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Questions about ThermApp

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Hagrid:
Hello everyone, some of you maybe know the ThermApp thermal camera made by Opgal. This camera has a focus able lens which is really nice in my opinion. However, it also enables the user to change the lens. So while the lens is removed dust and other nasty stuff can get stuck on the sensor and accumulate over time.
This makes me think if such a sensor can be cleaned somehow at all. Most LWIR optics are coated as far as i know, so i assume you could ruin your sensor really fast.

Greetings, Hagrid

Ultrapurple:
Looking inside the Therm-App you'll see the exposed front surface of the Ulis microbolometer sensor (see photo - the spot middle bottom is a reflection not contamination). So yes, unless you practice reasonable hygiene you could end up with muck on it. However, I've been changing Therm-App lenses frequently for years in conditions ranging from home to the edge of the Sahara Desert (yes, really) and I've not yet caused any problems. As long as you use a similar level of caution as you would changing lenses on a DSLR, you'll be fine. My tips are


* Ideally, only change lenses in a clean area free from airborne contaminants, grit, grease, small children etc

* keep the body of the imager facing down when you remove the lens, and place it opening-down onto a clean surface

* put the removed lens into a clean container straight away

* get the next lens from its clean container

* if you're feeling enthusiastic, use a bulb-type blower to make sure there's no contamination on the sensor-facing part of the lens assembly

* screw the lens into the housing and adjust focus to taste

If you do get dust or hair contamination on the sensor, blow it away using a bulb-type puffer or a photographic-quality compressed air stream. Do NOT use your breath. There is no reason why a properly-handled Therm-App should ever get, say, fingerprints on the sensor.

Most of the time I keep my 13mm f/1.0 lens attached and only change to the other lenses when there is a particular need.

Ultrapurple:
In case anyone's interested, I took a look at the Therm-App Pico384 sensor using another Therm-App. Almost none of the detail is visible to the naked eye because it's all sealed behind a slice of germanium.

The image below is a stack of about 250, processed in Registax 6 and Paint Shop Pro. I know it's a bit fuzzy but bear in mind the source was 384 x 288! I captured the image using a 13mm f/1.0 lens screwed out to its maximum extent (max macro). The 'vignetting' at the corners is caused by the round lens aperture of the camera body (see visible image posted previously, which is rotated 90° from this thermal image).

While I was working on this I discovered that fingers clutching the lens for focusing make a pretty good ersatz thermal ring flash!

A better but smaller version of this image is at https://www.flickr.com/photos/ultrapurple/35902887753/in/pool-therm-app-users

Hagrid:
Hello again, thank you for the advice to keep the device clean. I noticed that your Therm-App on the picture has no grease on the thread. Mine came with quite some. The inner part of the camera isn't painted too. So i suspect they have changed manufacturing them over time.
The picture of the sensor is really interesting, thank you a lot for this! It is good to know that this sensor is sealed behind germanium. I suspect it has a similar coating than the lenses usually have? However, it doesn't look as shiny as the surface of the lens.

Greetings, Hagrid

Ultrapurple:
The early versions of the Therm-App had no grease on the threads and as a result the lenses wobbled slightly. Not enough to worry about falling out, but definitely sufficient to throw the focus off. The lens wouldn't be quite parallel to the sensor.

I haven't heard of the inside being unpainted. I'd always assumed it was anodised, for strength and corrosion resistance, like the outside. Perhaps you could post a picture next time you're changing the lens?

I don't know whether there is a coating on the window. I suspect so, but it's hard to tell with human eyes! The data sheet may reveal more: if anyone has a copy, could you check please?

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