First Light spectrum obtained with new spectrograph.

Thought I'd share this. I recently acquired an L200 spectrograph. For those who don't know this is a littrow spectrograph similar to the shelyak L-Hires instrument. One of the main differences being this provided as a kit for home build, hence it comes in at around 1/4 price. Well I was lucky enough to acquire the very last available kit from the current batch of these. I took lots of photos during the build and will write them up later.

Anyway on to the subject matter. I had a first light with this last evening. Arcturus was well up in the south-east. The following is 5 x 60 seconds and is calibrated with a neon reference lamp. I must have bumped something between taking the sequence and the neon calibration frame as everything is shifted about 7 angstroms to the red. However it still is in very good keeping with published reference spectra for a KIII type star. The domain measured was 5920 - 7000 angstroms (red to infra-red) and resolution is 1.5angstroms/pixel.

www.webtreatz.com/gallery/displayimage.php?pos=-105

Image was taken through C14 at f/10 and ST8 binned 2x2.

I'm looking forward to having lots of fun with this as the resolution R=3000 is plenty good enough to measure stellar radial velocities, classifications, determining spectroscopic binaries and even galactic red shifts.

Will post more as it happens.

Clear skies,

Dave.

I should add, the bright peak at the left is a hot pixel and not a new emission line:)

Dave - fantastic stuff.

Spectroscopy is a fascinating.
Whole bunch of new possibilities for you now.
Hopefully, as time rolls on, we might get one or two more taking the plunge in that direction and its good to see that we're going to have some local hands-on experience.

Mark C.

Well done Dave. Serious scientific capability there.
What is the wavelength range of the spectrometer? If it goes below 8000A you might be able to get some chemical data also (i.e planets, bright nebulae, comets etc..) although you will be limited by the glass transmission on the corrector plate.

John, The grating is blazed at around 550Nm so it is efficient right from UV to IR. Observing chemical lines in planetary atmospheres is very definitely on the cards.

Dave,

VERY nice work and good for you! This is something which has been on my mind for some time and I will certainly be following in your footsteps much sooner than later.

Can you provide a link surrounding the spectrograph?

Congrats once again!

Anthony.

Anthony,

Here is a link which highlights a users L200 on the bench;

www.stargazing.net/david/spectroscopy/SpectraL200Bench.html

Unfortunately it is not a commercial spectrograph, therefore there is no webpage. The kit is produced and sold by Ken Harrision a well known amateur spectroscopist. He produced this so that interested folk could have a high quality slit spectrograph at a reasonable price. The cost was 880usd. This conpares to about 1/2 of some commercial units.

Unfortunately Ken's run was small and I beleive that there is none left Maybe Ken will run off another batch. I'm sure he would if there was an interest.

For more info on this visit the astronomical spectroscopy group on yahoo;

tech.groups.yahoo.com/group/astronomical_spectroscopy/

Some details of th unit. Its a littrow design so there the same lens is used for collimation of the incoming beam and focusing the spectra. The grating provided is 600 lines/mm giving a resolution of R=3000. Wavelength adjustment is provided via a micrometer and the slit can be opened or closed from zero to about 1mm in VERY fine resolution

If anyone is interested in learning more about spectroscopy, Ken Harrison has just published a great book on the subject, including theory, design and operation and lots more besides.

If Ken evr does make another batch, I'd highly recommend the kit as long as you don't mind a bit of spraypainting and assembly.

Hi Dave,

Congratulations on entering the spectroscopy field. You'll have great fun in imaging spectra. Not many amateurs carry out observations in this field. Its got easier now with off the shelf systems that are affordable and user friendly.

I entered the field about 12 years ago having bought a 'Rainbow Optics'
grating for $200. Worked really well for spectra of bright stars. Resolution at 200 grooves/mm. Certainly recommend the Rainbow Optics' as a starter. Once you get the bug you want to adventure into a wider range of candidates that may be difficult to obtain spectra.

However, because I was interested in wide field spectra for comets and emission nebulae, I couldn't find anything in the market place off the shelf. So, I designed and built a wide field spectrograph.

It's FOV 3 deg x 3 deg (resolution 400 grooves/mm) . I designed it to provide a new capability for measuring the spectrum of the sky across fields of view much larger than the full moon as compared to the conventional narrow systems. The instrument uses a high speed optical system to form an image on the entrance slit of a matching stigmatic spectrometer, this then disperses the spectrum of a strip of the sky onto a CCD camera. A separate imaging system is used for pointing and tracking. The system is very heavy at about 40 kilos. It's excellent for imaging comets and emission nebulae. I have a paper published providing the details of construction and application called

'A new wide-field spectrograph' Proc. SPIE 5492, 1290 (2004)

I also have a Zerny Turner design for narrow FOV at 600 grooves/mm. Because it is a heavy construction I am using a fibre optic feed from the eyepiece holder exit of the telescope.

Since then, I have dismantled the parts of the wide-field spectrograph and I am applying it for a solar spectroheliograph. The idea is to tune into hundreds of wavelengths. So far half built. This project has become more complex in building.

