To continue looking at EBAY.com and what is there. I also see this
day that there are some GEM scopes. I do not have one of these and don't think it would work on a telescope.
I do see today a scientific spectroscope that has the collimating lens and the prism
or grating holder and a focusing lens. This is the table top unit you might have used in high school or colllege to do minimum
deviation of a prism. This is bulky and will not mount on a telescope very easily. However you can feed this scope with a
fiber. Buy a 50um upto a 500um glass or plastic fiber about 10 feet long. Place one end of the fiber in your telescope
and align the star or galaxy so it focuses on the end of the fiber. Place the other end of the fiber into the spectrograph
collimation slit. Voila, very good images of colors and lines and stuff. But you will find it is very hard to keep a star
image of 20 um across on the end of a fiber.
I see one more Direct vision device on Ebay.com. This one has a built in wavelenght
scale. It appears at two tubes held together on one end. This unit works very well for most terestial light sources. You can
see the lines of Mercury, Sodium, Neon, Argon, and flouresence lines by using this spectroscope. Again it takes a fairly
bright star to see any line details since the continious spectrum of the star will usualy over ride the brightness of any
lines.
There is also an eyepiece spectrograph. You can buy this at most telescope accessory
stores. This has a device that slips over an eyepiece, say a 20mm FL eyepiece. As you look at the star there is a cylindrical
lens that can be focused and rotated to smear the spectrum into a sort of line. Againt this does not usually show much
detail and the bright continuom of the star over rides any details. If you look at nebulae you usually are disapointed
unless you have atleast a 16" scope to collect more photons.
| Rainbow Optics Spectro Grating and Cell Design |
|
| www.starspectroscope.com to see this device |
| Rainbow Spectro Lens Adapter picture |
|
| Spectrum of Sirius Star by Christain Foy |
Enter supporting content here
It may now be time to look at stellar Classification of stars by using spectrographs.
There are on the market a few fancy spectrographs that will bolt to the back end of your telescope and give
you expensive but high quality spectro capabilities.
The best known units are the SBIG which comes in a auto guide version at a resonable price even for an amateur.
I will insert some real spectrals when i get a chance.
Please go to the SBIG.com site and or do a GOOGLE search on sbig spectrograph and you will find many articles.
| SBIG.com DSS-7 Tracking Spectrometer Box |
|
| This bolts right on the back of the telescope |
| SBIG 1 to 5 Angstrom per pixel image |
|
| Spectrum of M104 using the SBIG DDS-7 |
There are several European spectrographs that are built for amateurs. You can build you own from parts
or order a kit.
The spectrograph usage is probably the number one driver for the cost, weight, resolution abililty, ease
of use, and results required.
Spectrographs come in several varieties.
One is the direct prism type discussed above.
Second would be a grating of transmission or reflection which requires extra parts to get the star light
into the device and the image out.
Third might be the Littrow type spectrograph. This is more compact but can be heavy and large to hang on
the back of a small telescope. The Littrow method uses a standard camera lens as the collimator of the star light. The
light passes out of the lens to a grating, prism or Grism spectral dispersing element. The spectral light reflects back into
the same collimating lens and creates a spectrum at focus that is slightly off axis from the input star. You can view this
image or photograph it.
An example is this LHIRES III project kit spectrograph.
| LHIRES III Project Amateur Spectrograph |
|
| Used directly on the back end of your telescope. |
| LHIRES III spectra showing absorption lines |
|
| Part of a spectrum of the SUN |
Here is a quote from the web site on the LHIRES Kit made by Shelyak
Instruments. The web site location is http://www.astrosurf.com
"Christian Buil and André Rondi took the first key steps
in attaining spectroscopic resolutions above R = 15,000 for amateurs, with the introduction of the LHIRES-type spectrograph.
