I get allot of questions concerning the infrared photos that I capture. Most of the questions I get fall back on the infrared filters being used. Which in my case is usually a filter in the 800nm+ range. I prefer a filter that cuts the majority, if not all visible light out of my photos. In fact most of the photos featured on JerHetrick.com were captured using a 920nm filter which is well above the visible spectrum of light.
First thing is first! You need a modified camera to do infrared photography. You can use infrared filters on non-modified cameras though the exposure lengths required to capture usable images are usually going to be to long. This 30 second exposure was captured using a non-modified Canon DSLR with a 920nm infrared filter attached. The conditions were perfect for infrared photography. The sun was out and extremely intense.
I was experimenting to see how long of an exposure it would take to get a usable image with a set up like this. I finally attached an intervalometer to the Canon 7d and took a 10 minuet exposure. The 10 minuet exposure was still to dark to use. So having a full spectrum modified camera to do infrared photography is imperative, despite what some people online try feeding you.
If you are wondering why infrared photography with a stock camera does not work it is because camera manufactures use UV/IR cut filters to eliminate any chance of the camera introducing infrared light into the sensor of the camera producing undesired photographic effects. With this filter removed your camera becomes sensitive to the entire electromagnetic light spectrum. The following image will give you a better idea of what we are talking about.
Camera manufacturers like Canon use UV/IR cut filters which block light waves up to about 350nm to 400nm, these filters then allow wavelength transmission up to about about 600nm to 700nm where the filter then blocks all wavelengths above that transmission point.
All UV/IR cut filters fall short of eliminating all Ultraviolet and Infrared light, which is why you can do infrared without a conversion. A very small amount IR and UV will always be leaked to the sensor of the camera.
The following chart shows the transmission curve of some of the more popular UV/IR cut filters on the market today. So if you refer to the first scale and then look at the chart below you will have a better understanding of how these filters work. Keep in mind this is a universal chart used to display the characteristics of all wide band, narrow band and notch filters. Does not matter what the optical filters purpose is.
Hopefully you can clearly see why it is absolutely necessary to have the UV/IR cut filter removed from your camera. And why infrared photography with a IR/UV cut filter in place is an absurd idea!
With the stock UV/IR cut filter removed from a camera, the camera’s sensor will be left wide open to the entire electromagnetic scale of light, not just the visible scale. This is a photo captured with a camera that has been full spectrum modified. Meaning the UV/IR filters was removed and replaced with a piece of clear optical glass, commonly referred to as a clear glass filter.
As you can see the photo has a reddish tint to it and the green vegetation has a reddish hue as well. This is infrared radiation, the red spectrum on the scale above that is normally blocked out by the camera’s IR cut filter. Generally this is not a desired a effect, so we have to harness the power of this camera by using infrared wideband filters.
These filters come in a wide array of options. The most common though are the 650nm, 720nm, 760nm, 850nm, 920nm and 950nm wide band filters.
Most of the work that I do is with a 920nm filter, though I believe the most common filter out there is probably the 720nm filter. Although Ive noticed a trend toward an even wider filter which is the 590nm filter.
In absolute simple terms the lower the bandwidth, the more visible light the filter is going to allow to pass to your cameras sensor. These lower bandwidth filters are also known as near infrared filters.
The way that these filters work is commonly misunderstood. The infrared filters being marketed for photography are not notch filters, meaning that a 720nm filter is only going to allow the light in the 720nm range through. A 720nm filter will begin allowing light to pass at about the 720nm wavelength and allow all wavelengths about it to pass as well.
This is a representation of how a 720nm wideband infrared filter works.
So as you can see from the above diagram a 720nm filter will prevent most visible light from passing through the filter while allowing from 720nm and beyond through. I think the biggest misconception is that these filters act as notch filters allowing only 720nm wavelengths through. There are filters generally used by astrophotographers and other specialized imaging processes that do in fact do this. Though these filters are generally very expensive.
A good example of a notch filters are Hydrogen Alpha, Oxygen II and Sullpher III filters used to capture very specific wavelengths of light from astronomical objects. A Hydrogen Alpha filter allows 656.28nm wavelength through + or – normally 3nm to 12nm. So a + or – 6 Hydrogen Alpha filter will allow wavelengths through from 650.28nm to 662.28nm and then cut out all surrounding wavelengths.
Hopefully you have a better understanding of how filters work pertaining to infrared photography. If you have any questions, or need any help understanding further please feel free to contact me.
Till next time, peace out Jer!