BESOS: a prism spectrograph

10/23/12 <strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong> |<br />

BY CGUIRAO | APRIL 10, 2011 · 12:54 PM<br />

<strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong><br />

Introduction<br />

We present here our based <strong>prism</strong> low resolution <strong>spectrograph</strong> baptized <strong>BESOS</strong> or BEst Simple Optical Spectrograph<br />

(kisses in spanish). Designed in 2003, the <strong>spectrograph</strong> was proposed to overcome the low throughput of our previous<br />

instrument LOROS (coming soon to this blog) which was an instrument based on an on-axis dispersion <strong>prism</strong> obtained<br />

from a commercial spectroscope. The total efficiency of LOROS was only 25% in the visible spectral range. <strong>BESOS</strong> was<br />

built with only two doublets and a <strong>prism</strong>. This configuration reached almost 87 % at 620 nm. With such efficiency and<br />

low resolution, we expected to measure the red shift of the most bright galaxies and quasars.<br />

In this post we provide a description of the instrument, features, performances and the set of mechanical drawings.<br />

Optical design<br />

The Figure below shows the optical design of <strong>BESOS</strong>. The description of the elements is given in the Table below. The<br />

<strong>prism</strong> works at the minimum deviation and for this configuration the incidence and refracted angle to the input and<br />

output <strong>prism</strong> surface is 59.6960º respectively.<br />

Besos prescription data<br />

spectroscopy.wordpress.com/2011/04/10/besos-a-<strong>prism</strong>-<strong>spectrograph</strong>/<br />

Besos optical design<br />

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Two LINOS (now Qioptiq) doublets were chosen as collimator and objective respectively. An equilateral 60º <strong>prism</strong> from<br />

Edmund Optics was used as disperser. The image quality at 400, 550 and 700 nm is illustrated in the following Figure.<br />

The square is 20 μm side. The images for these 3 wavelengths were optimized to have their minimum spot<br />

size perpendicular to the dispersion.<br />

Technical data<br />

spectroscopy.wordpress.com/2011/04/10/besos-a-<strong>prism</strong>-<strong>spectrograph</strong>/<br />

Besos. Spot diagram<br />

Instrument Prism <strong>spectrograph</strong><br />

Name <strong>BESOS</strong> (BEst Simple Optical Spectrograph)<br />

Description Low resolution <strong>spectrograph</strong> based on an equilateral <strong>prism</strong><br />

Slit Ni plate Ø 10 mm, 25 µm thick, centered slit:25 µm width, 2 mm<br />

long. Labelcomat (B)<br />

Collimator Doublet f = 30 mm, Ø 12.5 mm, external mount. Ø 25 mm. Linos<br />

ref. G052008000. Glass: SF18. Coated: ARB2 VIS<br />

Prism Dispersion <strong>prism</strong>. Material SF18, 15x15mm. AR coating. Edmund<br />

Scientific Ref U43-494<br />

Objective Doublet f = 40 mm, Ø 12.5 mm, external mount. Ø 25 mm. Linos<br />

Telescope interface Standard 1.25” tube.<br />

Camera interfaces T2 thread<br />

ref. G052010000. Glass: SF18. Coated: ARB2 VIS<br />

Eye piece. f = 20 mm, standard barrel Ø 1.25”, with extender15 mm, Ø 1.25”<br />

Slit illumination Red LED, 10 mA.<br />

(included). For direct spectrum or slit observation<br />

Power supply Battery 12 V Model MN21/A23/K23A/LRV08<br />

Slit viewer lens Doublet f = 30 mm, Ø 12.5 mm, external mount Ø 25 mm. Linos<br />

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10/23/12 <strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong> |<br />

ref. 063130<br />

Slit viewer interface Internal tube standard Ø 1.25”<br />

Total transmission (without CCD) Efficiency (%) Wavelength (nm)<br />

spectroscopy.wordpress.com/2011/04/10/besos-a-<strong>prism</strong>-<strong>spectrograph</strong>/<br />

