High Resolution Spectroscopy

This post isn't really about Astronomy but it's definitely related to the Rainbow Optics diffraction grating I bought last year.  Plus Atomic Spectra is just so cool that you can't not like it!

About six months ago a friend of mine gave me an article he wrote for the Journal of Chemical Education explaining how to build a high resolution spectroscope with materials you find around your house (with one exception). The construction process wasn't particularly difficult, but my meager woodworking skills meant it took a lot of time.  Eventually I asked one of my students to help me since he was in the middle of a woodshop course at school. 

The spectroscope itself is fairly simple.  Its a Littrow-type spectroscope that contains a single slit for light to pass through, a mirror, a lens, a high resolution diffraction grating and a focuser/lens.  After a few months I tweaked the focuser a bit so I could use a camera with it. 

The photo below is taken directly from the article (Vanderveen, Martin & Ooms, 2013) and shows all the pieces necessary to build the spectroscope.
The basic parts list as well as the approximate cost is below:

•  1/2" plane wood ($15)
• Screws, nuts, bolts of various sizes ($5)
• Knife or Razor blades ($5)
• Plane mirror ($5)
• Collimating lens ($15)
• Diffraction Grating ($130)
• Focuser ($20)
• Eyepiece ($15)

The spectroscope operation is fairly simple.  Light passes through a slit created by the two knife blades.  It is reflected 90 degrees by the plane mirror and travels through the Collimating Lens (I used an old photocopy lens).  It strikes the reflecting diffraction grating and is sent back through the lens and out to the eye piece where the spectrum can be seen or photographed. In actualilty putting everything together was a bit more challenging then it sounds; the biggest difficulty was getting the light rays to strike the mirror and diffracting grating at the right angle so it missed the edges of the lens and was sent back straight through the focuser.  All it took was a bit of tweaking but it ended up taking a lot of time.


Visually observing spectra was dead easy. However photographing it proved to be quite the challenge.  At first I was set on using my DSLR camera but that proved to be untenable.  The camera body was simply to large and in combination with the focuser I was using couldn't get the chip close enough to the lens inside the spectroscope to properly focus.  But once I switched to my Lumenera camera, which has a much smaller body, it was a breeze.  In addition to imaging the spectrum seen through the spectroscope I used the program RSPEC to further analyze it.  After some basic calibration it was clear that this spectroscope has a very high resolution.

 This is a calibration spectrum I took of a Compact Florescent light in my kitechen Despite other abient light from the windows and virtually no processing its very easy to identify several elements in the spectrum. 

Below my spectrum is a laboratory refrence of a CF bulb.  As you can see its very easy to identify the peaks!

Once the weather clears up I plan to take the entire set up outside and see if I can pull the Fraunhofer lines from the solar spectrum.  See! I told you there was an astronomy bent to this!

More of the Moon

I don't know why, but lately I've been extremely interested in lunar and planetary imaging.  Using my Lu135m camera I've managed to capture some great images of the moon. The imaging chip in the Lu135m is 1/2" and when pared with my C11 has a very small field of view, around 5' x 7'.  This is about 1/4 the diameter of the moon which means I'd have to take about 20 pictures to  cover the entire moon.  Even a waxing/waning moon would be more than a 12 photo panorama. 

That's exactly what I did.  I started with 2000 frame images that I stacked in Registx. And then needed 12 or 14 images to cover the entire moon.  Simple multiplication gives over 24000 frames.  It ended up eating up a fairly sizable portion of my hard drive.  But the results were pretty spectacular.

 

 

After some great lunar images I turned my attention to Jupiter.  Unlike the moon, a great image of Jupiter requires a colour photo.  This is where the Lu135m gets a bit tricky to use.  Its a monochrome image so to create a colour image I had to take a LRGB frames (2000 frames each) and combine them using Nebulosity and GIMP.  

The images all turned out quite nicely.  I especially like the fact that in the image of Jupiter you can see not only the Great Red Spot, but also two of the Galilean moons.  Hopefully there are more clear nights in the future!

Years of Improvement

During the past few months I've finally tweaked, pulled and prodded my telescope into a nice, useable research tool. The biggest issue was finally resolved about a week ago when I got my autoguider to work.  The EQ8 apparently had a software glitch in the firmware that doesn't let it guide for more than about 10 minutes.  However once I updated the mount's motor control software it worked like a charm. 

The timing couldn't have been better; my favorite winter constellation has started rising around 9:00 pm (Orion!). 

 

 

OIII - 2 x 600s

So over the last two weeks I trained my Esprit 100 mm on Orion for hours using my new Monochrome SBIG 2000XM. Since I'm imaging from Suburban Edmonton I'm basically limited to Narrowband Filters.  I'm not quite done, but I've gotten 20 x 10min HA.  I'll need a couple more nights to get comparable OIII and SII images since I only have 2 x 10 min of each of them.

SII - 2 x 600s

The images on the right are the result of stacking, dark and flat reduction and some basic curve stretching.  They were stacked using Deep Sky Stacker and Stretched/Aligned using Nebulosity. 

Photoshop is next on my list of software to get but I'm not a fan of their decision to go to a subscription service.

HA - 20 x 600s

For anyone unfamiliar with LRGB processing, each of the frames is taken through one particular filter at a certain wavelength (HA - 656.28 nm, OIII - 495.9 nm, SII - 6730 nm).  These images are then aligned and combined in an LRGB image.











I used the Hubble Colour Palette which maps the SII frame to the Red Colour Channel, HA to Green and OIII to blue.  The result is the image below. Its a bit noisy and lacking in detail in some areas because of the low SNR of the OIII and SII images.

LRGB Orion Nebula

Experimenting with Long Exposures

Having finally worked out 90% of the bugs in my observatory I've begun trying some long exposure narrowband imaging.  Until recently all my exposures were less than 5 minutes or less.  Recently I've been experimenting with 10 - 30 minute sub-exposures.  I've noticed that while my tracking is good its essential to have a rock solid autoguiding.  And the payoff it great.  Even from my heavily light polluted urban locale I can still get exceptional detail out of my images.

Over the past month or so I've been imaging a few different targets.  First was NGC 6992, the Viel Nebula.  I started with mostly HA but then realised the signal strength was pretty low; I'm still trying to figure out why. I'm not sure if its the camera quantum efficiency drop off, the filter or just the nebula.  Anyway, I ended up taking about 2 hours of OIII along with 30 minutes of HA and SII.The result is below:

I plan on returning to the Viel at some point but for now IC 1805 is in an excellent location for some imaging.  So despite some persistent clouds and an issue with my autoguider I managed to pick up 15 x 900s OIII exposures. Since I didn't take any HA or SII images yet the image is monochrome.