Setting the White Balance before you start shooting is vitally important, unless shooting RAW, where it can be adjusted in the RAW Converter. One method is to do a manual White balance pointing at green grass which has the same light falling on it as the subject. Set the White Balance everytime you change filters, but also if the light quality significantly changes.
With the Sony Nex and A7 series cameras you always get an error warning when setting a Custom White Balance, but if you just press ENTER, the camera accepts and then uses the Custom setting, even though it thinks its wrong. Basically it is saying its out of the normal range, but will grudgingly accept the custom setting!! The Colour Temperature setting for most IR work is normally the camera's minimum; 2500K.
The procedure for setting a custom White Balance on a Sony camera is;
Find White Balance in Settings, then scroll to >Set< , then point the small circle on screen to your chosen point say Green Grass and Press Enter [or Press the Shutter Release on older cameras] the camera then says WB Error, but just Press Enter and the camera accepts the reading.
Enter is the centre button of the Navigation dial!!
Filters For Full Spectrum Cameras
Assuming you are using a Full Spectrum camera, the best 2 filters to own for Infra Red are a Deep Red, such as a R25A filter which can be used for False Colour or Black and White, or a 720nm IR filter such as a R72 filter, which is mainly for Black and White. I often use the R25A when the sun is out and the R72 when its cloudy, but that is a generalistion. The R72 is easier to post process, whereas the R25A requires extensive Photoshop work to get the Gold Foliage effect, although you can do B&W's just as for a R72, but with a bit more control if required.
A R25A filter is approximately the same as a 590nm integral sensor filter , ie it blocks nearly all wavelengths of light shorter than 590nm and anything longer is allowed through. 590nm corresponds to red visible light, so the camera will see Red and Near Infra red up to the sensor's limit. Because the visible Red sensitivity of the cameras RGB sensor is maintained, the G and B sensors are sensitive to gradually longer IR wavelengths, which allows some degree of separation between the RGB channels. So if the R Channel is swapped for Blue in photoshop, and vice versa, then skies tend to come out blue and foliage comes out yellowy red or Gold with a bit of tinkering in photoshop, see below
A R72 filter is approximately the same as a 720nm integral sensor filter , ie it blocks nearly all wavelengths of light shorter than 720nm and anything longer is allowed through. 720nm is barely visible to the human eye and transmits Near Infra Red up to the sensor's limit. There is very little colour separation and so the False colours of the R25A filter are not really possible, however it does give darker richer skies and more contrast in foliage in B&W images than the R25A .
There are longer wavelength filter like 850nm and even 920nm filters which are even more dramatic then the R72, but they severely cut the sensitivity of the sensor so tend to need much longer exposures, plus most lenses with Hot Spots will likely be worse at longer wavelengths, as they are further from their design parameters.
A UV/IR Cut filter is useful to return the camera to normal visible light sensitivity, similar to the filter that was removed from the camera in the conversion process. However, because it is unlikely to be exactly the same as the factory fitted filter the colour reproduction is likely to be slightly different and Auto White Balance [AWB] and other pre selected colour settings on the camera are unlikely to be accurate. This means a custom White Balance will have to be performed again. Another problem is the IR blocking part of the filter is done by a Hot Mirror coating [Dichroic] that reflects the IR light rather than absorbing it, this causes problems with wide angle lenses wider than about 28mm in full frame terms. The effect of the filter lessens as you go away from the centre, so the corners of the image tend to be discoloured by IR light leaking through.
Clip In Filters for Sony and Canon Full Spectrum Cameras
Recently a couple of filter manufacturers have developed a new style of filter that clip into the lens mount of certain cameras rather than screwing to the front of the lens. They are only available for the Sony A7/A9 series of full frame cameras and the Canon EOS M and M3 from STC and Astronomik. They are not exactly cheap, but may actually work out more economical than buying several filters of different sizes to cover a few lenses. They do offer several advantages over lens filters, the main one being convenience as you don't have to swap filters when changing lenses especially if using a normal camera at the same time. Astronomik do a range of specialist filters for Astrophotography of which the light pollution filters will be of most interest. STC do 590nm, 720nm and 850nm IR passing filters for general IR photography, which give Full Spectrum cameras all the flexibility advantages of Full Spectrum with the convenience of a specifc wavelength conversion. STC also do a Cilp In UV/IR Cut filter which unlike ones that go on the front of the lens do not suffer from colour shifts in the corners when used with wide angle lenses, I have used lenses down to 15mm with little or no corner colour shift. STC do a range of UV/IR Cut filters with cuts at 595nm to 625nm, I use a 615nm and find that the Auto White Balance works fine and is 99% of a normal camera. Because of the ease of use and simple changing of these clip in filters it allows, for the first time, the reality of just having one camera to do UV, Visible or IR without compromise, its a real game changer!! PS. I very slightly bent with small pliers the two top lugs to make the a snugger fit on mine.