Based on this design, François Cochard has developed a limited-production version of the Lhires III Littrow-design. François
validated many of the technical solutions possible in August 2005 during the first symposium dedicated to amateur astronomical
spectroscopy at the Observatoire de Haute Provence. The Lhires III
spectrograph is a high performance instrument with a spectral resolving power up to 17,000. It was primarily designed for
instruments with focal ratios in the range f/8-f/12. (For those amateurs with faster telescope systems outside this range,
you should check beforehand that a Barlow lens will still give you enough mechanical back-focus - verify this before ordering
a kit!). The Lhires III can be used with several types of CCD cameras (Audine, SBIG ST7/8, Starlight Xpress...) or Digital
SLRs (e.g. Canon Digital Rebel, Nikon D100/D70...). High-Resolution stellar spectroscopy has now become a reality for amateur
astronomers thanks to the Lhires III and will open the door for amateur contributions to studies of bright novae, non-radial
pulsations within stars, binaries dancing around each other, evolving gas clouds around Be stars, and so on..."
Ok, a fourth type of spectroscopy is to use a shallow prims in front of your telescope. A large
prism about 6" or larger is cut from a block of glass. The prism will have an angle of 2 to 5 degrees. The star
light passes through the prism is dispersed and passes to your focal plane as a bounch of stars smeared spectra.
They use the on many telescopes, especially refractors, to do radial velocity and star stellar classifications.
This prism will be costly, large and heavy.
If you use any glass type prisms to make a spectra you will have a hard time reducing the image. The spectra
is non-linear and will have many image qualities that you have to calibrate out.
I looked all over google for an objective prism picture? I found none.
Now we are getting to more sophisticated spectrographs. The use of narrow band filters is common. You can
put in an H-alpha filter and photograph your nebulae for better results.
There are also interferometer spectrographs. These count fringes of the colored light. These are not easy
to use and require extreem temperature control. So we won't use these types.
Finally i would put the fixed bench top spectrographs at the bottom of the list.
These you will have to mount on a solid table, feed with your telescope coude output or feed them with fibers.
This is a nice clean way to get some spectrographs. All you have to do is bench mount your spectrograph.
The fibers will be their own slit at a fixed width, well diameter.
If you place mulitiple fibers at the focal plane of your telescope you can pick up many objects at the same
time.
Each fiber has to be separated from the bundle and stacked on top of each other in a line.
This way you get a spectrum out of each fiber that is separated by some small distance.
One of joe's spectra boxes is a Jarrell Ash 82-000 spectrograph from the 1960's. This box holds the
grating, a single collimating and image 6"f3 mirror, and the fiber input port and CCD output ports. Using an old pre-designed
spectral box will speed up your design. This unit has an electric scan device that allows you to rotate the Grating at a slow
rate to move to different parts of the spectra.
| Jarrell Ash 1960's spectrograph box |
|
| Get and old box and add your own parts. |
| Jarrell Ash 82-000 model Monochrometer |
|
| JA is being modified to work with Fiber Input and other Gratings |
I am modifing an old Jarrell Ash 82-000 Spectrograph box. I got the
box with no parts. I found a commercial telescope that has a 6"f3.5 primary mirror. You can throw away the
other parts or use them on a good telescope. I tested the mirror probably made in China, the first 50% was spherical, the
rest was a turned edge to make it look like it is parabolic. The overall figure of this mirror was very poor for a commercial
figuring job. The mirror is now remounted into the JA 82 mirror position.
Some day i need to refigure this mirror to true parabolic to help the image. The idea is that the
abberations at the input are canceled by the abberations at the output! This is some what true but since a grating is
inbetween the input and the output the output image is very irregular. The caustic of the image goes from a line, inside focus,
to a round fiber blurr, to a horizontal line outside focus. This is all due to the collimated light leaving the grating
at non-coaligned angles to the primary mirror. Only one wavelenght really matches the refelction angle from the grating back
to the mirror. All the rest of the wavelengths are off axis and there fore make poor images at the output.
I plan to use the spectrograph with an F10 LX200 telescope feeding a 50um polymicro fiber about 10
feet long. I will be using 4 fiber sizes all mounted next to each other in a vertical plane. At the telescope an X-Y
stage will allow the positioning of the fiber of choice, depending on seeing and object size, so that the telescope focuses
into the fiber. Part of the FOV of the telescope will go to the ST8 tracking CCD camera.
