Coastal Optics 105/4.5 Diffraction Grating

[Andrea B.]

D610 + CO105/4.5 + BaaderU + Linear Diffraction Grating 1000 l/mm

f/16 for 1/60" @ ISO-1250

 

The camera/lens/grating was aimed towards the sun which was screened somewhat by a tree. I was aiming maybe 15-20° off perpendicular.

 

Conversion with color profile made for D610 + CO105/4.5 + BaaderU.

 

Conversion with color profile and white balance.

[Andrea B.]

Raw Composite before white balance

[ulf]

Andrea, I think the grating-material you are using is of the same type as the one I measured here:

https://www.ultravioletphotography.com/content/index.php/topic/2643-first-attempt-with-linear-filter-grating/page__view__findpost__p__19967

 

Then your images show the transmission performance of the grating and the sensitivity limit of your camera very well. The lens is not at all limiting.

 

Interesting to see the colurs, even if that is unique for the bayer response of your type of camera.

The faint darker bands might even give a hint of the real wavelengths, if you used the sun as light source.

http://bass2000.obspm.fr/solar_spect.php

[dabateman]

Andrea,

If your not afraid of the command line can you split the image using 4channels. I am in the process of doing that for my cammeras. Basically take a similar image as you have, then run the raw through 4channels and look at the images from each of the separate color channels. I want to see how your converted sensor sees the color.

I guess you could do that in Raw digger, but I don't know if you get an image. I want to see the visual gaps of the color channels.

 

Also, is the sun your light source? Looking at this I would say that 370nm to 380nm is very intense with the brightest signal. Indicating what I have said before that you are mainly seeing that spectral region. The transmission peak for the Baader venus filter is 350nm, but your green to yellow interface, which would be around 350nm is quite weak. But this is assuming your using sunlight and not a Hallogen lamp for these images.

[Andrea B.]

Thanks for the comments! I got the mounted diffraction grating quite some time ago from Cadmium but hadn't had a real chance to try to use it correctly. I think I messed up the first time I tried.

 

Ulf, yes, I was aiming the camera/lens towards the sun which had some screening from a tree. I'll go back and add that to the post.

 

David, yes, I can get the 4 channels from Raw Digger, so I'll do that and post. (Although I am not afraid of the command line. That's all I did for 20 years at the Labs. Still love the command line.)

[ulf]

Thanks for the comments! I got the mounted diffraction grating quite some time ago from Cadmium but hadn't had a real chance to try to use it correctly. I think I messed up the first time I tried.

 

Ulf, yes, I was aiming the camera/lens towards the sun which had some screening from a tree. I'll go back and add that to the post.

 

I think it is the same material as I measured. The same seller on eBay sells the film mounted in slide frames and in rolls. If I remember correctly Cadmium told me that he bought a roll.

I had a now scrapped project to build a simple spectrometer with the grating film-material, until I found and bought a real spectrometer.

In that design I had a slit at some distance in front of the foil to improve the resolution.

[Andrea B.]

The red channel was blown out a bit. Not unexpected.

 

Can someone help ID the bands? Thanks.

 

This BaaderU is marked HWB 325-329 nm.

 

Top to bottom: red, green1, green2, blue, raw composite (no WB), white balanced

[dabateman]

Thank you for the split channels. Not at all what I was expecting. But I haven't done my cameras yet.

I was expecting the green channel to be strongest on the low UV end and drop off as you get closer to 400nm. But you don't see that at all.

 

I hope Dmitry or Andy see this. They both know the Fraunhofer lines better than I do.

 

H Ca+ 396.847

K Ca+ 393.366

L Fe 382.044

N Fe 358.121

P Ti+ 336.112

T Fe 302.108

t Ni 299.444

 

Ok just found better table. You will want the ones with widest band.

http://www.coseti.org/9006-025.htm

 

[Andy Perrin]

They are too blurry to ID, even using my MATLAB script. Possibly the focus was not good? The bands I get from Dmitry are much clearer.

[dabateman]

Shouldn't need a script. The two on the right should be H and K. Then since linear. Just walk back.

 

Actually, knowing that. In ImageJ could set the pixel per nm scale and calculate each one.

[Andy Perrin]

It's not really linear. You are projecting onto a flat surface, which causes distortion near the edges. If you want accurate numbers, you definitely need to adjust for that. My script does interpolation between known lines, and the more lines you have, the more accurate it gets. That dodges the thorny issue of correcting for the lens barrel distortion and the projection errors.

[Andrea B.]

I was expecting the green channel to be strongest on the low UV end and drop off as you get closer to 400nm.

 

All those color-to-wavelength charts are using white balanced color. There is scarcely any green at all on the left if you look at the raw color strip. But the interesting fact is that there is some green. That for me was unexpected in the raw colours.

 

(That little bit of green is more easily seen when look at the big raw before all the resizing and smushing into the jpg.)

 

THank you for the band labels.

[Andrea B.]

Added: That might not be green. It might be a kind of dark yellow? Dark yellow looks rather olive greenish to me.

[Andy Perrin]

Dark yellow looks rather olive greenish to me.

Me too, even colorblind. (But sometimes I confuse it the other way -- I say "dark yellow" or something and then someone corrects me and says, "no, that's green!")

[colinbm]

Andrea, you need this, RSpec Explorer,

Cheers

Col

[Cadmium]

Andrea, looks good! It is green. The green is the 320-340nm range. Looks just like it should.

[dabateman]

Andrea, you need this, RSpec Explorer,

Cheers

Col

 

She already has the camera and filter, just needs the software. Here are some options:

https://publiclab.org/notes/warren/09-01-2016/calibrating-your-spectrometer-in-spectral-workbench

 

https://www.theremino.com/downloads/automation#spectrometer

 

http://astrosurf.com/vdesnoux/

 

I have visual spec, but haven't gotten around to fully playing with it yet.

 

There is also Spectrum studio by Science Surplus.

[colinbm]

You can just purchase the software...

https://store.fieldtestedsystems.com/collections/for-your-classroom/products/copy-of-rspec-astronomical-spectroscopy-software