Black anodised aluminium in IR

The reflections we cannot see

lens hoods

Pedro J. Aphalo






NIR, reflectance, hotspots


I have added a section about the “blackest black” paint, which is still incomplete as I haven’t done any tests with this paint yet. I also merged updates from 2018 and 2019 into the main text.

Commercially available lens hoods

Many cheap extension tubes, lens adapters and lens hoods are made of aluminium and have a black anodised finish: are they always better than plastic ones? As it was revealed by the macro extension tubes comparison internal reflections can be a problem in visible light and lead to glare and low contrast. These problems are caused by a relatively small amount of visible light reflected by anodised aluminium, specially if the surface is smooth. The ribbed surface frequently used avoids specular reflections, so controlling “stars” and similar artefacts but not so much the loss of contrast due to diffuse reflection.

Figure 1: Two aluminium lens hoods which look almost identical under visible light. Both bought from eBay sellers. (The white slab on the left is a piece of PTFE used as white reference.

Black anodised aluminium looks black as it absorbs most visible light, although not all of it. At some angles of incidence some light is reflected and and the surface may appears shiny. In the near infrared region the problem is many times worse, as black anodised aluminium reflects a large fraction of the incident radiation. Lens hoods that look almost identical under normal illumination, may differ in being coated or not on the inside. The hood from RISE(UK) is not suitable for NIR imaging while the one from JJC is, and probably this second one is slightly better also for visible light photography.

Figure 2: The same two lens hoods from Figure 1 look quite different when under near infrared (930 nm LED) and photographed with a digital camera converted to “full-spectrum”.

Most expensive macro extension tubes, lens adapters and lens hoods, and occasionally also some cheap ones, are painted matt black on the inside, and this is one of the reasons why they perform better. Those who build telescopes as a hobby use, as an easy to find non reflective paint, black blackboard paint. An alternative is the use of black flock or black velour. Black flock with self stick backing is available but can collect dust.

As some of the cheap aluminium-made Chinese macro extension tubes and lens hoods are of good quality except for the NIR-reflective and partly VIS-reflective inner surfaces, and as equivalent items are not always available with a better finish, I have started some tests on how to improve the optical performance in the NIR waveband of a lens hood, hoping later to also improve extension tubes and lens adapters.

Black blackboard paint

My first trial was with water-based black acrylic blackboard paint “Déco additif” peinture ardoise/boad paint (Lefranc & Bourgeois, Le Mans, France). I painted a lens hood of a length not available from JJC. The result was a significant improvement, but not as good as I would have liked. I will try with a third coat, but apparently this paint is not fully matt.

Figure 3: The lens hoods differing only in their length, but both with the black anodised aluminium finnish. The one on the right, painted on the inside with two coats of black blackboard paint. An improvement, but far from perfect.

I end with a comparison with an original lens hood from Olympus, frequently described as grossly overpriced for a piece of plastic. Even if made of plastic and light in weight, its performance is excellent both in the visible and in the near infrared regions of the spectrum.

Figure 4: The same lens hood on the left and an original lens hood from Olympus on the right side. They look quite different when under near infrared (930 nm LED) and photographed with a digital camera converted to “full-spectrum”

In conclusion, when possible, it is probably best to stick to original-equipment lens hoods supplied by the manufacturers of high quality objectives (caveat: I have tested only Olympus hoods). I used the painting of the lens hood as a test, as I need screw-on lens hoods with a 52 mm thread for use together with special filters of this size, as I use them with step down rings, which prevents the use of the original lens hoods.

Tetenal camera paint

For the tests with adapters and macro extension tubes, I bought a special camera paint by Tetenal, giving less than 5% reflectance. (I have to thank Hannu from Teknofokus for the tip about this paint!).

Photograph of work table

Lens hoods, macro extension tubes and some mount adaptors after being sprayed with the special black paint from Tetenal. I removed the mount rings from the adapters before spraying them to ensure that they remained free of paint, and I protected some other parts with masking tape. Once the paint has dried I reassembled the lens mounts of the adapters.

Tetenal’s camera paint works both in the visible and NIR. For the photograph bellow IR illumination was more diffuse than earlier. That Tetenal camera paint works better than the acrylic blackboard paint is clear when comparing Figure 3 and Figure 5. Even though there is more reflection than from the Sigma plastic lens hood, straying resulted in much better and more even coverage of the aluminium surface than brush painting with blackboard paint.

Figure 5: The same lens hood on the left after being painted on the inside with Tetenal camera paint and an original lens hood from Sigma on the right side. They look quite different when under near infrared (930 nm LED) and photographed with a digital camera converted to “full-spectrum”.

The Tetenal paint comes in a spray can and is based on organic solvents. It has a high load of pigment as almost all really mat paints. It is flammable and toxic and should be used in a well ventilated place.

The blackest black paint

[Section added in 2023] I have bought a bottle of “BLACK 3.0” paint (“BLACK 3.0 paint is even blacker than BLACK 2.0 and the Tetenal paint). Being an acrylic paint, it is water-based and non-toxic. The developer of this paint, Stuart Semple, and his team are very helpful and friendly and have even supplied spectral data to me.


If you use lens hoods only for visible light, you should be able to approximately gauge their reflectance by eye. If you take images beyond the visible, tests are needed, specially for NIR. I have tested these same lens hoods in ultraviolet A (365 nm LED), and they all absorb UV-A radiation quite effectively.