The other end of the fibers will be arranged in a vertical position at the focus input to the 6"f3 mirror.
Two more smaller fibers will be added above and below so that standard light sources can be illuminated into the spectrograph.
Finally an HX916 starlite express camera will perform the spectrogragh image collection. Data reduction
is by Vspec which is a program available for free from France, at WEB valerie.desnoux.free.fr/.
The JA 82 has a motor scan device so you can center any part of the spectrum you wish to collect.
The resolution of the device is dependent only on the number of Gooves/mm * the Length of the Grooves * the Center Wavelength
of usage. Using a 1200 g/mm grating with the 6"f3 i will get about 0.1 Angstrom resolution, 0.01nm or .00001um. This
means the spectrum is streched over about 30" in image space.
If you change to a 150g/mm grating blazed for 500nm the resolution will drop to about 1 Angstrom and the
spectra covers about 30mm in image space. The HX916 CCD is only 8.7mm long or 1300 pixels, so it will be able to do
spectral work in portions of the spectra.
| Grating Mount Holder for JA 82 |
|
| Aligning the Grating properly is very important. |
I have found that after the collimated alignment of the Ebert-Fasie Primary mirror so that the input fiber
point is mapped to the output camera center that the grating also has to be aligned.
The holder for the grating must allow for the tip-tilt of the grating in and out so that the spectrum falls
along the center line of the primary mirror.
Secondly the grating gooves must also be vertical. To align the grating you need some adjustment screws
to allow tip-tilt, and a rotation stage to allow you to rotate the grating in small angles so the grooves are vertically orientated.
| Fiber Combiner, Fiber input and CCd output |
|
| The JA82 need to be calibrated by light sources |
The JA82 will need some calibration for each grating you might use to obtain your spectum. The JA82
has a counter on the side that counts in Angstroms when you rotate the grating. The design grating for the JA82 was probably
an 1800 g/mm unit. I am using a 1200 g/mm and i get about 0.8A per count when i rotate the grating. This will also depend
on the primary mirror and the image off sets.
One problem is aligning the Mirror and the Grating so that the tip end of the fiber input is at the actual
focal distance from the primary mirror. You will also want the output image to fall in the same plane as the input fiber
tip.
I have not found a good way to perform this alignment. But, what i did was make a par-focal eyepeice
so that the CCD image plane and the eyepiece coinside. Then make the fiber holder long enough so that you can slide the holder
in and out of the input hole. So, i adjust the fiber so i get a round image at the output plane. Then measure the distance
from the fiber tip to the housing, and see if the eyepiece focal plane is the same distance out from the output beam hole.
Adjust tell they are the same distance, then secure the fiber input holder.
In the picture i show an audio fiber combiner/splitter. The funny shapped plastic thingy.
This can be opened by prying the case pieces apart. Inside you find two 1mm plastic fibers with ferrel ends. You need to glue
the ferrel ends to the plastic fibers. After that you can grind the 1mm plastic tips and polish the tips so you get really
good through put of the light. Put the unit back together and you are ready to combine two light sources.
I use a 532 green laser pointer and a 650 red laser pointer as the light sources. These are LED narrow band
laser diodes, so the spectrum out of these sources is only about 20nm wide. These make good markers for the green and the
red end of your spectrum.
I use fiber patch cords, 62.5 um core size, to input two sources. You have to use a larger output fiber
to collect from the two 1mm fibers to go into the spectrograph. Now you have some calibrated light to test your
grating.
You can now rotate the grating using the hand crank tell the spectrum colors are horizontal.
Besure the CCD is horizontal also.
Home polishing of fiber ends. This technique will do most fiber or plastic ends. Besure the
fiber is glued into the ferrel that holds the fiber.
1. obtain some 1000 and 1500 sand paper. If you see any finer grit paper greater than 1500 buy a sheet of
that also.
