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2 minutes ago, Merlin66 said:

Louise,

Think of the reflective slit plate as an off axis guider... but where the pick off mirror is large and on the optical axis so it picks up a guider FOV as big as the mirror/ guider chip.

In the middle of this "pick off mirror" we have a very fine gap (the slit) say around 20 micron wide. We need to focus the target star into this slit gap and still be able to guide for as long as required. The starlight then goes through the slit and into the spectrograph....the light is collimated (made parallel) and reaches the grating which disperses the light into the spectrum.

This spectrum is then refocused (after the grating) by the imaging lens (or the collimator in the case of a Littrow) to present a spectral image to your imaging camera.

Hope this helps.

 

 

Yeah, I've figured all that out now :)

Louise

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Louise,

Although not the best solution the beamsplitter guider worked reasonably well.

We developed a "virtual" slit which could be registered to the actual as a means of acquiring and guiding on the target star.

A Vixen flip mirror body was used:

http://www.astronomicalspectroscopy.com/files/Vixen mod.pdf

Al's reticule was used...

AlsReticule33.zip

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Hi Louise,

Christian Buil has a nice page which goes through the design of a classical spectrograph here

http://www.astrosurf.com/buil/us/stage/calcul/design_us.htm

The Shelyak  instrument probably most similar in concept to the lowspec is the LISA, which is also a classical spectrograph design, though the better LISA optics give better performance at the UV/IR ends and allow it to be used on larger aperture faster telescopes. The lowspec is more versatile as you can change the grating to alter the resolution. 

The LHIRES is a Littrow design in which the light passes through the same lens on the way to and from the grating. This was originally an open source design by Christian Buil and others and was sold as a not for profit kit by the design team. (Mine is one of these) The Shelyak company was then set up to offer it commercially.  You can still find all the drawings etc here but it is not really practical to build one yourself as a one off, though some people have.  

http://www.astrosurf.com/thizy/lhires3/index-en.html

Cheers

Robin

Edited by robin_astro

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1 minute ago, robin_astro said:

Hi Louise,

Christian Buil has a nice page which goes through the design of a classical spectrograph here

http://www.astrosurf.com/buil/us/stage/calcul/design_us.htm

The Shelyak  instrument probably most similar in concept to the lowspec is the LISA, which is also a classical spectrograph design, though the better LISA optics allow it to be used on larger aperture faster telescopes. The lowspec is more versatile as you can change the grating to alter the resolution. 

The LHIRES is a Littrow design in which the light passes through the same lens on the way to and from the grating. This was originally an open source design by Christian Buil and others and was sold as a not for profit kit by the design team. (Mine is one of these) The Shelyak company was then set up to offer it commercially.  You can still find all the drawings etc here but it is not really practical to build one yourself as a one off, though some people have.  

http://www.astrosurf.com/thizy/lhires3/index-en.html

Cheers

Robin

Have seen all those, thanks!

Louise

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