New HM spectroscope

[theodog]

Hi All,
I have nearly finished my model of the BAA spectroscope -1st image.
As a test I pointed it at an energy saving lightglobe, found the zero image and then moved the offset mirror to find some lines. I have no idea what they are, as I have yet to callibrate the instrument.

The image quality is poor and unfocused because it is the very first image. The camera was an old DSI.
However, it gives me enough encouragement to carry on.
Note the Diffraction grating should give adjustable dispersions and hopefully greater resolution.
:D

[sheeny]

Cool!

Keep us posted, jeff!

Al.

[Merlin66]

Looking good, a few minor "adjustments" and you'll be there!!
Try a small neon indicator bulb as a reference. It makes it easier to calibrate and confirm the resolution etc.
There's a fully annotated graph on Buil's page ( if you haven't already got one) or PM me - I have a copy!!

PS I've just re-editted Buil's SIMSPEC spectro design spreadsheet V2.2(now E1V3), in English; removed the "flux" stuff and corrected the resolution calculation to reflect the use of narrow slits. I'll upload if I can, if not drop me a PM for a copy.
Appreciate feedback

[Merlin66]

Jeff,
How are you getting on with the new spectroscope? Any results yet?
Calibrated?

[theodog]

Mmmm. Still having some niggly problems. Offset adjustment screw not smooth -I will use a thicker screw 3/8 rather than 1/4". This means I have to mill a thicker wall to take the thread without lateral movement.
Also, the image I obtained of the energysaver light globe was taken without an objective lens, I thought it was too faint to get stellar images, then I realised my mistake and hand held a 50mm objective lens infront of (and focused on) the slit:doh:. Much brighter result:D. Now working on a nose-piece.

So, no real results yet. Still looks promising 'though.

Ah, no. I am however, setting up the spectral lamps at work. We have a H, He and maybe a Ne. This should give a definate callibration. My guess is that it will take >3 frames of the DSI to cover the light region.:eyepop:
Progress has been slow, but I have been keeping up with progress on this forum. Great info.:thumbsup:

[Merlin66]

This spectroscope design first appeared in a paper by C.J. Watkis, published in the Journal of the BAA, and appears on page 280 of no.4 (the June 1976 issue) of Vol. 86.
Credit where credit's due!! Thank you Mr Watkis.

[theodog]

Credit where credit's due!! I Agree.
I have no books on Spectroscopy directly, amature or professional, so I have been relying on the info presented in this forum.
I do have some books that contain basic info on stellar spectroscopy and a general knowledge sufficient to teach secondary students.
The work of C.J.Watkis, albeit gained by second hand, has been inspirational.

Having said that, here is my beefed-up mirror rotator screw. It works much better that the 1/4" thread before.
Now working on the 2" nosepiece.
:D

[Merlin66]

Jeff,
C.J.Watkis was the BAA Instrument Section Director at the time. I just felt uncomfortable offering up up the design from memory....
Remind me... why did you upgrade the adjusting bolt?
On both my spectroscopes the small balance spring just holds the grating ( similar to your mirror) against it's own weight and there's very little resistance to rotating the grating. I'm thinking of the possible difficulties in getting repeatable settings.... maybe the holding screw needs to be replaced with a small sleeved bearing....

[theodog]

Merlin66,
I replaced the adj. screw because the 1/4" threaded through a 3mm wall provided too much lateral movement. So I milled down a 1" thick block so that it could take a 10mm bolt and add lateral support. The spring is fairly stiff.

I would love to have a reflection grating to move instead of the mirror, maybe one day. I am investigating the use of an educational grating set, 100, 300 and 600 l/mm; allowing more flexability in resolution.

There may be some of the movement you describe as the rotating mirror bearing surface wears, I'm assumeing that it wouldn't be rotated all that often. Yet another problem that may develop and require a solution. Keeps the mind busy.

[Merlin66]

Ok!!
I had similar problems with an earlier build and got around it by using one of those 1/4" threaded inserts ( the type you hammer into wood to give a thread) filed of the tangs and then expoxied it into a 8mm hole in the sheet metal... Gives about 8mm of thread and support to the screw... maybe a bit late advice for you... but may help others.:rolleyes:
You'll probably find, depending on the grating, that you have to use it everytime! To go from zero image to the spectrum! Maybe a disk of milk bottle plastic would help??

[theodog]

Now this took me by suprise.:eyepop:
Taken through my project with a DSI of an energy saver lightglobe. No objective lens -naked slit. 100l/mm grating.
Mosaic(2) of each 20x 0.5sec colour exp in jpeg. Zero image about 2 frames to right.
Something seems to be working.:party:
:D

[Merlin66]

Jeff,
well done! Your first spectrum with the set up- very satisfying I'm sure!!
( BTW spectra ALWAYS should be displayed blue to the LHS and Red to the RHS!:thumbsup:)

[theodog]

Yep. Wrong way around -sorry.
Here I have compared with a previous image taken with a paper (CD) spectroscope and posted in the Spectroscopy thread.
I rotated it for convention.
At least the newy has better resolution.
:D

[Merlin66]

As you say much better resolution...
Check your focus, I think you could do better!
If you can find an OSRAM Duluxstar energy saving bulb, it would make a good reference spectrum; the emission lines have been pretty well documented.
The attached images might help in getting were you want to be!!

