Welcome to the spectroscopy board

[Merlin66]

This section of the Lounge is focused on supporting and developing amateurs getting started in spectroscopy.

This area of amateur astronomy has long been overlooked but is recently gaining more and more popularity as introductory gratings become available.

(can we make this a sticky above the board???)

 

[Dave In Vermont]

I've been using a diffraction-grating for analyzing stars for many years - whenever the spirit beckons. These are fun and not that expensive. In fact I was using mine last night. Here's the US source:

http://www.starspectroscope.com/

There's a nearly identical outfit in the UK, but the name escapes me at the moment. Google: Diffration-Grating spectroscope might turn the trick.

Dave

[ejp1684]

http://www.patonhawksley.co.uk in the UK.

Eric.

[ejp1684]

I've just finished building a classical spectroscope. Unfortunately the weather here in the UK is abysmal and I haven't been able to do any stargazing for weeks on end. I included a neon bulb in the spectroscope for calibrating, and that's all I've been able to test.

It's hammering down with rain at the moment and the outlook is grim for at least the next week, so not much chance of trying my new toy out for a while yet.

Eric.

[Merlin66]

Eric,

looking good!

what about posting a photo of the instrument.....

How do you intend to guide???

[Merlin66]

Dave,

Rainbow Optics no longer ship outside the US?

 

[Dave In Vermont]

I just noted that myself. ejp1684 saves the day with the link to http://www.patonhawksley.co.uk/aboutus.html

Have fun,

Dave

[ejp1684]

I’ve gone the DIY route because I can’t afford the ones for sale at £1000 plus. I chose the classical design because it seemed the simplest. If it works ok then I might consider constructing a different design.

I explored a few ideas on various websites, including one made with a 3D printer, but that was a complete 3D printed box to hold all the components. I’ve used a Prusa 3D printer to make an electronic focuser for my 8” SCT, so decided to make use of the 3d printer in the construction. This was my idea:

1. Use 10mm plywood for the base and the two sections which support the eyepiece connector and the camera connector. These two sections to be attached using an ’L’ section to ensure they are at right angles to the base. The component supports could then be screwed to the base.

2. Use 5mm ply for the sides and top, screwed and glued. This should provide a firm and strong box.

3. Use the 3D printer to make supports for all the components. Using PLA the supports would be light, strong, and accurate. By accurate I mean the vertical planes would be exactly at right angles to the base, and once I had made the support for the largest component - the camera lens - it would then be straightforward to make sure the centres of all the other components would be the correct distance from the base.

4. Using plywood and 3D printed parts would keep the weight to a minimum.

I used Ken’s ‘Astronomical Spectroscopy for Amateurs’ constantly. One feature mentioned there is to get a good laser light source for collimation. I tried a simple laser pen from eBay but it was impossible to get the beam centred. So I found a Laser Bore Sighter on eBay for about £8 which turned out to be perfect.

Because I needed to keep cost to a minimum I bought nearly all the components from eBay. One exception was the slit from Surplus Shed: they had run out and Ken kindly sold me one from his secret hoard. The dry run convinced me that a method of focusing the camera was vital. The best solution for this turned out to be the Baader T thread Helical Focusing Eyepiece holder. Unfortunately this was about £38, the most expensive component I had to buy!

To keep weight and cost down I found an achromat doublet on eBay and used that for the collimator instead of a zoom lens as mentioned in Christian Buil’s descriptions. It’s a 90mm focal length, f3. I used the SymSpec spreadsheet to work out the distances etc.

Photo 'of dry run'

Here you can see the ‘dry run’. The angle between the lines was 38º, and because the centres of all the components were already the correct height from the base, all I had to do was align the supports centrally and at right angles to the lines.

I used a mirror initially to check everything was lined up correctly.

Here's the assembled unit with details of the major costs components. Obviously there were other costs involved such as the wood (two small sheets from a local hardware shop for about £7 each) and other odds and ends.

I used 'L' sections of aluminium to make sure the eyepiece and camera connectors were at right angles to the base, and you can just see one of them below the camera connector. On the right side is the 12v socket for the led's and the two little switches above it are for the two led's to illuminate the micrometer and the slit scale. The Baader focuser is held in position with a 3D printed flange.

The central socket is for 240v power for the neon lamp. This is provided by an inverter from eBay for about £8. The two black lumps contain the red leds which illuminate the micrometer scale and the slit scale. The slit dial is just a 3D printed dial which push fits onto the dial of the slit mechanism, and this is protected by the cover.

When I first played around with the grating support using a simple bearing, there was too much play in it. When the micrometer screw was reversed the image in the camera would jump half way down the screen. So I used a Needle Roller Bearing as it's much taller and has less play. It took a while to file down the 3D printed insert so it would rotate freely but not move from side to side, but I got there in the end.

Using 3D printed parts meant I could design the component supports to get the collimator as close to the camera lens as possible without interfering with the light.

This shows the 10mm prism supported just in front of the slit mechanism. The neon bulb is inserted in the base of the support. On the left is the support for a red led which shines onto the front face of the slit.

 

The collimator stopped down.

My decision to use plywood and 3D printed parts seems to have been successful. The total weight of the spectroscope is 850gms, that's just 20gms more than my ES 34mm 'hand grenade' eyepiece!

Eric.

[ejp1684]

As regards guiding, my current scope is an Evolution 8. I bought this because I can't stand for long periods, especially when trying to keep my eye in the optimum position from an eyepiece. With the tripod in its lowest position I can sit for hours observing without any discomfort.

