5 tips to using an infrared filter on front of your lens

Recently, I wanted to try infrared photography. The infrared part of the electromagnetic spectrum is invisible to the human eye, so we normally can’t see it. However, a camera sensor can be set up to detect it. The proper (and expensive) way to do it is to send your camera off to a specialist (I’ve heard good things about Advanced Camera Services, if you’re interested), who will remove the infrared blocking filter in front of your sensor, and replace it with a filter that only allows infrared light in. Sometimes infrared cameras appear on eBay as well.

The cheap way to try it is to use a filter that goes in front of the lens that cuts out a lots of the visible light and lets in just red light. I purchased this set of filters from Amazon with a 55mm filter thread that would fit most of the lenses I use with my Sony D-SLRs.

The filters that came had ratings on, depending on how much visible light they cut out: 720, 760, 850 and 920nm. When I tried them with my a55 and a77, only the 720nm would let in any light, so I think the low pass filters are blocking out the rest.

The first thing you notice with the filter on the lens is that a lot of light is locked out. Using the sunny 16 rule, I calculated that about 10 and a third stops of light are cut out.

I used the the filter on my a55 and 18-70mm lens on a photo walk around the South Bank and got some good looking shots. I didn’t have a tripod with me, but I was able to blur the water in this shot by perching the camera on a wall. I really loved the look I got:

St. Pauls

So far, so good. However, when I looked at the image carefully, I could see that the image wasn’t quite tack sharp. My focus was slightly off. This is due to the fact that infrared light needs to be focused differently to other light. Some lenses show you exactly where the focus should be. For example, in the days of film, you could load infrared film into your camera and shoot that way. Here is a picture of my dad’s Vivitar 135mm f/2.8.

IR Focus

The red line between the 8 and the 16 lines show where the focus should be if using infrared film.

However, none of my lenses have this feature so I decided to get around the problem by shooting very wide angle.

There’s a rule in photography that says: if you reduce your focal length and keep everything else the same, more will be in focus. What that means is that when you shoot very wide angle, it’s easy to keep everything in focus. If you shoot telephoto, the opposite is true, get your focus off by just a bit and it will be immediately noticeable.

I own a very wide angle lens, unfortunately, the filter thread is different, so I ended up having to purchase another infrared filter, this time with a 82mm filter thread. I went with the ZoMei 82mm 720mm Infrared filter.

With this attached, and following what I’d already learnt, I got some great shots on my recent trip to the south of Spain. I ended up combining all the previous with a HDR blend to get an image of a farmhouse in Fines.

To the ground

So, to summarise, my 5 tips for shooting with an infrared filter in front of your lens are as follows.

1. Shoot wide. Most kit lenses will shoot at 18mm: start there.

2. To get everything in sharp focus, shoot with a narrow aperture. I was typically using f/16.

3. Set your shooting mode to black and white. The infrared filter will only let in an ugly red and orange light, so review your images in black and white.

4. Use a tripod. If you want to shoot at ISO-100 at f/16 with an infrared filter on, your shutter speeds are going to be greater than five seconds on a sunny day. The alternative is to bump your ISO up, I could get away with ISO-1600 or 3200, and my shutter speeds were usually around one tenth of a second.

5. Shoot in manual, and use live view. It may be difficult at first to figure out your exposure exactly, so shoot using live view to allow you to see the image before you shoot. With time, you may be able to use aperture priority with some exposure compensation dialled in.

Thanks for reading to the end. If you enjoyed reading it, why not leave a message, share on social media, or have a look at some of the other articles on the site?

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