I've had no success getting Maurice Gavin's WPO design to work for me. It's a great concept but the available back focus is limiting.
I'm re-building my unit to use a 55mm f 4 collimating lens in a 60mm square box ( similar to the Classic). This will give a compact arrangement and make it easier to use on the Genesis/ ED80.
Photos to follow.
Hi Ken,
I've had no success lately on any of the projects with varying spectro designs - been totally slammed with work so far this year...
Managed to get the SA100 located in front of a 135mm + 2x teleconverter capturing spectra with the 350D. Just working out the various lines/bands and instrument response thru VSpec at the moment. Appears to be approx 3 - 4 angs/pixel
Did all the major stars in Crux a couple of weeks back, which I plan to compile into a single image...Certainly looks different
Sounds like you're doing OK; you're getting spectra and analysing them, that's what it's all about. Like any type of observing it takes some practise to understand what you are looking at, what the instrument can see and what it all means.
You have quite a variety of Spectral classifications with Crux ( I remember that wonderful photo by Malin, stepped out of focus to show the colours!)
and that will allow you to "train" your eye in looking at the various features.
I find the responce curve of the standard Canon 350 dies in the UV and IR so it is very difficult to record info in these areas. Calibrating the curve helps a bit, but if there's no info there; there's no info there!!
You could also try the DSI mounted behind the lens, the responce curve I believe is much flatter.
Richard has taken an interesting SA100 spectra of the Planetary NGC 3242 which cleary shows the bright emmission lines ( see attached) This shows what can be done with pretty basic instrumentation, it can only get better!!
Going to bigger and more complex spectroscopes means more work in setting up, guiding etc etc etc, enjoy the simplicity while you can.
Ken,
exactly right. Christian Buil had a response curve of the 350D on his website. As expected, an un-modded 350D will cover 4000 - 7000A, and then dies rapidly. He showed that taking out the IR filter makes a big difference but at this time I want to keep the DSLR as is.
I have a Mogg adapter for the DSI + my M42 lenses, haven't tried them yet, but it sounds like a good project for the wekeend....
The responce curve also caused me some problems when trying to test various Energy Rejection Filters ( ERF) for solar scopes. I couldn't see far enough into the UV ( down below the CaK lines) and into the near IR to verify that the filters had good UV-IR rejection!
I'm currently using the Classical spectro to test PST etalons. These filters work by causing transmission/interference "bands" along the spectrum about 1A wide and 10A apart, obviously one of the "pass" wavelengths is the Ha, but they also pass a LOT of light all the way down to the UV. This is the job of the blocking filter; to suppress all these "bands" and only allow the Ha to go through.
Weather permitting, I'll get some images to show the results.
All this from an old binocular lens, a s/hand Zuiko 135mm telelens and a reflection 1200lpm grating!!!!
With some time out for family, a build of a 100mm Ha solar scope, I managed to get back to the Littrow project.
Well, almost there!!
The build other than some cosmetics is finished; the optics have been checked and tested on my reference source and the camera adaptors all tuned up!
It's only 200 x 200 x80mm and weighs 1225gms, that's almost 500gms lighter than the classical!!!!!
With Mike's agreement I'll finish the article on its construction and upload.
Hi Ken,
it looks good , far better than what I could generate
Would you be putting in a list of parts in the upcoming article?? Do you have any tips on the mounting for the reflection grating?? I'll be ordering a 1200l/mm from Edmunds, but the ability to turn it while maintaining the alignment of the front face is a bit tricky..
Mark,
I'd recommend the Optometrics 30 x30 grating, (cheaper than Enmunds!)this is usually 6mm thick.
The mounting I use is a piece of 25mm diameter aluminium bar 45mm overall length. The shaft is 8mm bright steel, so the mounting is drilled on centre 8mm.
To support the grating I've milled a "slot" 18.5mm deep ( 12.5 + 6) by 30mm long. This leaves a D shaped land about 18mm wide. Two 3mm tapped holes in the base lock the mount to the shaft, giving a centre height for the grating of 30mm ( hence the 60 x 60 box construction)
The grating is then mounted central to this land using a couple of strips of double sided tape.
The article will have some more detail on the mounting and enough info to build one!
If the demand was there ( minimum of 10) I could make up a kit of parts.....
Excuse me, are you guys talking about splitting a stars light spectrum here and getting images like merlins66s 4th post and 4th image? I'm new to this but very interested. I've been trying to make sense of Christian Buil french language pages on this.
Tandum,
Basically yes!
The idea is to use the spectroscope to break up the starlight into a spectrum and look at the various dark and bright areas. These "lines" can give us some valuable data on the type and consistancy of the star.
Many beginners use a StarAnalyser, Baader or Rainbow transmission grating ( it looks like a 1 1/4" filter) which gives a good low resolution spectrum. It can be mounted on front of a tele lens to give some good spectra or mounted infront of an eyepiece in your telescope to give a more detailed magnified image.
The next step is to use a fine slit at the focus of the telescope to improve the resolution to the grating.......
There's an article on file which might help. I've also uploaded a detailed write-up on the Littrow with some good references. We're here to help and encourage!! http://www.iceinspace.com.au/index.p...63,339,0,0,1,0
Just "tuning" the neon reference lamp in the Littrow.
Ideally I'd like to get the neon reference spectrum sitting just above the main spectrum to make comparison easier.
This shot is a single Canon 350 frame ( 1/10 sec, no computer enhancements/ additions) of the fluoro test bulb and the neon. You can see from the annotations the wavelengths of both.
