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UltravioletPhotography

Modifying and enhancing phone camera‘s for UV/VIS/IR photography?


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Hello. I do have APC-C full spectrum modified mirrorless camera I use for photography but I not like it for several reasons. DSLR/mirrorless camera‘s are bulky and heavy, require more expensive and larger lens and filters, are limited to factory software which gets eventually outdated.

Sure bigger sensor/pixels and fast aperture lens camera‘s will still rival over phones especially in low light conditions as well for having viewfinders, screw in filters and hoods but I can‘t just carry bulky camera everywhere I go, when for example exercising, hiking and traveling. Somewhere I saw good quote: best camera is which you have available when it‘s needed. And there are rare, unpredictable moments to take that amazing shot.

I researched many currently released phone camera‘s to find out which of them have biggest sensor/individual pixel sizes, fastest lens, fitting color filter arrays or monochrome sensors, wide range of ISO settings, as well quite recent technology such as pixel binning, multiple camera combination for higher dynamic range and sentivity or great optical zoom, PDAF/laser focus. Also display quality and overall hardare quality, operating system was important factor. If someone would be interested I could send you list of phone camera specs I made in 2019, currently there are of course new improoved phones camera‘s released.

Of all of them Huawei P20 PRO to my mind is most interesting due to these reasons:

1) It has tripple camera system: main one 40 MP, f/1.8, 27mm (wide), sensor size 1/1.78" and pixel size 1.55μm, second 8MP 80mm telephoto f/2.4, sensor 1/4" and third one 20MP monochrome f/1.6, 27 mm, sensor size 1/2.7", pixel size: 1 μm.

2) Monochrome sensor is much more sensitive to visible light and significantly to shorter UV rays, IR sensitivity is also a bit better since green/blue filters block some of the NIR spectrum.

3) Pixel binning. When using pixel binning resolution is reduced by four. Although I have seen reports that low resolution sensors are still more sensitive than high resolution binned sensors due to photodetector deeper wells which able to capture more energy (as well there were reports deeper wells allow to detect longer IR wavelengths, can A7S do it?). There are camera’s that can combine even more pixels like for example Samsung Galaxy 20 Ultra which can use even 9 pixels but since it has ridiculously high 108MP resolution pixels are only 0.8 μm big.

4) Lens are pretty fast however later Huawei P30 PRO phone main camera has even faster f/1.6 lens. Honor 20 PRO has fastest known phone lens with record aperture of f/1.4 what it makes interesting to use it for modification of Huawei camera. Lens are made by German Leica company which probably produces sharpest and highest quality lens in the world. Although they are made not from glass but plastic which spectral transmission is unknown to me. AR coatings and optical cement might also block UV but to know for sure tests must be done.

5) ISO ranges from 50 to whooping 102400 what is useful for low light imaging when there is no time for long exposures. I want to turn this phone into night vision device to work with my powerful 830-850nm LED lamp so high ISO noise is not so much an issue. There are Apps which can overdrive sensitivity even to higher levels. I’m curious if it would be possible cool phone camera sensor for better signal to noise ratio?

6) Android is most popular OS and has highest diversity of Apps available. Also wide selection external USB devices and cameras can be connected to phone via micro USB port. I saw there was even full frame camera that could be connected to phone but it’s expensive, maybe someone can recommend big sensor low cost USB camera? I noticed also phone LWIR thermal camera’s with great specs are less costly.

7) High resolution, contrast and brightness OLED 90hz display. Phone display can be turned into viewfinder with VR glasses or monocular adapter.

8) Huawei P20 Pro is premium phone but over time it’s price had dropped significantly. Also camera modules are easy to access without risking breaking OLED display and are cheap to replace in case of failed modification.

Sure there also other good phone camera‘s. Sony Xperia XZ2 Premium has biggest and fastest lens monochrome camera, as well highest video ISO. Panasonic Lumix Smart Camera CM1 and Nokia 808 pure view have biggest sensors among the phones but they use not backlit BSI CMOS or are outdated. HTC phones known for biggest pixels but have low resolution. Nokia 9 PureView went in different path by using unique 5 camera design where three of them are monochrome. And lastly Samsung Galaxy S20 Ultra and Huawei P40 Pro have biggest sensors of all modern phones, too bad they lack B/W camera. Huawei P40 Pro has 1/1.28" size sensor and 2.44µm pixel size what makes it most sensitive phone camera to date. In theory it’s possible to remove CFA from sensor but from my experience its very risky operation and microlens would be lost (if they are still used), I could not remove Bayer filter from some sensors at all although I might try using stronger solvents. Any idea if it would be possible to do such modifications with Huawei P40 Pro?

