Huh, this looks almost perfect. Can you upload a picture of it with a light in the frame? I don't see any rainbow effects. Can you also send a pic of your DVD slice and its orientation over the camera? I worry it's not angled correctly and you're not generating a spectrum. You ought to see a bunch of rainbows here from these various lights!

Sorry it took a while to read through all the responses here but i'm glad you're getting help from @pushpaw too!

I also found this which, I'm reading at the moment:

https://publiclab.org/wiki/spectral-workbench-usage

Most webcams have auto exposure and color "correction" so that in dim light, you can still see. This will unfortunately change the exposure between readings, so for quantitative work, it must be disabled. On Linux, you can use the "uvcdynctl" utility as outlined here.

On a Mac, you can download this utility: http://www.phoboslab.org/log/2009/07/uvc-camera-control-for-mac-os-x

I'm playing with this right now:

https://www.npmjs.com/package/uvc-control2

Might do the trick, I'll post the update

OK, I'll resume tomorrow, but feels like I'm on the right track. Thanks a lot for the help so far!

Hi, what operating system do you use? There's some guidance on webcam selection here:

https://publiclab.org/wiki/spectral-workbench-usage#Webcam+selection

Thanks, Warren it MacOs and I'm looking at changing camera setting. I hope something like this might help:

https://github.com/HBehrens/CamHolderApp

In fact, if you have your photo film slit mounted on the slide in piece of card. Just slide the slit out of the way altogether. This was you are pretty much guaranteed to get some sort of spectrum. Then progress to small and smaller slits.

Pupshaw, thanks I tried that, it made no difference. I'll try to get the camera setting changed. Didn't have much time in the last few days, but this is what I'm looking at:

https://github.com/HBehrens/CamHolderApp

Unbelievable!, Linux has several free webcam utils and most web cams come with utils for Windows. I was struggling to come to terms with the idea that Mac OS has nothing bundled and that web cam manufacturers don't ship anything for Mac OS with their cameras, but it appears it's true. I guess this is part of the Apple 'It just works (except when it doesn't)' philosophy. A lot of the web cam utils that are available for Mac OS seem to be geared towards video conferencing and drawing silly facial features on selfies, which you don't really want. CamHolderApp seems of that ilk, it's designed for displaying what's happening on a smartphone screen and has things like Auto Focus that you probably don't want. What's needed for the spectrometer is a more nuts and bolts util that lets you set gain, exposure, white balance, colour temperature and so on. Then you need to work out which settings are best to set up the camera for best results in Spectral Workbench. Fortunately the Linux utility I use works with both my home brewed Logitech based spectrometer and with the camera in the PL Spec. 3. The tricky thing is that different cameras support a different range of controls and you need software that supports the camera you are using. GUCView supports both Logitech camera, which has more tweakable controls than the camera in the Spectrometer 3, and the Spec 3 camera. I did know what that camera was but I have forgotten.

CamHolderApp didn't detect the camera. So these are my next steps: 1. Connect the camera to Raspberry Pi Zero and access via VNC Connect: https://www.realvnc.com/en/connect/docs/raspberry-pi.html 2. Explore the idea of using Raspberry Pi Zero with its camera inside the original public lab enclosure (potentially with some 3D printed part).

Oh wow!! I want to know more about this especially:

spectralworkbench.org capturing images on Raspberry Pi Zero W with Chromium browser.

Umm... It's quite a while since I fired up my Raspberry Pi but as far as I recall it has a couple of activity LEDs plus two status LEDs on the network connector. You really don't want a load of LED's flashing inside the spectrometer housing. I think you will have to mount it to one outer side of the spectrometer.

Hmm! Interesting point. I didn't think about the flashing LEDs! But thinking about this, it should be possible to put some black tape on the LED. I'll try it. Talking about Chromium+VNC there's nothing special about it. It's just starting VNC server and then instaling an launching Chromium browser. The main issue is speed. It takes type to start the browser and it's not comfortable to work with. I'll try if I can access via Raspberry Pi via HomeKit/Wifi from my Macbook. It should be possible.

My experience is that blocking all the light from a LED indicator is a lot harder than you might think. Other than disconnecting the LED's almost nothing will guarantee no light escapes. You could try smearing a blob of plasticine or blutack over them, but you still tend to get diffused leakage (from the PCB mounted LEDs) through the PCB itself.

OK! Maybe it's possible to just disable LED via software:

https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi

I can confirm that this tuned activity LED on Pi Zero off:

#echo none | sudo tee /sys/class/leds/led0/trigger none

echo 1 | sudo tee /sys/class/leds/led0/brightness

1

I can't edit the previous comment, I get an error when I try. This is what I wanted to post:

echo none | sudo tee /sys/class/leds/led0/trigger none

echo 1 | sudo tee /sys/class/leds/led0/brightness 1

On Ubuntu 18 via VirtualBox camera is visible to the OS and on spectralworkbench.org you get a request for permission to use the camera. However the state of the camera remains "Requesting camera access... ".

I then tried "guvcview" and I get this error: V4L2_CORE: (get_v4l2_frame) video stream must be started first

I spent some time trying to resolve this issue, but I couldn't. I'll try older version of Ubuntu sometime later.

uvcdynctrl -d video0 -c Listing available controls for device video0: Brightness Contrast Saturation Hue White Balance Temperature, Auto Gamma Power Line Frequency White Balance Temperature Sharpness Backlight Compensation

This is great to see. Good work!

