First light for 200mm Littrow

Finally managed to the the 12" LX200 and the Littrow to actually image a star spectra ( Vega)
A series of 4 sec exposures as the drive was not working well ( see comments about balance below).
Found out quickly, even with the safety bracket in place that the metal dew shield ( 1200gms) at the front doesn't balance 1500gms of spectro hanging at the back!! The Dec bearings are so stiff ( the original nylon ones) it's very difficult to tell when the balance is correct. You only really find out when the Dec drive overloads and doesn't work!!

Must remember to re-set the grating micrometer to the ZERO position before trying to find a star image!! Must have wasted 15min before I realised the problem!

Also found difficulty in getting a focussed star image on the slit. I had the 32mm Pl in the beamsplitter with a diagonal; could n't get my head into position otherwise ( old age!) and found that when eventually I got a reasonably focussed image on the slit the eyepiece showed it well out of focus. Guessing an additional 25mm or so spacer needed between the beamsplitter and the spectro.
Two options:
Use the QHY5 guide camera only for aquisition and drop the diagonal. Need to try it out to see what the FOV is like. I did manage to position the star on the slit just by noting the star position on the finder cross wires, so may be doable.
Second option is to add a spacer in front of the Spectro to accommodate the diagonal distance. This would mean the spectro would sit even higher on the back end ( BTW at the moment it's impossible to use the guide scope; not enough clearance at the back; either remove it and rely on the beamsplitter ( good option!!?) or relocate it further towards the front end....balance issues?) and making up a new safety bracket ( no big deal)
I'll try the QHY5 first... see how we go.

It's also difficult to see where the star is relative to the slit.... need some sort of back lighting (??) to illuminate the slit edges, and then should be able to see where the star image is sitting, maybe a small red LED in the body of the spectro which can be switched on briefly....

Other than that, the Canon 350D seemed to record a spectrum in a 4 sec exposure!!
I got about 10 exposures; now need to figure out how to combine them before applying Vspec for analysis. Didn't have the neon connected for these trials. I'll wait until I get the 3V supply sorted out.

The dew shield and heater kept the front end about 1.5 deg above ambient and the corrector seemed to be clear ( total observing time about 2 hours); the benefits of the Argos TSO ( Tin Shed Observatory) were appreciated!!!!

Near Disaster!!

While fitting the Littrow, with the Cube Beamsplitter to the 12" LX200, the 1 1/4" fittings rotated and dumped the spectroscope onto the floor, via a couple of bounces of the edge of the table!!!
You know that feeling you get when you cut yourself with a sharp knife??? Just like that!!
A lot of bad rattling noises from the spectroscope.....
That was on Friday, the 26th ( double the 13th!!)
Pulled the spectro apart and found the collimating lens had been knocked out of the holder and it had dropped forward onto the grating!! Some slight scratches on the grating, but not too bad.
The slit and prism etc seemed OK.
Took the best part of the day to re-set and re-glue the collimator, a mixture of using the laser beam and Cheshire eyepiece.
Today ( 1st Oct) finally got the chance to check the focus with the Canon 350D body.... looks OK.
So... I've already made up a holding bracket which will positively clamp the body of the spectro to the Meade scope. This MUST be used all the time!!

200mm Littrow Spectroscope

The Classic spectroscope I built in 2006, although providing great experience and useful results, was not perfect. My workmanship let me down and there are remaining issues of camera attachment and grating movement.

I spend some time making up a stepper motor drive for the grating; works well, but I still wanted a more compact, lighter version.

I've therefore built a Littrow version with a 200mm collimator and micrometer adjustement of the grating. I've also made up a couple of grating holders and purchased a new 2400 line per mm grating ( Now have 600/ 1200/ 2400 gratings)

Incorporated a neon reference lamp ( Chris Hyde has offered to make up a low voltage driver circuit - make it easier, and safer!)

Found there were a couple of undocumented issues with the Littrow design:

The inclination of the grating causes the image of the spectrum to move down the CCD as you go from zero order to red. This "slant" is caused by the inclined cylinderical curve that the grating follows. If not corrected, the spectrum can easily move off the CCD chip entirely.

The way to address the problem is to slightly rotate the grating in the holder, I ended up about 2 degrees rotation. This averages the movement of the spectrum, so although there is still some up and down movement, it's pretty well centred.

Having rotated the grating you also have to rotate the slit to maintain alignment!!!

I also found the getting the neon light into the slit, at the same time as taking and exposure, was not easy. In the LiHiresIII design, the lamp is moved infront of the slit between exposures ie on a different frame. I didn't like this idea; depends on the grating/ CCD not moving relative to the spectrum image.

Ended up using a small 9mm prism to direct the neon into the top half of the slit. Now I can get a reference image at the same time.

The documentation of the design and construction is on the project page of IceIn Space.

http://www.iceinspace.com.au/index.php?id=63,500,0,0,1,0

Earlier this month I purchased a 1 1/4" Chinese cube beamsplitter to replace the modified Meade OAG.

The hope is to get getter alignment with the star, and brighter images. Not tried yet.

Also invested (!!) in a QHY5 guide camera, should be more sensitive than the webcams or the LPI.

25 th September already!

Don't know where the time has gone. Since last posting I've been busy with a few projects. Need to sit down and do some documentation.
Weather has been terrible, so very little actual observing.

Direct Vision Spectroscope- LaFayette #F-359

Just got this wonderfull spectroscope from Ebay. The price was a steal!
In original condition, with its original blue velvet lined box case and Instruction sheet.
This is a jewel! Made in Japan, "Atago Optical Works Co, Ltd" I think in comes from the late 1950's.
A well finished satin chrome body with a heavily knurled ring on the slit mechanism; This rotating mechanism opens and closes the slit and is very smooth, as is the focussing tube.
The body is sealed with what looks like a small optical window infront of the slit and the cylinderical eyepiece lens.
Looking at the solar spectrum, it's clear bright and pretty wide ( much wider than the image in the GOTO or the Surplus Shed D-V's) The magnesium triplet and sodium lines are easy! Infact you do get the impression that the sodium lines are actually split!!

Projects in Progress

Here we are in Feb 2008, and still have some interesting projects on the go. The design of a cheap, effective ERF ( Energy Rejection Filter) to use on the Genesis 4" telescope is #1 at the moment. Based on a UV-IR filter from ROSCO, Sydney, Australia and a #25 Red from Surplus Shed. The etalon filter has been removed from a PST and adaptors made to fit the 2" focusser.