In the ol' days the professionals used a Dekker screen at the slit to produce an spectral image of a reference light ( sometimes Iron) just above and below the object spectra; a microscope would then be used to measure the relative positions of the lines. This is not required nowadays as the lines can be measured using their pixel position on the CCD frame, but it looks nice!!.
Well the Littrow is almost there. Just "tuning" the slit and grating alignment and found that it's a bit more fiddly than the Classic. The alignment of the collimated beam reflected from the grating is critical. The spectrum also tends to be slanted across the field of view, so if it's not corrected a zero image may be exactly on the centre of the CCD but the red image could be moved outside the pixel area of the CCD.
My grating is inclined at about 2.2 degrees to the axis of the collimator and I found I needed to "rotate" the grating on the mount support clockwise by 0.52 degrees to reduce the movement on the CCD from Zero to Red to within 0.1mm.
Also changed the grating to the Optometrics 1200 lpm and get about 0.55 A/ pixel with the Canon 350D, FWHM of 0.9A giving a resolution of R= 6005.
I'm about to order a 2400lpm grating to increase this resolution to R = 12000, this will give enough resolution to see the fluctuations in the Ha emission lines in the EB stars ( Eclipsing Binary).
Need a small 12V DC to 240V AC convertor; about 5W capacity. That way I can safely use the Neon from a 12V battery. Anyone seen anything like this? I've got a circuit diagram if anyone can build it ($$) for me.
Hi Ken,
I read your article on the final spectroscope design with interest. A colleague has given me some optical fibre which I've been playing around with, and trying to get light through some diffraction film. The fibre works OK and I'll be making up one of the designs shown in the attached file.
They are fairly close copies of the designs Christian Buil has on his website, mainly his MERIS s/scope.You mentioned Optometrics as the preferred grating, would it be the model 3-3650? It's a 600 lpm, 500nm blaze, 30x30x9.5mm in size.
Any comments on the proposal are welcome, particularly the choice of the grating, 600 v 1200 lpm??
I would also look at making the 26mm eyepiece+fibre connection a single item. That way it could become a bit more portable between telescopes??
Mark,
have you seen Reiecke's design page? http://www.stsci.de/fg/pdf/reinecke.pdf
He uses an OAG body between the scope and the lens..... and an illuminated needle as a reference slit
That's the correct grating; I'd recommend starting with the 600lpm and then later ( or if you can afford it get both!) the 1200lpm ( # 3-3150)
This will give full spectra range coverage with the Canon.
I'm finding another issue I haven't seen noted elsewhere with the Littrow; I seem to be losing some contrast, which I think may be due to primary reflections from the surface of the collimator lens nearest the camera. It's a coated lens but with a pretty flat surface???!!
Mark,
You don't need to use an eyepiece at the front end. The fibre doesn't need a collimated beam entry and could handle say an f6 input cone; this would give about f3-f4 output.
There's some headaches getting the star image onto the fibre... Tom Kaye in his PAS article, p183 shows a solution using a hypo needle to hold the fibre and allow guiding on the "cut nose" of the needle; still pretty small but obviously doable.
Ken,
managed to get some time to work out what I was doing. I've placed the fibre in an old 1.1/4" webcam adapter in the eyepiece holder of the scope, the other end at the back of a 135mm slr lens to collimate the light. From there I can place the 350D, with the SA100 on the front of a 135mm lens, and focus on the end of the fibre. The lens are basically 1" apart. The setup looks very similar to the LORIS spectroscope on Christian Buils website, but the entrance slit has been replaced by the fibre.
Tests last night on a 12V red neon + a halogen desk lamp show approx 3 - 4 angstrom/pix.
I'll post some photo's of the setup when I can..
Now, to just get the grating.....
Mark,
Sounds like things are coming together. How did you mount and align the fibre in the adaptor?
5A/ pixel should easily show you the sodium pair!
My 2400 lpm grating is due early Sept. In the meantime I'm still doing focussing trials and have found the slit has to be rotated even more to give best resolution.
Weather permiting (???) I'll post some of the images.
Ken,
the adapter was from Steve Mogg, so it has a small diameter "tube" where it is meant to screw into a webcam. The fibre has a metal fitting that is slightly smaller than the tube, so I used some blue-tak () to centralise the fibre. I also have some 500 l/mm grating film from Edmunds Optics, which I was testing last night, and if my calcs are right, and they should be because I took the time to "calibrate" the system against known lamps and optical set-ups. The end result, using 2 x 135mm lens, some 500 l/mm film, an old slr camera body to hold the exit end of the fibre and I got a resolution of 0.9 ang / px on the std 350D dslr!!
I might hold off on the grating for a little while to play around with this setup a bit more.
The major downside is that the film is not blazed, so I'm losing 50% of the light as gets diffracted
To get that resolution with a 500lpm grating you are doing extremely well!!
What size fibre are you using?? I have a 50micron sample but had difficulty mounting it square and then being able to position a star on it! Now I use a 40mm length of it as an artificial star in my tester!!
) to centralise the fibre. I also have some 500 l/mm grating film from Edmunds Optics, which I was testing last night, and if my calcs are right, and they should be because I took the time to "calibrate" the system against known lamps and optical set-ups. The end result, using 2 x 135mm lens, some 500 l/mm film, an old slr camera body to hold the exit end of the fibre and I got a resolution of 0.9 ang / px on the std 350D dslr!!