Thanks! Warren maybe you can post the settings that you use so that I can try them tomorrow?

I actually usually use default webcam settings! So going back to the original question, I believe there may be an issue with the angle or the orientation of the DVD... sorry, it's getting quite difficult to follow all the threads on this page --

In this comment: https://publiclab.org/questions/Tomas0413/06-16-2018/dark-images-can-t-get-spectrometer-to-work#a1034

You had a perfect image, so I don't believe there is a problem with the camera itself.

But I don't see any spectra even in that image, where we should. Can you upload a new picture similar to this one but clearly showing the DVD orientation?

Thanks for the response, I’ll upload tve image tomorrow. But aa far as I remember even if I leave only the camera inside the box the moment lid closed - it’s complete darkness. I saw somewhere on PublicLab that cameras were out of stock and then new ones arrived. Could it be that the model is slightly different? Could it be that the camera you use has AutoFocus off by default and the one I have AutoFocus on without an option to turn it off?

For example threre’s a similar camera on AliExpress and the description says that it’s AutoFocus and that this can’t be changed : Look what I found on AliExpress http://s.aliexpress.com/yEJbInIn

Great, i look forward to seeing the photos. Please also upload one of the front slit of your box!

I don't think autofocus would cause complete darkness! I'm eager to see how the grating is aligned and hope we'll solve this that way. Fingers X!

And this example says FixedFocus:

Look what I found on AliExpress http://s.aliexpress.com/yiIBvmiy

Your Guvcview control panel looks much like mine running on a real Ubuntu PC (If I understand you correctly you are running it in a virtual machine). Camera settings persist after I close Guvcview. Not sure why you mention auto-focus, you don't want it and I'm pretty sure the camera that ships with the spectrometer doesn't have it. Spectral workbench and /or the browser can be very picky about accessing the camera. When you run Guvcview do you see a spectral image in the viewing window? If not something is wrong with your slit or your diffraction grating.

Pushpaw, thanks for the reply.

Not sure why you mention auto-focus, you don't want it, and I'm pretty sure the camera that ships with the spectrometer doesn't have it.

I mentioned Auto-Focus, just guessing what if the camera model I received is not correct and what with I received a model with Auto-Focus. I took a picture of the camera and it says "NB23 S2", and the model I found on AliExpress (https://bit.ly/2m2ezVf) says it's fixed focus. So maybe this isn't a problem. I also removed the grating completely. So when the lid is lifted, I can get a good picture. When I close the lid, the image turns completely dark.

Warren, for now, I just completely removed the grating. And actually, I no longer use a slice of DVD, I bought a set of gratings (an upgrade). When I had grating installed, I noticed that part of the image is covered, so I need to check why. But still after having the entire grating removed, still have 100% dark images when the lid is closed.

OK - that's OK, the camera should be looking at the dark inside surface of the lid. The grating or DVD should bend/refract the light downward into the lens -- this is why i'm concerned about the orientation of the grating.

For a DVD, it's easy to see when the curved outer edge of the disc is at the top of the box. For film gratings, this is harder to determine, but you can try rotating it 90° and trying it both ways -- it has a directionality, basically.

I would try with the DVD first just because it's easier to know when it's properly aligned. Then upon confirming nothing else is wrong, and it's working, switching over to the grating again.

Can you upload a picture with the DVD in place? Thanks!

Thanks for prompt replies. I'm travelling now without access to the spectrometer, I'll share new photos on Mon/Tue next week.

As far as I can see that camera placement looks as it should. Going off on something of a tangent, do you happen to have a laser pointer. If you point the beam of a laser pointer through the spectrometer slit with the beam passing parallel to the base of the spectrometer when it strikes the diffraction grating it should bend down and pass into the camera lens. Probably best to temporarily stick a bit of white card over the camera lens to avoid danage to the sensor. This is why it is important to have the grating oriented correctly - the line across the grating need to be parallel to the base of the spectrometer so the diffracted beam bends down. If the lines of the grating are at right angles to the base the beam will bend to one side (well both sides actually). Does anyone have a handy drawing of the spectrometer geometry showing the light path? That might help.

The grating orientation might be the thing. I somehow didn't think about it before. I do have a laser pointer, and when I tried a few weeks ago, I was able to get something when pointed to the slit. It's just that "something" didn't look right. I think I have to check what about doing with that grating... I feel the "aha moment" is getting closer :D

Just tried it and it is important to note that what you will see is 3 dots once the laser beam has passed through the diffraction grating. One is where the beam passes straight through and then there are two diffracted beams one below the main beam and one above. And you can see the direction of the track / lines on a DVD by just reflecting some daylight off it. You will see a reflected spectrum at right angles to the lines. I'd assume the same was true for any diffraction grating. But note that the diffraction angle is dependant on the LPI of the grating. If you are using a piece of commercial grating that is not as fine as a DVD the light may not be bending far enough to hit the camera.

Quick update:

The grating orientation might be the thing.

I tried 4 * 2 = 8 combinations for the grating, and it didn't make any difference - in all cases, the camera gets entirely dark once I close the lid. I'll have to step read all the comments once again and think about what to do next...

I have also a spectrometer version for the mobile phone, so I'll what are the results with it and maybe it will help to figure out what is wrong.