However, now that I have become interested in spectroscopy and made this thing, I plan to buy a second hand HEQ5 mount and convert it to belt drives if that hasn't already been done. Then I'll learn how to operate that, polar alignment, guiding, etc.

I've adapted a flip mirror, and replaced the mirror with a glass slide (thanks Ken!) So that's one option for guiding. The other is to use a separate guide scope, which I could also use for polar alignment with Sharpcap.

The next step (whenever this dratted UK weather cooperates) is to use the spectroscope with the Evo and iron out any quirks. It's one thing to design and build it in good lighting with my glasses on, but I guess quite another to use it in the dark. And I'll have to use it initially with the slit open, but it should at least be possible to make sure everything functions as it should.

I'd appreciate any advice others can give at this stage.

Eric.

[ejp1684]

Here are a few shots of the support components from Sketchup

 

The flange holding the Baader focuser in position.

Grating support which inserts into the needle bearing.

Support for needle bearing.

Canon lens support

Cover for slit dial.

Collimator support, base.

Collimator support, top.

Micrometer support.

Push fit slit dial.

Slit support (a cover screws onto the top to hold it in place). The prism sits between the two uprights, and the neon lamp is inserted into the space below.

Plate to hold the glass slide to replace the flip mirror.

Eric.

 

[robin_astro]

Hi Eric,

The spectrograph looks good but dont underestimate the acqusition, focusing and guiding issues with slit spectrographs.  Except for bright targets (where you can defocus)  you will soon want to incorporate a mirror slit guider.  Though not cheap,  mirrors slits which can be used in self build guider designs are now commercially available, eg from Shelyak

http://www.shelyak.com/produit.php?id_produit=122&id_rubrique=16

or Ovio

http://www.ovio-optics.com/jetons-de-diffraction-interferences,fr,3,56.cfm

for example.

Cheers

Robin

[robin_astro]

Hi Eric,

I have just  noticed your neon test graph shows the slit width as 5um. That is very tight. Is that correct?  with your 8 inch f10 scope the star image FWHM will be around 30um FWHM with typical 3 arcsec seeing so you will need a slit of around 25-30um to get reasonable throughput. What camera are you planning to use? Because you have a 5/9 reduction in image scale through the spectrograph you will need to watch out for potential under sampling. For a 25um slit for example the  pixel size will need to be < (25*5/9)/2  ie < 7um  

Cheers

Robin

[ejp1684]

Thanks Robin, error on my part, should read 15um. The camera I have at present is a GPCAM (mono) pixel size is 3.75. I plan to use my 6.3 reducer with the spectroscope.

Eric.

[tooth_dr]

I just ordered a Star Analyser 100 after an astro meeting last night on spectroscopy for beginners.

I have a choice of cameras and scopes, any advice would be welcomed. 

[Dave In Vermont]

I don't know if you already have this, but here's a short article on the Paton Hawksley Star Analyser 100 (SA100) to help you get started. I have the US version over here, and these things are great! Here's that:

The Star Analyser SA.pdf

And for an excellent and lucid book you might like:

"Grating Spectroscopes and How to Use Them" - by Ken M. Harrison. Springer. A Patrick Moore's Practical Astronomy Series book.

Enjoy! I'll look foreward to your 'First (Many-Coloured) Light' -

Dave

[Owmuchonomy]

+ 1 for Ken's book.

[tooth_dr]

Thanks @Dave In Vermont and @Owmuchonomy I was instantly fasincated last night at the meeting, I knew I wanted to give it a whirl.

 

Cheers, will have a look through all the info posted above.

[robin_astro]

Hi,

I am the chap who developed the Star Analyser back in 2004.  Looking at your list of equipment I would start with  one of your small refractors,  (the one with the lowest chromatic aberration) and the mono camera with largest sensor size. This will give the sharpest spectra and will be the easiest to process the spectra. A good reference for this sort of setup is Jim Ferreira's website.

http://www.lafterhall.com/spectroscopy.html

(Look for the results using the Star Analyser with an 80mm APO and a DMK41)

Cheers

Robin

www.threehillsobservatory.co.uk

edit: added link

[robin_astro]

Once you have mastered using it with the small refractor, then the 300mm f5 Newtonian will allow you to go deeper using longer exposures, provided your skies are reasonably dark.

You can find the official manuals for the Star Analyser on the manufacturer's website here

http://www.patonhawksley.co.uk/resources.html

and an on line  calculator to optimise your setup

http://www.patonhawksley.co.uk/calculator/

There are quite a few Star Analyser users on here so any other questions, just ask away :-)

Cheers

Robin

[tooth_dr]

@robin_astro Thank-you Robin.  The guy at our meeting was really praising the Star Analyser 100, and was basically blown away when his very first shot with it, using a 200mm lens and DSLR, yielded the spectrum of Vega!  The grating should arrive in the post tomorrow hopefully!

[Merlin66]

Robin has provided some good links for you....

I'd also add our webpage as a starting point..

http://www.astronomicalspectroscopy.com/How_to.html

Any questions/ concerns I'm sure we can answer.

 

 

[tooth_dr]

35 minutes ago, Merlin66 said:

Robin has provided some good links for you....

I'd also add our webpage as a starting point..

http://www.astronomicalspectroscopy.com/How_to.html

Any questions/ concerns I'm sure we can answer.

 

 

Thank-you also.  I will get this all read and give it a go, then come back to you all with, no doubt, some daft questions.