Eamonn A

Eamonn, I would also second your racommendation about the Rainbow Optics unit. I managed to get hold of a Star Analyser from Paton Hawksley. It's 100 l/mm blazed to the first order. This one costs 87stg. Combine it with a 3deg wedge prism from edmund optics for around 40eur and you end up with a capable unit for low resolution spectroscopy, without the big price tag. A great idea for someone on a budget or whos mount/scope might not be up to the demanding requirements of a slit based spectrograph. You can still measure some radial velocities and lots of other useful observations.

I look forward to having a chat with you about this soon.

Dave/

Dave,

I bought the Rainbow Optics (RO) as a complete system. ie. grating plus spectrum-widening cylindrical lens for $200. It has advantages over the wedge prism type. Unlike a prism wedge, which distorts a spectrum by spreading out blue light more than red, this grating creates an undistorted, constant dispersion across the entire visible spectrum.

I was aware of the Paton Hawksley grating, but the res was lower. RO are still making them for $249, which is good value.

Eamonn A

RO no longer sell outside of the USA

Hi Michael,

I remember awhile back your interest when I spoke to you about exploring a new concept of imaging the Sun by obtaining multi-line observations and two dimensional spectroscopy, which can reveal the dynamic behaviour at different locations and wavelengths. By obtaining 2D spectral images with spacial info plus wavelength you can end up with 3D Sun at multiple wavelengths by designing a solar imaging spectrograph.

In order to answer your questions there are so many other aspects that are integral within this type of design

The Solar imaging spectrograph uses a heliostat type configuration. It has been designed to observe solar spectra in the range from 3000 to 10,000 A with a spectral resolution 0.2 A/mm. The system is composed of a 35cm diameter heliostat with a 20 cm achromat lens of f/16 (3.3m focal length), spectrographic system has a 400 groove/mm grating, and a 1k x 1k CCD detector.

The system consists of four elements, a heliostat, optical system, a CCD camera and software. The ray from the heliostat goes through a 20 cm achromat via the cut off filter (CF). However, the cut off filter only accepts the radiation covering from 3500A to 7000A. It can prohibit the optical system from heating up by cutting off the infrared and ultraviolet rays.

The development of the system will be able to obtain three-dimensional imaging spectrograms by using a scanning mirror in front of the spectrographic slit. The scanning mirror concept rotates by one step, the solar image on a slit moves by for example 70 microns, which corresponds to a width size of the slit. The imaging requires a lot of image frames for a single imaging spectrogram. However, it provides the opportunity creating spectrograms throughout a wide range of frequencies.

The slit also has the unique option if required of both a bilateral movement in sync with the rotary stage. This means that the slit assembly has the added option of a lateral movement. See Notes

The whole optical arrangement involves two separate buildings. The first building houses the heliostat with its own tracking system. The rays are projected horizontally from the heliostat to the second building, which has the optical system (Spectrograph). In between the two buildings is the movable achromat on motorized rail. The whole structure is about nearly 30 feet in length.

Status

The 35cm heliostat on a fork equatorial mount is near complete.
The mirror(1/4 lambda)I made awhile back. The mount uses 30cm dia. drive gear
The electronics/controller are complete for the mount.
The 20 cm achromat is complete. Used as the main periscope lens in the Hunter Killer submarines of the Royle Navy(made by Barr & Stroud,UK) High res lens.
The second building is complete.
The rail parts are complete and movable truck to hold lens assembly.
First building the foundations and walls are complete. Half built roof.
The rails from both buildings are complete. 30 feet in length.
The scanning mirror – mechanics are complete are designed and built, mirror needs coating.
The scanning mirror requires stepper motor-encoder configuration
The scanning mirror will require software development linked to slit.
The spectrograph bilateral slit and microcontroller and software is complete.
The grating is complete (Richardson Gratings, US).
The grating rotary table is designed and built, complete with microcontroller and software.
The collimator is built and working.
The receiving lens is complete and working

Note: The diffraction grating ruled area size is 102 x 128 mm. It is a 400-groove/mm plane reflectance grating blazed at 551 nm with a nominal 6.3-degree blaze angle. The grating has 90 per cent efficiency at its blaze angle and in first order from 5000 to 11000 Ångstroms the response stays above the 50 per cent grating efficiency points. In diffraction grating instruments such as this one, the first order image at any wavelength contains light from half that wavelength in the second order. When, for example, the spectrograph is to reach a maximum of 10,000 Ångstroms in the first order, wavelengths less than 5,000 Angstroms must be excluded.

Note: The spectral coverage of this instrument is between 300nm and 1000nm. Its optimum efficiency is in the 300-450nm range.

Note: It projects the incoming light through a horizontal moving slit assembly onto a reflective grating based on a rotary platform that is synchronised with the slit mechanism. The slit width is adjustable, as is the case in conventional spectrographs.

Note: An important part of the design is the lateral movement of the entire slit assembly (in addition to the movement of the slit itself), so that the narrow beam passing through the slit will reflect off different parts of the diffraction grating and be received by the camera in a scanning mode.

As you can appreciate there is a lot of work involved.
However, by designing and building yourself is very satisfying.
If everything goes well this year I may have first light.

Eamonn A