. You can buy external filters that allow either just UV or just IR to pass, so a full spectrum conversion allows you to use these to select which light will be recorded. In addition, an external “hot-mirror” filter can be bought that allows only visible light to pass – fitting one of these cuts out the IR and UV, allowing a full spectrum camera to capture normal images. Unfortunately, hot-mirror filters tend to be quite expensive.

If you want to use a range of lenses with a converted body, you have the age-old filter problem: do I

  • buy a set of each type of filter to match the range of filter screw diameters needed by my lenses?
  • buy the largest size filter I need (and maybe a bit bigger for future-proofing) and tolerate having to use step-up rings on my smaller lenses?

The first option can be very expensive but the second option can be very inconvenient – neither is a great solution.

Enter a new range of clip-in filters from STC. These are available for a number of different manufacturers’ body types, including my own Olympus micro four-thirds bodies. Note that you have to be careful to select the correct fitting. The filters fit inside the lens mount flange – in front of the sensor – and so Olympus M43 clip-in filters won’t fit a Panasonic M43 body. Fortunately for Panasonic M43 users, the Panasonic fitting has just been added to the STC range.

After fitting a 720nm IR clip-in filter, you are now able to use any of your lenses to take IR pictures without having to fit a filter to the lens. You still can fit external filters, of course, if you want to limit IR to its longer wavelengths, for example. Alternatively, fitting a UV-IR Cut filter (this is the hot-mirror filter) lets you use the camera as a normal, visible light body.

STC provide quite a wide range of different filters for different uses including ND filters of various strengths, different IR pass bands and astronomical filters. I’ve bought a 720nm IR filter and a hot-mirror and look forward to trying them out. I’ve given them a brief test and they seem to do the job but I haven’t had any good IR weather since getting them. I’ll update this post with some pictures when I manage to take some.

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