Elliott Instruments CCDSPEC spectrograph

[nytecam]

In case I've missed it but anyone got or used this £1300 astro spectrograph from Elliott? CCD cam extra.

Saw a review in current Astronomy Now and guessed from pic of straight tube and curved spectra that a prism was involved. From Googled diagram looks like a grism [prism+ grating] eg transmission grating on rear of prism for straight-through train and slit viewing scope ! Resolution = 1.5nm (400-700nm) Any thoughts?

[jsandse]

Always glad to see more spectroscopes on the market.

Haven't tried one myself so can't comment on quality etc

But I am sure it would be fun to try out :0)

cheers

John

[robin_astro]

Hi Maurice,

It looks like a close copy of the TRAGOS spectrograph http://www.burwitz-a...agos/index.html

designed by the CAOS "amateur" group http://spectroscopy.wordpress.com/ ( Elliott instruments appear to have applied for a patent but I cant see anything obviously new in the design) The TRAGOS was developed into a production prototype some years ago by Baader.They eventually abandoned it (not sure why) in favour of the DADOS reflective grating design from the same group.

Cheers

Robin

[nytecam]

Hi Maurice, It looks like a close copy of the TRAGOS spectrograph http://www.burwitz-a...agos/index.html

designed by the CAOS "amateur" group http://spectroscopy.wordpress.com/ ( Elliott instruments appear to have applied for a patent but I cant see anything obviously new in the design) The TRAGOS was developed into a production prototype some years ago by Baader.They eventually abandoned it (not sure why) in favour of the DADOS reflective grating design from the same group. Cheers Robin

Thanks Robin for the techno on the TRAGOS spectrograph - nicely detailed instrument. The 80mm fl collimator and 60mm fl camera lens would project the 25um wide slit to ~19um onto the sensor. As you say not much original and patentable about the Elliott spectrograph but expect all designers think their baby is unique ;-)

best regards MG

[the rev]

Hi Robin/ntecam,

How does this compare with the Lhires and Lisa?

Kate

[robin_astro]

Hi Robin/ntecam,

How does this compare with the Lhires and Lisa?

Kate

Hi Kate,

It is a low resolution spectrograph (15A, about 3x that of the Star Analyser) giving the full spectrum in one shot so the LISA and the DADOS are the best comparisons. It would certainly be interesting to put them through their paces side by side.

I have not seen the Elliott instruments spectrograph let alone used one but I can give some suggestions on what I would be looking for based on the design.

All three have similar reflective slit guiding systems which is an excellent way of solving the key issues of finding, positioning and guiding the star on the slit.

One of the difficult things to achieve with a spectrograph covering the full range in one go is to get the spectrum in focus across the full wavelength range, particularly into the blue. This needs quite expensive lenses so I would look carefully for the degree of deterioration in resolution at the extreme ends of the range.

At f10 it is similar to the DADOS. This relaxes the optical requirements compared to the faster LISA. The downside is you need a wider slit to fit the star image, reducing resolution. This then also limits the size of telescope which can practically be used (The LISA happily works with telescopes up to 0.5m. The other two are better matched to half this aperture).

It looks like this instrument has a relatively fine (for the resolution) 500/600 l/mm grating transmission grating and relatively short focal length lenses to keep it compact. The problem is, transmission gratings at this line density tend to be significantly less efficient than the equivalent reflection grating so I would be looking closely at the efficiency compared to the alternatives which use reflection gratings.

The 50um fixed slit seems rather wide to me even for an f10 instrument. The result is the rather modest 15A resolution. I happily used a slit half that width with my LHIRES and an 8 inch f10 scope. I would say a 30mm slit say would have been better for the typical small scope user and would have given a more useful ~10A resolution.

That is probably about as far as I should take it without actually seeing or using one ;-)

Cheers

Robin

[the rev]

Thank you Robin, just trying to sort out differences, so I know which one I want to save up for