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robin_astro

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About robin_astro

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    http://www.threehillsobservatory.co.uk

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  1. Depending on what lines you are looking for you dont need to go that far into the IR. For example at high redshifts the Lyman jump in the UV at 1216A is shifted into the visible eg as here at z=3.87 http://www.threehillsobservatory.co.uk/astro/spectra_22.htm and at low redshifts the H Balmer lines are still measurable without an order filter eg as here http://www.threehillsobservatory.co.uk/astro/spectra_12.htm (bottom of the page) http://www.threehillsobservatory.co.uk/astro/spectra_21.htm Robin
  2. Alternatively you can use a wedge prism to separate the orders vertically (like an echelle spectrograph) This does have the disadvantage that the spectrum is slightly curved though Robin
  3. Hi Vlaiv There is no light in astronomical spectra below 3100A (The atmospheric ozone cut off) so you can go for a higher cut off than that if you like . I used a 610nm Baader filter which I happened to have which has the advantage that the Sodium light pollution is kept out of the IR spectrum. http://www.threehillsobservatory.co.uk/astro/Classifying_red_stars_using_a_Star_Analyser_VdS_poster.pdf In practise though you can typically measure up to ~7000A with the Star Analyser unfiltered as the signal in the second order is very low below ~3500A because of the low sensitivity of the camera and the high blaze efficiency of the grating Cheers Robin
  4. robin_astro

    `DIY` spectrometer first light!

    The M42 spectrum is impressively clean considering your light pollution. Did you subtract a sky background spectrum ? Cheers Robin
  5. robin_astro

    `DIY` spectrometer first light!

    Hi Tobias, Are you planning to use use a solar analogue to divide the lunar spectrum by to calculate the lunar reflectance spectrum and how are you correcting for atmospheric extinction? Cheers Robin
  6. As a practical introduction to one aspect by Carl Reade. (Milky Way Hydrogen line observations) I can suggest this thread. Initially with the helical but later in the thread much better with a small dish I think my dad put a soldering iron in my hand when I was born and helped me pass my RAE back in 1964 aged 14. Still hold a ticket (G8DVW) but not been active for many, many years
  7. robin_astro

    Starting out in Spectroscopy?

    In the UK the best price for the Star Analyser will likely be direct from the manufacturer https://www.patonhawksley.com/gratings Robin
  8. robin_astro

    Starting out in Spectroscopy?

    Hi Gav, The focal length of the Cooke will be too long to give decent resolution used with the small sensor ASI camera I think but might possibly work with the modded DSLR where you can spread the spectrum out further. (The maximum resolution of the spectrum is effectively defined by the size of the star image relative to the length of the spectrum, then there are some additional aberrations due to the simple converging beam arrangement which ultimately limit it) . You could try a focal reducer but I suspect this setup will show significant chromatism though in any case, losing focus at the blue/UV end, seen as a "fishtail" at the end of the spectrum. The 200mm f5 Newtonian though would be an excellent choice if you can set that up. (You could almost piggyback it and use it as a finder/guidescope for the Cooke. The mount might not notice the small extra weight ) I dont know the Chamelion 3 I'm afraid. A quick google suggests it comes with various sensors so you would need to plug the appropriate numbers into the calculator. Does it have any long exposure capability ie a few seconds at least ? If so, it could be a better choice than the ASI 120. Room for experiment there I suspect Cheers Robin
  9. robin_astro

    Starting out in Spectroscopy?

    Christian Buil has some nice images and tips for using the SA with a DSLR (The wedge prism it is not needed) http://astrosurf.com/buil/staranalyser/obs.htm It helps extend the wavelength range if the IR blocking filter has been removed as here, also for the ASI120MC if it can be removed. Robin
  10. robin_astro

    Starting out in Spectroscopy?

    Did somebody Call ? Hello Gav, Yes either camera can be used with the Star Analyser but I would suggest the ASI120 for starters. A mono camera if available would be better though for the various reasons I outline here https://groups.yahoo.com/neo/groups/RSpec_Real_Time_Spectroscopy/conversations/messages/6782 To use the SA100 with the ASI120, you just screw it onto the nosepiece and use it pushed into the eyepiece holder as you would for normal imaging. You might want to add a spacer or two. For best resolution check the calculator and keep increasing distance from the sensor until the calculator starts complaining. https://www.rspec-astro.com/calculator/ Exposure times depend on how faint the target is (Anything from less than a second for the brightest stars to tens of minutes for mag 12 quasars or supernovae) but there is no need to guide, just align and stack shorter exposures. (An SA100 spectrum is typically about 6 mag fainter than the equivalent star so if you can record a mag 16 star say in a normal image say, you should be able to record a spectrum of a mag 10 star) For example there are many examples on my website taken using a mono modified webcam which should give some idea of the performance with the ASI120. The 10 inch Cooke refractor is a spectacular instrument but may not be the best choice. (What is the focal length? The SA works best with shorter focla lengths provied the focal ratio is higher than ~f5) What other scopes do you have? I would say the sweet spot for the SA is something like an f6 6-8 inch newtonian or a 100mm f6-8 apochromat. At larger apertures/longer focal lengths you can go fainter but resolution suffers Note that the Star Analyser is a very low resolution device, typically around 30-50A resolution so will not show fine details but works best on objects showing bold spectroscopic features. Cheers Robin
  11. Yes the camera protective window/sensor cover glass response should be reasonably flat in the visible range (Though could affect the absolute value significantly if not AR coated, which some are not) The effect in the UV is more obvious eg Buil's measurements here http://www.spectro-aras.com/forum/viewtopic.php?f=45&t=2085&start=30
  12. The Here is the full description of the technique Buil used, from his website. Note his comment that the response of a complete camera may not be the same as the sensor because of the protective glass quantum efficiency of Sony ICX285 and ICX694 CCD devices is calculated from comparison with observed signal on a KAF-3200ME CCD camera (QSI-532) and a KAF-8300 CCD camera (QSI-583). The KAF-3200ME and KAF-8300 QE are assumed to be known and exact. The measurement is madewith a spectrograph LISA. The formula used for extract quantum efficiency is: Note: the computed effciency is the "apparent QE" for a given camera (camera glass windows and detector coverglass optical transmission impact the result).
  13. Have you asked Christian Buil ? Robin
  14. The masters thesis above also uses a similar technique but a monochromator is used in place of the spectrograph and a calibrated silicon diode in place of the reference camera. What sensor do you want to measure? Is there not a published QE curve for it? Robin
  15. Yes that is what Buil did. You need a camera with a known response to compare with though Buil's measurements were done independently of the manufacturer's published sensor figures and do not always agree. For example the cameras have a protective glass which also has a filtering effect
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