Modifications I want to do are to change hot mirror in monochrome camera to UV pass/IR cut filter since it‘s best suited for UV photography. Main p20 PRO camera would be used for VIS/IR photography with sliding IR-cut filter. I also want to change lens in main camera and maybe monochrome also to Leica f/1.4 what would significantly increase light gathering. I‘m not sure what field this lens actually covers and if it would produce vignetting on 1/1.78" (14.27mm) sensor, it‘s designed for 1/2" or 12.7mm sensor but I think there might be little room left to avoid edge blur/vignette. I had idea to add external mount for M12 lens which apertures can go as wide as f/0.95 but I prefer to use quality Leica lens which hopefully could fit inside phone and provide autofocus. Most phones today use plastic lens however LG V30 phone is exception that uses f/1.6 glass lens which might have better UV transmission but I have no any idea of their transmission capabilities.

Some incredible engineering went into squizing as large as possible sensors and wide aperture as well great zoom lens to maximize versatility of camera‘s in such thin phone design. In near future novel technology might be used such as graphene based CMOS sensors reported to be 10 times more sensitive than current silicon sensors with super broad spectral response from visible, infrared and reaching even terahertz range. Lens could be made as thin as 600 nm and flat with entirelly different metalens which focus whole spectrum into one spot thus having no chromatic abberation and requiring less lens elements. Such technology could even make traditional photocamera‘s obsolete at least for most users.

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I would second Colins idea of setting up a pi camera system.

I just recently got a Pi4 board, a HQ camera, a ups hat (takes 2 18650 batteries for power) and a 4.3 inch touch screen. All very cheap from waveshare.

The pi hq camera will allow for easy modification.

You can write python script in raspberian or use a gui one available for modification.

Or you can load ubuntu on the pi.

Or you can load android on the pi.

There are many options.

 

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Andy Perrin

Around 2012, I converted an iPhone 4 (old even at that time!) to IR. I found that the window on the case on that phone was blocking most of the IR, and the lens passed it fine. It did NOT work for UV at all, however. It was both insensitive to UV and also there was massive focal shift.

 

Here is a sample of what I got in UV, using a 12mm 330WB70 filter:

post-94-0-81757300-1593964865.jpg

 

It worked better with Hoya R72 (which I ground down by hand with a dremel tool from a 52" filter!):

(This is a "long exposure" made with a special app.)

post-94-0-97313600-1593965066.jpg

 

Single frame (to give an idea of the quality at that time):

post-94-0-28460000-1593965128.jpg

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I converted the back camera of a Samsung GT-I0970. It worked well for both UV and IR. It didn't have autofocus, but I could screw and unscrew the lens, focusing from infinity to basically macro.

 

ZWB2 (2 mm) + chinese BG39 (2 mm)

post-284-0-18945600-1593970120.jpg

 

It is dark, I know, but I really like it.

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...but then I tried to remove the CFA...

Ruined sensor (in the second image, which is UV BTW, you can see some dead lines), but sensitivity improved a lot (look how darker are the magenta regions...

 

post-284-0-30149300-1593969893.jpg

 

post-284-0-23285000-1593970159.jpg

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Andy Perrin
Very interesting, Stefano, especially the debayering. (You should probably shrink those images before uploading...)
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Very interesting, Stefano, especially the debayering. (You should probably shrink those images before uploading...)

I uploaded from my phone. I don't usually do it, but this time I was too lazy. I usually post images 1000 pixels wide.
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Andy Perrin
I'm seeing some evidence of the focal shift issue in your images too, although not as bad as my old one.
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Don't have much experience with raspberry pi camera, only once I did saw papper describing DIY ultraviolet PiCam camera which was BTW also using smartphone monochrome converted camera and used quartz lens: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5087437/#sec2-sensors-16-01649titl

Unfortunatelly I do not have advanced understanding in electronics and programming, probably waste a lot of time and money than just using ready made camera's with simpler modification unless I could hook up full frame/APS-C camera to phone.

 

Interesting photos Stefano, light gain is evident. I also ruined a lot sensors trying to debayer them, maybe frontlit CMOS/CDD camera's are more fragile than backlit ones probably due to exposed electrodes, some of them have very weak golden wires which I did break often. I used ethanol, acetone with micro cotton swab, sometimes plastic or softer metal to rub of sensors, in some cased I could remove CFA in other I could not like my old Samsung phone. Some sensor have impossible to remove glass cover. Problem with using acetone is that it quickly evaporates. Now I have access to dimethylformamide, monoethylene glycol and other painting restoration solvents which are pretty strong solvents so I could try using such. In astronomy forum I saw another method involving sandblasting sensor with somekind particles.

 

Are here anybody who monochrome converted modern BSI CMOS camera's?

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