First of all if you have a Sony Mirrorless Camera, you should really be using RAW files, Sony make this easy by letting you download Capture One for Sony, by Phase One, free of charge. Adobe Lightroom the most popular Raw Converter, but does not have the colour temp range required for False Colour IR and so cannot be recommend for IR at all. Whichever converter you use it allows much more control over white balance and other variables than the Camera's .jpg's. The higher Bit Depth of the RAW Data allows much more manipulation before any unwanted artifacts, like Banding, Highlight blowing and Shadow crushing, start showing.
Capture One for Sony can be downloaded for free here; https://www.phaseone.com/en/Download-Sony.aspx
You will have to Register or Login, but there is no charge for the Sony version. The Free Sony version will only work with RAW files fom Sony Cameras, the Sony Pro Version which is chargable [ 50-60 Euro ] has a few more functions, like wired tethering with A7II series cameras and Selective Adjustments, but 90% of the normal functionality is in the free version. Please note Capture One only works on 64 Bit computers!!
Canon and Fuji have their equivalent raw converters, all of which will allow the White Balance to be adjusted on the captured RAW Data. Both of which are much more suitable than Adobe Lightroom. This link shows a way of using Lightroom via a Custom Profile;
Setting the White Balance in the Raw Converter normally gives a greater range of adjustment than the cameras own settings, Sony Cameras for example won't go lower than 2500K, but Capture One allows settings as low as about 1250K. One of the best ways to set the White balance is to use the dropper tool and select an area of the image you want to be white. I often select the brightest part of a cloud in the scene, but you can also select a bright piece of foliage. The sort of settings that are "Normal" tend to be in the range of 2000-2500K.
Once the White Balance is set, you will normally go about getting the Levels, Sharpening, lens adjustments etc. right in the normal way. If doing Black and White you may do this in the Raw converter, but I would nearly always export the file to Photoshop for either the BW Conversion or False Colour Channel Swapping and finalising the image.
Once your image is exported to Photoshop, normally as a 16Bit image, the first thing to do for False Colour work is swap the Red and Blue Channels, this will make skies appear Blueish and Foliage red to yellow tones. To do this go to IMAGE>ADJUSTMENTS>CHANNEL MIXER. You will see the Red Output Channel is selected in the top Drop down Menu and the Red Source Value is +100%, Green and Blue are 0%. Change the Red Value to 0% and the Blue Value to +100%. Then in the OUTPUT CHANNEL drop down at the top Select BLUE, then Change the RED value from 0% to +100% and the BLUE value from +100% to 0%. Click OK. Now the Red and Blue Channels have been swapped and you should have blueish skies and redish yellow folaige. You will now need to use the HUE/SATURATION control in IMAGE>ADJUSTMENTS>HUE/SATURATION to adjust the colours to taste. I normally edit the colours individually by selecting Red, Yellow or Blue in the EDIT drop down box at the top. With each colur in turn adjust the Hue Slider at the top and the Saturation Slider in the middle to taste. Don't overdo it!!
Rather than doing the False Colour Effect above you may wish to produce a Black and White image, again get the image about right in your Raw Converter and export it to Photoshop, then before doing anything else, you will need to perform:-
In Hue/Saturation, you could just move the middle slider all the way to the left to desaturate all the colours evenly, but this would be a mistake as it would not give tha opportunity adjust the grey tones for each colour or channel in the image. If you select BLUE in the EDIT box at the top, the adjust the satuartion to -100% any Blue tones will become grey, but if you now also adjust the LIGHTNESS control at the bottom, you can control the density of the Blue tones which are now Grey. I mention the Blue tones first as I have found that HOT SPOTS with certain lenses tend to only be in the Blue channel and by adjusting the Blue level's LIGHTNESS you can completely dial out the Milky Looking Hot Spot!! Once the Blue tones are done you can go on to do the Red and Yellow tones in the same way to taste. I have also found that some light fall off towards the corners of some lenses tends to be in the Red and Yellow tones, which again can be adjusted out if necessary. Finally, once the individual colours have been desaturated and adjusted for tone, select MASTER in the top box and then desaturate all the colours by moving the middle slider all the way to the left. CLICK OK and your done.In later versions of Photoshop there is a much better tool; IMAGE>ADJUSTMENTS>BLACK AND WHITE, this immediately gives a greyscale image, then you can adjust the individual tones for each "colour". Again I always start with the Blue, to dial out any hot spots.
The following images are available for download, either click the image for an unedited compressed .jpg [About 9Mb] or click the "Download .ARW Raw File" for an original out of camera Sony .ARW Compressed Raw File [ About 24Mb]. These images are available for free download for you to experiment with, please do not publish or post them elseware.
Image taken with Full Spectrum Sony A7II with Loxia 21mm f/2.8 lens set to f/6.3 at 1/160s with Hoya R72 IR Filter.
Image taken with Full Spectrum Sony A7II with Loxia 21mm f/2.8 lens set to f/6.3 at 1/320s with Hoya R72 IR Filter.
Image taken with Full Spectrum Sony a5000 with Kit lens and a Hoya R25a Red Filter at 20mm and f/7.1 at 1/250th Sec. The thumbnail on the left is the processed image, but if you click it you can download the Out of Camera jpg or click the link above for the Full .ARW Sony Raw file.
Click the Grey Button to download the original Raw File.
Click the Photo to download the full Post Processed False Colour File.