Focusing considerations
As discussed in the previous chapters infrared light focuses differently than visible light and therefore there is a shift in focus in IR and this shift varies depending on the lens being used and also on the location in the zoom range.
You have three options on how to focus your infrared camera.
- Have us calibrate your camera to the visible spectrum so you can use the existing IR focus marks on your lenses to manually correct the focus in each image.
- Have us calibrate your camera to the lens you plan on using the most. Currently this is the most popular option but does have its limitations. If the lens you send is a zoom lens then we can only calibrate the lens to a certain focal length, by default this is the widest end of the lens. There is a good chance that the focus will be off when you zoom in. Also, say the lens you sent in required quite a bit of focus shift correction and then later you decide to use a different lens. One that happens to need less focus shift correction. Well, if you try focusing at infinity you may find that your shot is blurry. This happens because this other lens requires lens shift correction but we internally calibrated for more shift.
- Many newer DSLR cameras now come with the Live View feature, some even have the ability to autofocus in the Live View mode. This opens up a whole new level of usability for digital infrared photography. As long as you have us calibrate your IR camera to the visible spectrum you can pretty much use any lens you like and still end up with perfectly sharp IR images.
This is possible because autofocus in Live View happens through the imaging sensor and as long as the direct focusing method is employed by the camera then what the sensor sees is what you get. This method of autofocus is considerably slower than conventional autofocusing through a dedicated autofocus sensor but still much faster than manual IR shift correction and definitely better than out of focus images.
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