The ultimate Aerochrome filter?

Aerochrome – once again. For the umpteenth time I dedicate a post to this topic. Right at the beginning, I have to completely revise a statement from an earlier post: The DB940 is suitable for Aerochrome emulations. Even very well. Much better than the DB850. And maybe also better than the Triple Bandpass filter. Considering that it is also the perfect filter for blue vegetation (with blue sky, SOOC), it would probably be the best false color IR filter, the go-to model so to speak.

Let’s take a look at a photo. I used my Nikon D600 and the standard 50mm lens. The DB940 filter is attached to the back of the lens.

aerochrome filter

This is straight out of the camera and then white balanced on neutral sunlit asphalt. You can see the basic color of the vegetation, which is quite perfect: a strong blue in various shades. In contrast to the TB550/660/850 (Triple Bandpass Green+Red+850nm NIR), which SOOC gives a magenta coloration on trees et cetera and accordingly requires a strong adjustment in the Color Mixer.

This is the photo after the channel mixer – not bad either.

aerochrome filter

Let’s look at the crux of the matter: The color of the sky. This has always bothered me with TB, almost driven me crazy. Even today I don’t know why the sky always takes on a more magenta than blue hue. But it should be (as is the case with Aerochrome original) cyan-blue or – with stronger yellow or orange filters a strong dark blue.

The problem is that today there is a haze layer over the landscape and the sky has a rather weak and blue-violet coloration anyway – probably because of the heat at the moment. In any case, not optimal test conditions. This must be solved in further tests.

But let’s look at the current filter combination, which serves as a starting point.

My thought is this: The perfect (digital) Aerochrome filter would probably be a triple bandpass filter that doesn’t pass 850nm, but 940nm. That doesn’t exist. But you can get close to it by combining the DB940, which passes the complete visible spectrum as well as infrared from 940nm, with other filters.

You need a combination that creates two “transmission peaks” in the range 550nm (green) and in the range 660 (red). How can this be done? With an orange/yellow filter and a blue filter. In this case my Tiffen 16 Orange-Yellow and a filter from Lee called Slate Blue.

So we’ve created something close to a TB940. Maybe that would be a next project for Midwest Optics – the ultimate digital Aerochrome filter. More tests incoming…

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