Foveon colors through a prism of a spectroscope DP3M

[Stillton]

While playing with my optical spectroscope, I realized that I can cast a rainbow on a sheet on paper with it. This is not its proper use, as you are supposed to look into it to see spectra.

So, I decided to photograph it with my DP3M to see, how well it would render spectrum of sunlight. In my test, sunlight was coming through a pane of glass (aka closed window), and cheap white paper was used to "catch" the spectra.

My set up was weak as I had to align the spectroscope manually to get the rainbow to image properly, while holding a camera with my other hand...
So, ISO320 and all that "good" stuff.
I might redo it more cleanly and with white Teflon tape instead of paper, but this will do for now:



I checked it with a 405+-10nm laser pointer, and the resulting narrow band lands right where violets end on all color images above. So, roughly speaking this cut off point is around 405+-10nm.

I also noticed that there appears to be a lit area past the violet area (B100 shows it well).

My guess is that either:
1) some UV got through the glass, lit up a UV-sensitive dye in the paper. (Such dyes are used to make paper more blue optically). So, this created a glow in the visible parts of the spectrum, but it was imaged where UV would be cast by the spectroscope.
2) Alternatively, DP3M can capture some UV past 390nm.

 

[xpatUSA]

Congratulations on having the patience to use the equipment as described, and what a well-prepared presentation of the result!

Hoping for more later ...

 

[Scottelly]

While playing with my optical spectroscope, I realized that I can cast a rainbow on a sheet on paper with it. This is not its proper use, as you are supposed to look into it to see spectra.

So, I decided to photograph it with my DP3M to see, how well it would render spectrum of sunlight. In my test, sunlight was coming through a pane of glass (aka closed window), and cheap white paper was used to "catch" the spectra.

My set up was weak as I had to align the spectroscope manually to get the rainbow to image properly, while holding a camera with my other hand...
So, ISO320 and all that "good" stuff.
I might redo it more cleanly and with white Teflon tape instead of paper, but this will do for now:

Cool. I think it's interesting that portrait and standard look so similar.

I checked it with a 405+-10nm laser pointer, and the resulting narrow band lands right where violets end on all color images above. So, roughly speaking this cut off point is around 405+-10nm.
I also noticed that there appears to be a lit area past the violet area (B100 shows it well).

My guess is that either:
1) some UV got through the glass, lit up a UV-sensitive dye in the paper. (Such dyes are used to make paper more blue optically). So, this created a glow in the visible parts of the spectrum, but it was imaged where UV would be cast by the spectroscope.
2) Alternatively, DP3M can capture some UV past 390nm.

I wonder how various CFA cameras would do in this test setup.

--
Scott Barton Kennelly

Big Print Photos - Photography by Scott Barton Kennelly

Landscape and nature photography, photographic prints by Scott Barton Kennelly, an Australian photographer living in south Florida.

www.bigprintphotos.com

 

[Stillton]

While playing with my optical spectroscope, I realized that I can cast a rainbow on a sheet on paper with it. This is not its proper use, as you are supposed to look into it to see spectra.

So, I decided to photograph it with my DP3M to see, how well it would render spectrum of sunlight. In my test, sunlight was coming through a pane of glass (aka closed window), and cheap white paper was used to "catch" the spectra.

My set up was weak as I had to align the spectroscope manually to get the rainbow to image properly, while holding a camera with my other hand...
So, ISO320 and all that "good" stuff.
I might redo it more cleanly and with white Teflon tape instead of paper, but this will do for now:

Cool. I think it's interesting that portrait and standard look so similar.

I think Portrait looks a tad less saturated. I need to find that python code that creates spectral graphs from images of spectra - it should be able to show the difference.

I wonder how various CFA cameras would do in this test setup.

I have an old D5000, that I was planning on using as a comparison for my Round 2 of the test.
That, and my iPhone8 too...

 

[DavidWright2010]

While playing with my optical spectroscope, I realized that I can cast a rainbow on a sheet on paper with it. This is not its proper use, as you are supposed to look into it to see spectra.

So, I decided to photograph it with my DP3M to see, how well it would render spectrum of sunlight. In my test, sunlight was coming through a pane of glass (aka closed window), and cheap white paper was used to "catch" the spectra.

My set up was weak as I had to align the spectroscope manually to get the rainbow to image properly, while holding a camera with my other hand...
So, ISO320 and all that "good" stuff.
I might redo it more cleanly and with white Teflon tape instead of paper, but this will do for now:

Cool. I think it's interesting that portrait and standard look so similar.

I think Portrait looks a tad less saturated. I need to find that python code that creates spectral graphs from images of spectra - it should be able to show the difference.

I wonder how various CFA cameras would do in this test setup.

I have an old D5000, that I was planning on using as a comparison for my Round 2 of the test.
That, and my iPhone8 too...

I'll be looking forward to those comparisons.

I tried to do this a few years ago, but my technique was not good enough. I will do a search for the images i got, (with several Bayer sensor cameras as well as my Sigma) and compare with yours.

David

 

[Hanicka]

Do you have a bayer camera to show the difference?

 

[D Cox]

Do you have a bayer camera to show the difference?

Here is a graded spectrum filter photographed with a Sony NEX-5n.



And a DP3M:



In practice, the Sony takes perfectly acceptable photos, at least of general scenes.

Don

 

[Stillton]

Do you have a bayer camera to show the difference?

Here is a graded spectrum filter photographed with a Sony NEX-5n.



And a DP3M:



In practice, the Sony takes perfectly acceptable photos, at least of general scenes.

Don

Wow, there is a lot of teal/cyan components missing there in the sony picture, and then violets are turned into blue. Not surprising given how CFAs operate, but still. This helps to explain why Foveon colors look different and somewhat more natural - Foveon simply does sample the spectrum more uniformly, instead of just losing bits and pieces here and there.

 

[Stillton]

Part 2 has arrived. Foveon vs CFA sensor daylight spectra - Part 2: Sigma Camera Talk Forum: Digital Photography Review (dpreview.com)