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IXUS 230 HS infrared conversion

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IXUS 230 HS infrared conversion
« on: 09 / October / 2015, 08:57:45 »
Hello everyone,
As this is my first post, I'd like to start by saying thank you to the CHDK developers for their excellent work. I hope I'll be able to contribute.

Some 2 years ago I started playing with infrared photography using a mono CCD (which I normally employ for astroimaging) and an IR-pass filter. I liked the results, so last year I decided to try and remove IR-cut filter from my old Sony DSC-H10. It worked, but not very conveniently. There is of course no RAW support and not even a custom WB setting. As you can imagine, any post-processing of JPEGs quickly brings out denoising and compression artifacts, so in practice the images had to be downsized from 8 to 2 MP to look acceptably.

I had a plan to make another conversion, this time of a mirrorless camera, but then started reading about problems with wide-angle focusing requiring replacement of the sensor glass (Micro 4/3: 4 mm thick!) - doable, but expensive. I prefer to use my existing IR-pass filters.

Luckily I remembered the CHDK and started hunting for an adequate Canon compact; finally I chose the IXUS 230 HS. RAW support works great, though saving was slow on my old SD card (CHDK benchmark showed ~8 MB/s and RAWs are ~18 MB). After replacing it with a new 32 GB SDHC ("40 MB/s" sticker, ~20 MB/s in benchmark) the saving time is much better.

After disassembling the camera it turned out the sensor assembly screws are secured with glue drops (see sensor1.jpg). I used a small scissors blade heated repeatedly over flame to carefully scrape some of the glue away. Finally I turned the screws which cracked the remains.

The IR-cut filter wasn't attached in any way, it just rested over the lens. I verified its function by taking a photo with a mono CCD without filters and with an IR-pass (>742 nm) filter held in front (test12.jpg).

Re: IXUS 230 HS infrared conversion
« Reply #1 on: 09 / October / 2015, 09:00:37 »
There is an additional glass/optical window on the sensor, but it doesn't block IR (test 34.jpg).

I placed the IR-pass filter (Baader 685 nm, unmounted) directly on the lens. For now it's attached with adhesive tape scraps, but I'm working on a better way to allow quickly changing to a Baader UV/IR-cut (same size) for normal photos.
« Last Edit: 09 / October / 2015, 09:02:12 by GreatAttractor »

Re: IXUS 230 HS infrared conversion
« Reply #2 on: 09 / October / 2015, 09:07:24 »
Unfortunately the camera wouldn't focus at infinity in about lower 1/3rd of the zoom range. The IR-cut was thin but apparently moves the focal plane back quite a bit. I remedied it by getting rid of thin washers below the sensor assembly screws.

aptest12.jpg: test shots with the reassembled Ixus, showing its own IR-cut filter and Baader UV/IR-cut. Left: no filter, right: Baader IR-pass 685 nm.

Re: IXUS 230 HS infrared conversion
« Reply #3 on: 09 / October / 2015, 09:13:55 »
Finally, sample pictures attached. Now the plan is to shoot a cloudy IR timelapse (I already tried the "TimeLapseOne" script, works perfectly).

Re: IXUS 230 HS infrared conversion
« Reply #4 on: 09 / October / 2015, 21:51:55 »
Great build tutorial.   Thanks for posting all of that.
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