Solar Spectrum with Baader grating

[Merlin66 (Ken)]

I set up a needle to make a reflective slit; used a 135mm lens with the Baader 207 l/mm grating, modified Canon 1000D, ISO200, 1/1000s
The profile of the spectrum (blue) compares well with a G2V reference spectrum (purple) - just a bit of fun.

[robz (Robert)]

Hi Merlin, ........don't mean to be a smarty pants, but I've seen similar if not better with a DVD used as a grating on solar light.

Rob.

[Merlin66 (Ken)]

Rob,
if you can show me a spectrum image from a DVD/ CD with the same resolution I'll eat my pants...smart or not!!

[sheeny (Al)]

Looks really good on the red end, Ken, but not as sharp on the blue. I'm guessing that could be due to focus. Is there any other factors that could cause this?

Al.

[theodog (Jeff)]

Nice one Ken.
Many and varied ways to get a spectrum.
Well done.

[Merlin66 (Ken)]

Yea, I was focusing on the red end...should have done another for the blue....next time.

[robz (Robert)]

Originally Posted by Merlin66

Rob,
if you can show me a spectrum image from a DVD/ CD with the same resolution I'll eat my pants...smart or not!!

Merlin, what end of your pants would you like to start with?

I have here the crudest DVD spectroscope imaginable : a 240mm long, 40mm diameter cardboard tube with a dvd slice/wedge(DVD split in to two halves, and one reflective side used) shoved in at 45 degrees (mee teenks?) at one end with a viewing hole above it.
At the other end is a horizontal, 0.25 mm slit made of two business cards sticky taped together .

Looking at your spectrum(reversed : as mine is a reflection not a transmissive one) I can clearly make out all the dark absorbtion lines that match the same positions on the photo you posted.

The spectra is more compressed laterally than what is seen in your photo, but the dark lines are crisp and very defined.
What's more is that this is a direct view, not a photograph.

Also, the sunlight source was not a super reflective needle.........it was just a white building facia outside my window.

I will try to take a photo of this(gonna be fun as the viewing hole was made with a pen!)

Here is a description of the spectra as I see it:

Starting from the violet end, is the first black line,followed by another in the blue,......... in the green : two distinct separated lines, and what appears to be two more fainter ones as well!........a fourth in the yellow, and finally another well in to the red.
I can not see the second line at the far end of the red.
Is this because it's infrared?

Rob.

[Merlin66 (Ken)]

Hmm,
Some people just don't give up easy
The telluric line in the far red is difficult visually - near the end of our sensitivity range...
Ok, the get the cotton daks out and marinate them in red wine - just incase you come good with an image

Joking aside, you may actually be getting somewhere....

[robz (Robert)]

Merlin, no problem pal, don't expect you to eat anyone's pants......even your own(marinating in wine does sound tasty though)

I know I will have to prove this so the weight is on my shoulders

All that aside..........I am VERY.........VERY! surprised at what I'm seeing...............this shouldn't be so..........in all reasoning.

Rob.

[robz (Robert)]

O.k............here are some lousy shots done with an el-cheapo point and shoot digital camera.
Even though I am a fully qualified professional photographer(retired), I pulled out of the business as film was becoming hard to get, so I never purchased a high end digital SLR.

I can say that taking a photograph of spectra with such a poorly made device and camera (a good photographer allways blames his equipment),was EXTREMELY difficult.
The camera's tiny telescopic lens had to be angled and zoomed in just right to even obtain any image at all. On top of that was trying different settings in the auto focus mode etc

The shots will show a spectra that looks ten times worse than seen through the eye............and that is not an excuse to cover up the DVD spectroscope's ''true capability''.

You will see that the far red line has failed to appear. The yellow is poor compared to visual appearnce.
I guess this is the camera's I.R. cut filter responsible for this

Anyhow.........here they are:

[SkyViking (Rolf)]

It's great to see these spectra being photographed.
I have looked at the solar spectrum countless times reflected in CD's and DVD's. I have found the best view to appear when holding the CD/DVD right up to the eye and catching the 2nd order reflection (1st is usually too bright). No slit is necessary, just use the direct spectrum from an unobstructed view of the sun and let your eye relax and focus on infinity - then you'll see LOTS of lines all the way through the spectrum. With this method I can easily resolve the double Sodium lines in the yellow part. I must concur with Rob that the visual view is far better than what the photos show (although you guys' photos are excellent). Oddly enough I have never made an effort to photograph this, but in light of your excellent results I think I might have a go soon. Thanks for sharing your results, it's very inspiring.

[robz (Robert)]

My pleasure Rolf

[Merlin66 (Ken)]

The distinct red green blue regions are due to the Bayer Matrix. I'd assume, yes, the far red may be cut-off by the inbuilt UV-IR camera filter. I use a Canon 1000D with full spectrum mod it gives good coverage from the UV to the NIR. A mono camera is even better!

[robin_astro]

Here's one I took a couple of years back using a similar setup with a Star Analyser and a 350D with a 250mm lens. I was trying to see if I could split the Na D lines. I got to about 10A resolution (AFAIK the highest resolution achieved using a Star Analyser) but failed to get a split.

Cheers
Robin

[robz (Robert)]

Hi Robin.

It's remarkable how close my DVD spectra appears compared to the Star Analyser shots.

Am I missing something here?................quite possible as I'm very new to this.

Rob.

[Merlin66 (Ken)]

Rob,
To do a fair comparison you would have to carry out a proper calibration of your spectrum and then do what Robin and I did, pull up a G2V reference spectrum for comparison.
Just look at the smaller "ripples" and how the detail matches the dips and bumps in the reference spectrum.

[robz (Robert)]

Understood Merlin.
Doubt whether the DVD will match a proper grating.

Looks like I might try one of the triple prism spectroscopes on Ebay and adapt it for use on an eyepeice and camera possibly?

[Merlin66 (Ken)]

Check out the cost of a small "educational" grating - these will give about the same performance and are easier to set up for imaging

[robz (Robert)]

Will do Merlin.
Thanks for all your help.

Regards.
Rob.