The Latest LowSpec morph… V6.

Forums Spectroscopy The Latest LowSpec morph… V6.

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    Tony Rodda

    An OVIO slit and 1800 grating tuned to Ha with a modified front-end guider module containing fully adjustable guide mirror and guide lens combinations.  I used the 30um slit for testing.

    These pics are from the bench.  Just need a clear night to try out.

    The lamp calibration was using a home built calibration unit and a Neon lamp option placed simply at the ‘scope end.

    The optics used are low end.  I’ll mount better quality if/when proven.  The grating is “used”.

    There’s a few stray ‘hairs’ from printing and it needs cleaning.

    I used a small OrionG3 as a test camera.  8.6um x 752.  The Atik460 will provide higher resolution and should perform much better.

    But, for the Orion, the BASS calibration figs aren’t too bad:

    Point# Pixel Wavelength (nm) Error (nm)
    1 89.19 638.299 0.001220703
    2 123.64 640.225 -0.001831055
    3 310.45 650.653 0.002990723
    4 357.95 653.288 -0.002746582
    5 477.03 659.895 0.000366211

    Forrest Sims

    Absolutely Brilliant Tony!  What does the Vernier control at the top of your image of the spectrograph adjust?  Is this how you tuned the instrument to Halpha?



    Robin Leadbeater

    A nice looking instrument Tony.

    I like the idea of a high(ish) resolution version. Like the LHIRES, the chromatic aberrations should be less of an issue.  The foot of the lamp lines look rather broad though. Do you think this is down to the quality of the optics?  (I think I remember seeing something similar with a batch LHIRES which had poor quality  doublet  lenses, seen as an “elephant’s foot” shaped lines) . What focal ratio are you running ?

    Did you see the results Terry Bohlsen recently posted from his version at similar resolution (presumably also with an 1800 l/mm grating) on ARAS ?



    Tony Rodda

    Sorry for being off-grid recently – a very unpleasant cold after returning to the UK!

    Yes, the vernier adjusts the grating as standard.  I’d just placed everything so as to zero in on Ha. I can effectively ‘lock-off’ the adjustments to stay Ha orientated.  That’s what I crudely mean by Ha ‘tuned’.

    I’ve just refitted both the ‘printed’ scpectroscopes ready for observing – just need a break in this terrible weather!  Oh, for Arizona skies!

    PS, I got Wayne’s latest treatise and will respond asap.

    Regards T

    Tony Rodda

    Yes, you’re right, the chromatic aberation seems less of an issue with this ‘restricted’ mode of operation.  In fact the focus and calibration fit is incredibly good (even for a simple linear fit).  Still needs proving ‘at the scope’ though.

    That’s great stuff by Terry.  The range and resolution looks like a similar config. That gives great hope. Simspec suggests R~ 8000 for an 1800 + H9.  See below.

    I’m still using ‘not quite the best’ optics but I exacerbated the ‘elephants foot’ problem because I did something really dumb during the design stage…

    When I rescaled the camera lens to fit a larger item (same focal length) I unintentionally scaled the base/holder too.  This raised the lens off the optical axis.  Dopey or what? 

    I recognised the mistake when I stripped, cleaned and rebuilt the spectroscope ready for ‘final’ testing at the ‘scope.  I think I’d been so focused on keeping all the components orthogonal that I’d simply missed it.

    Anyway, new holders fitted.  That, and more careful placement of the calibration lamp (!), have produced much better results.

    Attached below are pictures from both the ‘re-adjusted’ spectros but using a SXH9 camera (1392 pixels) instead of the little Orion.  You can still see a small amount of line definition loss but this can be helped with careful lamp placement.  Still, I think that’s as far as these optics/configs can be pushed.  

    Anyway, very peasing results (albeit need to be proved in real life!) but enough success to warrant fitting better optics and a full resolution print.  I’d produced some decent test spectra on the few occassions I was able to mount the devices at the scope but there was nothing I’d want to submit.  That is, nothing that matched the accepted standard.  This gives me hope.

    1800 l/mm 30um slit ‘tuned’ to Ha…

    Spectro number 1, 600l/mm – 40um slit at 600nm to 750nm…

    A ‘refined’ guide image using a 40um slit (which might be to wide a FoV)…  I’m still experimenting with different lenses to find the best options – but that won’t happen until I get to use them in anger.

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