61.7 385<br />

83.8 437<br />

83.2 545<br />

86.7 621<br />

86.1 676<br />

CCD test camera SBIG ST-7 XMEI, KAF-0401E 756×510, 9×9µm<br />

Dispersion 0.72 nm/pixel @ 650nm<br />

Spectral range 362 nm – 812 nm<br />

Resolution λ/Δλ Wavelength (nm)<br />

Technical drawings<br />

— 594<br />

— 693<br />

— 720<br />

All <strong>BESOS</strong> technical drawing ara available for download in this PDF document: BesosAllDrawings<br />

<strong>BESOS</strong> Assembly<br />

This image describe the <strong>BESOS</strong> assembly with both optical and mechanical components. The only remark worth being<br />

mentioned is that the mechanical part 3 – Folding Mirror is made enterily of black anodized aluminium except the<br />

inclined surface that has been polished till it achieved the quality of a mirror surface (probably would habe been simpler<br />

solution to glue a small mirror).<br />

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10/23/12 <strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong> |<br />

Gallery<br />

The following photos show <strong>BESOS</strong> in different configurations<br />

spectroscopy.wordpress.com/2011/04/10/besos-a-<strong>prism</strong>-<strong>spectrograph</strong>/<br />

<strong>BESOS</strong><br />

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10/23/12 <strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong> |<br />

spectroscopy.wordpress.com/2011/04/10/besos-a-<strong>prism</strong>-<strong>spectrograph</strong>/<br />

SRL camera as detector and a webcam as slit viewer<br />

<strong>BESOS</strong> ready for observations with SBIG ST-8 and webcam<br />

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10/23/12 <strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong> |<br />

Observations<br />

spectroscopy.wordpress.com/2011/04/10/besos-a-<strong>prism</strong>-<strong>spectrograph</strong>/<br />

<strong>BESOS</strong> at the telescope with SBIG ST-1603ME<br />

Mallorca (Spain) .November 2003. All exposures between 1 and 120 seconds.<br />

“<strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong>” by CAOS group is licensed under a Creative Commons Attribution-Non-Commercial-No<br />

Derivative Works 3.0 Germany License.<br />

Based on a work at spectroscopy.wordpress.com.<br />

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2 Responses to <strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong><br />

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10/23/12 <strong>BESOS</strong>: a <strong>prism</strong> <strong>spectrograph</strong> |<br />

Frank Larsen<br />

June 27, 2011 at 12:33 pm<br />

Hi CAOS group<br />

Very Nice – just the information I needed for building a similar Faint Object Spectrograph, but using another type<br />

of <strong>prism</strong> I happen have in the drawer.<br />

Question:<br />

The guidehead – is the ST4 parts stock or specialmade?<br />

Keep posting please.<br />

cguirao<br />

June 27, 2011 at 2:41 pm<br />

Dear Frank,<br />

The guidehead of <strong>BESOS</strong> is specialmade, but simple to redesign to adapt it to your needs.<br />

<strong>BESOS</strong> was one of our first designs. In those day we were very fortunate to count with a mechanical workshop that<br />

could make us any part we wished. These days are gone.<br />

If I had to redesign <strong>BESOS</strong> again, I would replace the guiding port of the guidehead (that is, parts 4,5,6 and 7 in our<br />

Assembly drawing) with just single part with an internal 1.25″ tube. I would then fix a f/20mm lens to a webcam<br />

with an 1.25″ adapter. Also part 3 (folding mirror) could be replaced with a simpler part with just a small mirror<br />

glued to it and the whole screwed/glued to the head wall.<br />

Hope it helps Cheers Carlos PS. Stay tuned, there are new articles coming soon to our blog.<br />

spectroscopy.wordpress.com/2011/04/10/besos-a-<strong>prism</strong>-<strong>spectrograph</strong>/<br />

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