At the outset let us make it clear, this is not a run of the mill filter, this is quite different!
As it says in the title, this is a clip filter. It fits inside your camera, just in front of the mirror to be precise.
All composition, focusing and exposure are performed in Live View. More about this later.
So what is an infrared filter? Simple answer is a filter that passes infra red light. In the case of this particular filter, from the 590nm (very red) wavelength and above.
This is where it starts getting complicated! All digital cameras are fitted with what is called a hot filter. This is a filter designed to block low end infrared (590nm) and ultra violet light, preventing it from reaching the sensor, resulting in a colour cast.
As with all STC clip filters, this one comes in a very sturdy grey plastic case, with a foam insert shaped to hold the filter.
The actual filter is made from imported Japanese Infrared absorbing glass (this leads to less internal reflection), multi coated on both sides, impact resistant, ultra thin, manufactured to extremely tight tolerances and with an A2 stainless steel (virtually non magnetic) matt black surround.
According to the STC website, this filter is currently available to fit Canon FF, Canon APS-C, Nikon FF and Sony FF cameras.
This proved to be quite interesting!
Once we had fitted the filter to our Nikon FX camera, the next stage was to create a custom white balance. We discovered two things, firstly how strong the inbuilt hot filter is; it blocked most of the infra red light, resulting in an overall red image, and secondly with a Nikon DSLR it is not possible to create a custom white balance in Live View.
We consulted with STC and also our friendly local camera repairer and converter of infrared cameras (Protech Repairs). They both confirmed what we suspected, the only way to obtain a true infrared image would be to remove the hot filter. As chance would have it, we got our hands on a converted camera. So that we could test the STC clip filter.
Fitting the filter requires the following steps: Remove the lens, switch the camera into live view, put the filter into the throat of the camera, replace the lens, then switch the camera back into live view.
Focusing is performed in manual mode as there is the usual shift in focus when photographing in infrared. A very useful accessory to have is a screen magnifier, as used in combination with the inbuilt magnification system it makes focusing the image so much easier.
‘M’ attaching screen magnifier
We started with some tests at Pevensey Castle, our initial aim being to see how sharp and even the filter was from left to right. Our second tests were on the beach, where we were looking for over all sharpness at infinity.
Full colour control image
Outer section straight from camera. Inset with custom white balance.
Pier control image
With STC 590nm filter
As we have come to expect from STC this is another first class filter, with high quality construction, zero distortion, even colour and giving sharp images. Once again we were highly impressed.
The output from the camera produces an image with sepia coloured sky, light green (but unnatural) foliage and neutral clouds. Now the opportunity arises to get creative, converting to monochrome and channel swapping, to name but two techniques.
Channel swapped and colour enhancement
For optimum results a camera with the hot filter removed is a must.
The beauty of the clip filter is that because it fits inside the camera there is no restriction on choice of lens used. Some lenses are not equipped with a filter ring, so this filter is a major plus. Also, since STC produce a range of infrared filters, the creative opportunities are endless.
We prefer to use wide and ultra wide angle lenses for infra red work.
As a result the filter worked extremely well for us and we even pushed the boundaries! STC recommend using lenses no wider than 14mm, but we used a 12mm lens, just to see if there was any cut off. Again, great results and no dark corners.
This is another filter to add to our armoury!
Our thanks go to STC Optics for the chance to test another of their superb filters, also thanks to Protech Repairs for their wealth of technical knowledge and loan of test equipment.
Source: GCM Photographic (http://gcmphotographic.com/?p=1143)