[theodog]

OK, Looking for an OSRAM globe.
Meantime I have completed the nosepiece.
It is 2" outside diameter for focusers and an internal thread that will take a 1 1/4" nosepiece adapter. Also with some plumbing tape a Pentax screw thread for lenses.
Just the simple sides to do.
:D

[Merlin66]

I think I got my Osram flouro's from an IGA store in Melbourne.
It's coming together!
Your should make up a dial scale for the adjusting screw; then you can zero it @ zero image and calibrate by central wavelength - making it much easier to use in the dark on the scope. Adding a small back light red LED to the slit makes it visible and easier to position a star.
Just my 2c as usual!!

[theodog]

No suitable OSRAMs in Coona. Many others eg Phillips.
We had 2 IGAs but they are Woolies and Coles now.
Coles had them but none in the standard bayonet fitting. Only screw and small bayonet.
I might go hunting for a suitable Mercury street light. Possibly also rare in Coona.
I'm off to the dedication of the new SkyMapper at SSO tomorrow.

[theodog]

Hi All,
I have finally managed to attach a lens & rebuild the slit using razor blades, no idea of the slit width -judges by eye to be small.
I also managed to crack the grating.:sadeyes:
It was a 200mm camera lens.
I learned that I can't attain focus with the ST7, so have to use the DSI.
This image is comp of 40x1sec exp mosaiced with another of the same.
Then croped for the best section of spectra.
Small steps.
:D

[Merlin66]

Jeff,
I ran your flouro spectrum though VSpec and got FWHM of 7 pixel, a dispersion of 2.8655 A/ pixel giving a resolution of 20A, equivalent to R=220... a good start!!
I think the slit width needs to be reduced: looking at a VERY bright light a 20micron slit looks like very very thin line of light between the blades...

[theodog]

Thanks Ken.:)
Could the slit width problem also be that the slit is out of focus(in the colimating lens), slightly?
I have tried to focus the camera better but can't get the lines any narrower. Also I just relied on a projected solar image to find the F.L. of the colimating lens, here I may be out by several mm's.
Next move is to remove the slit and lens and try exact measures on a table.
Also I have to work on a flip mirror system for aligning the slit on starlight.
:D

[Merlin66]

Jeff,
You're close enough with the focus that you could remove the grating and use the "camera" lens with a 6mm ( or so!) eyepiece to look back through the optical train and move the "collimating" lens ( or the slit - which ever is the easier!) to get the slit 100% in-focus.
Another thing to check is that the slit is parallel to the lines on the grating..
After that it's just practise, practise, practise....
I've tried MANY different methods of getting the star image on the slit and then being able to guide... the one that seems to work the best for me is a "clone" 50/50 beamsplitter. It allows me to find, centre and then guide on a star/ nebula etc etc. Cost about $80...

[theodog]

OK, today I spent time with my Physics class looking at spectra. Gave me an excuse to play with the spectroscope. We set up a neon tube in a light proof cardboard tube, placed a 200mm lens on the spectroscope and obtained the following image.
Data reduction through Vspec.
:D

[Merlin66]

Your off and running!!!!
BTW if you use this gear at school for teaching; can you write-off the costs against tax!!

[sheeny]

That looks pretty darn good to me Jeff!:thumbsup:

Al.

[Merlin66]

Jeff,
With the weather being what it is, I got to thinking!!
If, sometime in the future, you want to "upgrade" the Watkis to use a reflection grating ( 600 to 1200lpm), I think all you'd have to do is remove the transmissin grating and replace the adjustable mirror with a grating.....
If the size of your "camera" lens is OK you should get some excellent results! Two spectroscopes for the price of one (almost!).
What do you think????

[theodog]

Thanks Ken,
I have been thinking the same thing but will use the reflection grating in my next model.
At the moment I'm on the lookout for;
Cheap 2nd hand x by 40mm binoc's
300l/mm refl grating (probably from England P-H) and
adjustable slit (surplus shed seems to be out of stock).

Current model is for experimentation. I have changed the slit holder to include a smaller hole, and am looking at another to hold optical fibres -one for the star, another for a neon reference globe.
:D

[Merlin66]

In my opinion the reflection gratings from Optometrics are the best, and most cost effective.
I picked up a 30mm x 30mm 600lpm for us$125 recently, much cheaper than Edmund Scientific. Never see a P-H reflection grating mentioned on the other forums???
Andre/ Fred at Surplus Shed I'm sure will have the slits back in stock soon; they KNOW we use them all the time!
K-mart usually have pretty cheap binos.....

[theodog]

Ok. I will look at other suppliers.