Many IR filters made of glass are expensive, especially if you buy them for lenses with a wide front diameter. In the last few weeks I have started to use more and more very inexpensive filters made of polyester film.
Not only do they cost a fraction of glass filters, but they allow a range of fine tuning and experimentation. And as far as quality goes, I don’t notice any difference. On the contrary, they are often more translucent (i.e. you can shoot with faster shutter speeds) and hotspots and reflections caused by the glass do not occur either.
So how do you build a cheap IR filter? And how do you attach it? I have been testing for a few weeks now and my girlfriend had this great idea.
The crucial question is: Can I attach the filter behind the lens? Not every lens is suitable for this. You need one where, first, the lens doesn’t protrude too far, and second, that lens is enclosed by a wide enough ring so that the filter holder has enough surface area for attachment. In addition, the filter construct must be very thin so that the mirror does not bump into it when it is released.
If you have such a lens, for Nikon it is for example the standard zoom 18-55mm, then you have to calculate the diameter. So look how wide is the area that moves down and up when zooming in and out. First, we are interested in the total diameter of this “platform”, second, the diameter of the glass inside the ring. Once you have the dimensions, you can look for a suitable paper punch that can punch out these sizes.
The following picture shows the material I use:
– Swatchbook by Lee Filters
– Double-sided, thin adhesive tape
– Regular tape
– Paper punches in 2 different sizes, for example these
– Scissors and sturdy paper
Now find a sturdy paper, fold it. Punch at the fold, first with the small one, and exactly over it with the larger one, creating a ring that is closed on one side. Looks a little like a seat ring for the toilet. Now cut one layer of the paper (see main picture above) so that you can insert the filter.
Tape the filter holder on the left and right side so that the filter can’t slip out. Attach the holder to the ring with double-sided tape.
Now cut out the filter so that it fits and can also be pushed out with your finger – I found an angular, irregular shape better than round here. That’s it. This is how you create a cheap IR filter and a filter holder.