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Peak spectrum sensitivity of typical BSI CMOS camera, red or infrared? Brightest wavelenght IR LED?


Avalon

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I was analysing quantum efficiencies of CMOS camera‘s in full spectrum mode and seems that peak is somewhere among 500-600nm although it does varry model to model. Obviously most popular camera sensors were designed for best performance in visible spectrum. I guess red peak can be explained as need to compensate for IR hot mirror filtering. Other thing I noticed when modifying various camera‘s is that IR filters do seem to be different in thickness and some have different degree bluish and even greenish tint. Filter I removed from Sony A3000 was more thicker and blue tinted than in Fujifilm Finepix F500 which had very thin filter so it seems there is more need to supress infrared on bigger pixel sensor?

Some infrared CMOS/CCD are more sensitive to longer infrared rays and can even sense some SWIR like Contour IR digical camera – their peak sensitivity is range of 800-850nm. When I asked manufacturers how they achieve it they explained me their CMOS sensor based on metal doped silicon and quoting following ”Metal produces additional carriers and helps to narrow silicon bandgap which results in absorption (to be specific two-photon absorption phenomenon) of lower energy photons (longer wavelengths). “ Also their sensor is monochrome which makes it further more sensitive.

I also saw post that pixel deeper wells increase sensitivity to infrared and it makes sense since silicon becomes transparent at longer wavelengths and these wells are deeper in bigger pixels camera’s – high sensitivity professional photography camera’s among which Sony A7S has largest 71.24µm2 size pixels. However I could not find scientific paper to back up this claim.

I was also curious what this peak could be on normal camera’s modified to full spectrum with sensor utilizing rarer RGBW color filter array for example in newly released Sony A7S III? CFA especially blue and green channels can block significant amount of NIR.

I tested my full spectrum Sony A3000 camera on infrared flood light I built from 3W three 850nm LED’s and nine rarer 830nm LED’s and they seem to have all same brightness. In visible 830nm are more reddish, with 930nm filter 850nm are brighter so they are not fake.

For nightvision devices’s typically are used 850nm LED illuminators which happen to be lowest cost. There is consideration that they need to be unspottable to humans or animals so longer wavelengths like 940nm can be used, also longer wavelengths require lower voltages. There are premium 810nm illuminators which claimed to have higher distance illumination than longer ones. But again they are designed for digital or analog GEN 3 nightvision which has enhanced IR sensitivity and special AR coatings for lens.

Most popular IR LED’s on Ebay are 740nm, 850nm and 940nm. However more rare and expensive versions exist like 808nm, 810nm, 830nm and so on are made too. I want to use mirrorless camera for watching/documenting wild life so I guess 740nm or shorter could spook them especially concentrated beam required for longer focal lengths. Unfortunately my setup doesn’t have sufficient long distance illumination for real time imaging/filming, max ISO is just 16000. Even for A7S with fastest f/0.95 lens passive night vision still is challenging. But maybe A7S III full spectrum modified with APS-C speed booster could work out better since a lot of light is wasted on rectangular sensor.

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My A7S does very well at night, even for video, with a fast lens. Moonlight is plenty at 30 frames/sec. The eye is less sensitive to noise in moving images so you can really crank up the ISO.
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The Sony A7s mk3 just has a regular rgb BSI type sensor. Not a RGBW type as rumored years ago. It does have a white balance sensor on front which is a little unusual.

 

The only commercially available RGBW sensor I know of is from Arducam:

https://www.arducam.com/product/16mp-imx298-color-mipi-camera-module-raspberry-pi/

 

But for high sensitive IR with global shutter you might be more interested in this monochrome sensor:

 

https://www.arducam.com/product/arducam-ov9281-1mp-global-shutter-noir-mono-mipi-camera-with-130deg-m12-mount-for-raspberry-pi/

 

The Raspberry pi systems can built nearly anything these days. Also not too expensive.

 

I have shared some of my code. But for video you would want raspivid.

 

The newer Arducam sensor boards are now gaining direct support.

 

More details on the 9281 chip:

https://www.arducam.com/docs/cameras-for-raspberry-pi/mipi-camera-modules/ov9281-1mp-global-shutter-raspberrypi-camera/

 

 

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A7S are best series mirrorless camera's in terms of low light sensitivity, better are maybe rare camera's like x27 or unaffordable medium frame ones. I don't know maybe there are similar full frame camera's with higher resolution and pixel binning technology but A7S III still uses 12Mp sensor for a reason. Some camera's can ramp up ISO even to higher levels but as noise sacrifice. Noise however can be reduced by Peltier cooling, I noticed even A3000 had strange big gap behind sensor.

 

The Sony A7s mk3 just has a regular rgb BSI type sensor. Not a RGBW type as rumored years ago. It does have a white balance sensor on front which is a little unusual.

 

The only commercially available RGBW sensor I know of is from Arducam:

https://www.arducam....e-raspberry-pi/

 

But for high sensitive IR with global shutter you might be more interested in this monochrome sensor:

 

https://www.arducam....r-raspberry-pi/

 

The Raspberry pi systems can built nearly anything these days. Also not too expensive.

 

I have shared some of my code. But for video you would want raspivid.

 

The newer Arducam sensor boards are now gaining direct support.

 

More details on the 9281 chip:

https://www.arducam....berrypi-camera/

 

Oh, really? What a shame, this could have been serious sensitivity improvement. Or RGBW do come with problems?

 

I recently saw some phone models to use such filters arrays but rather then stick to Huawei P20 PRO which has secondary monochrome camera's and even bigger sensors than Arducam. And what's the point in wasting time/nerves building them if ready package at not so high cost can be used. I can seem to find full frame sensors, that would actually worth looking into.

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Ok seems like you know what you want and it seem like you want a 135 format camera.

Go for it.

 

Not necessarily full frame, APS-C or even a bit smaller sensors (and cheaper) can still be good provided high sensitivity technology is used especially in this case in infrared spectrum range. I don't know how well Contour CMOS 400-1700nm with 3,75×3,75µm pixel camera compares to mirrorless camera's I mentioned. Tests must be done. Maybe someone knows not terribly expensive large sensor monochrome USB camera's or even digital night vision devices? I can't find ones with 35mm nor APS-C sensors but maybe that's because they adhering to different standarts. Or perhaps maybe I should wait for graphene based CMOS camera's with impressive sensitivity.

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The Contour is a two-photon sensor type device. They are highly nonlinear (see my experiments with one of these on the board) so require a ton of light intensity at SWIR wavelengths. Might not be bad at 850nm though.
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With my camera I notice a big difference in sensitivity between 850 and 940 nm. I just got a 1000-1050 nm LED, the "10 W" type, I didn't test it properly yet but I can tell my camera has a very low sensitivity there.
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