2. Place a piece of the 1000 grit paper on a hard flat surface facing up. Use a hard surface like flat stainless
steel.
3. Hold the fiber Ferrel vertically and in a short left-right and circular motion grind the fiber tip tell
the glass or plastic fiber becomes even and flat.
Continuse with the other finer grits, 1500, 2000, 2500..
4. Obtain a Dremel hand machine. Obtain the small polishing
pad and mount it on the Dremel.
5. Obtain some aircraft Novus Plastic Polish agent. This has some very find grit imbedded in the liquid
so it will polish.
6. Place some of the polish on the Dremel Pad and let it soak into the pad. Now turn on the Dremel
at slow speed and with your other hand press the fiber tip up against the pad with a light touch. Move the fiber tip back
and forth to polish the whole end of the fiber.
7. Using a Kellner type eyepiece or magnifier 10x loope and view the end of the fiber. When you do not see
any scratches or pits from your sand paper grinding then the end is polished as well as it will get.
8. Do the other end of the fiber also to be sure it is polished.
9. Install and test the through-put of the light.
| One method to fiber feed from a Beam Splitter |
|
| You loose maybe 50% of your light |
| A fixed 1/4 meter CVI specctrograph |
|
| Plug your fibers into the input SLIT and get spectra |
There is a company that makes and sells a fiber pickoff prism or diagonal with a small hole
in the middle. However I can't find them at this writting.
Here is a picture of a single fiber pickoff i made using an old diagonal holder, a BoyScout
stainless signal mirror, some glue and plastic.
I purchased a 62um patch cord fiber from Edmund.com and a grin lens in an FC connector to
use in collimating the output of the other end of the fiber.
Cut the BoyScout mirror into an oval to replace the diagonal inside the 90 degree turn mirror.
Drill a very small hole in the center of the BoyScout mirror at the center. The hole must be drilled at 45 degrees so it is
round when the star light passes through the hole. The mirror reflects the rest of the light to your eyepiece.
If you have more time you can drill a small hole through the middle of the diagonal glass
mirror, very carefully.
I glued to the back of the Boyscout mirror a small plastic piece cut to hold the fiber connector.
I removed the FC connector outer case and just used the ferral that holds the fiber. I inserted the fiber ferral into the
plastic holder all the way up to the hole in the BoyScout mirror.
The trick is to get the telescope to track with the star focused on the end of the fiber,
through the hole of the diagonal.
On the other end of the fiber you can run the light into the Grin lens collimator, then into
a prism for direct eyeball viewing.
I used a DVS prism assembly to look at the spectrum. Here are pictures of the setup. I will
try and take a spectrum soon.
| Telescope Diagonal Fiber Pickoff unit |
|
| Out put o the fiber goes to a DVS in this model |
| Fiber pickoff made from old 90 degree diagonal |
|
| Note the plastic piece glued to the mirror where fiber picks up the star |
A crude spectrograph can be made using a DVD or CD that has all those small equally spaced grooves.
There is an article on the web at this site about WPO spectra.
home.freeuk.com/m.gavin/solaspec.htm.
| The WPO Littrow spectrograph from there web site. |
|
| The CCD is on the right, the littrow lens and grating on the left. |
This is not the end of the trail for spectrograph and input methods from a telescope.
We will need to look at the eyeball resolution of the rods and cones to determine backwards who much resolution
power your spectrograph would require for you to eyeball H alpha lines by direct viewing through a telescope?
Softwares for visual spectrocopy reduction:
I have not tried all the available softwares as yet. But i have played with Vspec by valerie.desnoux.free.fr/
in france. This is a windows program. Down load Visual Spec and install then go get the update and all the TOOLS and additions.
There is a very good tutorial shown on the left side of the Web page. Down load all 10 chapters and have
fun reducing your spectra.
Other software that does spectral and CCD image conversions are:
1. Maxim DL
2. IRAF you need UNIX system to run IRAF
4. Astro Art
5. IF any one has used another program to analize your spectra please email me so i can check it out.
joeastro@aol.com
|
