Doing Interval Photography on a Sigma SD14 – 2

Figure 1:  DIY adapter for the camera

So, with the camera adapter up to snuff, and able to run days-on-end, I still needed a few pieces/parts to flesh out the IR inventory.

As was noted on another of my pages, a visible light blackout filter is needed for high-mid range IR photography.  This is because the sensor is less sensitive as the ambient IR light gets closer to (about) 1.5 microns (I believe it’s in that area, anyhow) , and so a longer time exposure is needed to allow the buildup of the signal into a reasonable photograph.   Visible light would quickly over-expose the whole frame, since the sensor is more sensitive to visible light than to IR light.

The sensor in the SD14 isn’t officially rated to go all the way to 1.5 microns.  If you look at some of the charts, you’ll see that the tail is pretty thin out there.  The only meaning in that is that more time is needed ( at least from my perspective).  If the sensor could collect a single 1.5 micron photon, then even tho it might take days, I’d still probably get a photography eventually.  This is all an empirical data pile that I’m growing as I go.  Stay tuned.

Unfortunately, the term “IR filter” is used for both IR blockers and for IR allowers.   What we need is a filter that blocks out visible light and “allows” IR light.  One needs to read the fine print in the advertisements to make sure the filter is the right one, because many IR blocker filters (not what we want) are sold to photographers because the IR is said to damage visible light photography.  BTW: “allower” is not a word, is it?  Should it be?

With the IR allowed, and the visible light shut out, we can then proceed to the next  problem, which is the need to capture “pulses” of IR light.  A time-lapsed photography technique can amplify pulsed IR light into a usable photograph.

To capture pulsed IR light, we simply need to lengthen the exposure window to include multiple pulses.  Eventually, the total number of photons in the pulses adds up to a level that can make for a photograph of the pulse.  However; leaving the time-lapse window open longer creates more noise, which would eventually overexpose the frame with noise.  Solution?  Neutral density filters.

I purchased a neutral density filter on Ebay for about ten bucks.  It’s variable.  Being variable is really neat, because I can shut down the exposure per  unit time to almost any value I want.  There’s a caveat here, which is that some neutral density filters only grade-out visible light, and allow all IR.  So, for the ND filter we need one that grades IR as well as visible light.

Figure 2: IR photo using (at least some) of the techniques in this post

The Foveon sensor uses the technique of silicon depth penetration to extract photon hits into usable sensor data.  This is way different than any other sensor.   What can happen is that unconventional angles of penetration can provide light registry of lower frequency (higher wavelength) photons.  There is a chance of receiving a photon that has a depth penetration that’s higher than what the designers designed.   This wouldn’t happen with Bayer style sensors, so those are pretty much clamped off in my opinion (I’m quick to qualify it as a non-expert opinion).  Again – in my opinion – this makes the Foveon sensor superior to others for my styles of IR photography.  I could be wrong.  The data’s still out there.

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The Sigma SD14 is a product of Sigma Corporation.  Sigma and Foveon are their trademarks.  This author and site has no affiliation with Sigma.  The Pentax K5 is a product of Ricoh Imaging Corporation, and is not affiliated with this author or site.

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