1- Introduction

UVEX is a spectrograph mainly intended for astronomical observations on relatively small sized telescopes (see detailed specifications below). Its special property is that you can manufacture it yourself, thanks to the 3D printing technology, although if you choose to build it yourself then you must also mount and adjust from scratch. The UVEX project in its current form is therefore intended for DIYers, those who want to understand the inner workings of an optical instrument, and teachers who want to offer their students a very rich, complete and motivating educational project.  Constructing and using UVEX is relevant to a number of subjects as you shift from planning to use, with the help of various physical phenomena (potentially supporting courses in physics, biology, chemistry…) and even astrophysical phenomena if the instrument is put at the end of a telescope!

You should be aware of the (moderate) risk of not reaching the end of such an adventure. And if your aspiration is rather to have a perfectly finished instrument that is immediately operational, it is better to turn to the wide ranging and high quality commercial offerings now available.

The project is presented here royalty-free for non-commercial use. Our goal is that you can complete the instrument, so here we provide information you will need for that purpose.

UVEX is a serious instrument, with which it is possible to carry out works of real scientific value. It is based on a simple configuration (essentially consisting of two mirrors) which gives it a good optical luminosity and a very wide spectral coverage, ranging from ultraviolet to infrared (depending on the camera used).  UVEX allows you to realize spectra of the visible part of the electromagnetic spectrum, but it is also worth emphasising its high efficiency in the ultraviolet, a domain almost unexplored by amateur astronomers today, and which will also interest professionals researchers. It is this feature that gives the name of UVEX, the acronym for UltraViolet EXplorer.

Here is the characteristic look of a star spectrum obtained with UVEX in the so-called “basic” configuration of the instrument (300 lines/mm grating, which is interchangeable):

This is the spectrum of the bright star Deneb obtained by mounting UVEX at the focus of a Celestron 8 telescope. Below is a detail of the violet and blue part of this spectrum showing that the detail is preserved in this area, a unusual feature in an amateur spectrographs:

But the ability to explore the infrared part of the spectrum is not forgotten, as evidenced by the two spectra of stars presented below (UVEX becomes an IREX!):

In a nutshell, UVEX is a low to medium resolution spectrograph. The resolving power R can range from R = 500 to 3500 depending on the slit width employed and the selected grating (from 300 lines/mm to 1800 lines/mm, the latter only usable for the blue part of the spectrum). As noted, both the input slit (typical width between 14 and 35 microns) and the grating are interchangeable.

UVEX is designed for use on relatively small and relatively slow telescopes. The typical instrument is a Schmidt-Cassegrain, Maksutov or Ritchey-Christian telescope of 150 to 280 mm in diameter with an aperture ratio of between F / 8 and F / 10. This is an important remark and a limitation that you must absolutely consider. If your telescope is open at F/5 (a Newton for example), UVEX is not really adapted: you will obtain a spectrum but it will be degraded (loss of resolution of 30% compared to F/10 input beam for a 25 microns slit and exploitable spectral domain reduced). An aperture at F/6 is in practice the brightest configuration usable with UVEX. Similarly, the use of a large diameter (500 mm and more) will require the use of a wide slit that automatically degrades spectral resolution performance.

The table below shows the resolving power (R) achieved at 650 nm for a telescope at F/10 and for various technical combinations offered by UVEX:

Opposite, the appearance of the solar ultraviolet spectrum according to the adopted configuration. UVEX is here mounted at the focus of a 10-inch F/8 Ritchey-Chrétien telescope that is pointed to a blue daytime sky.

UVEX has a removable camera interface. The currently designed interfaces are for ATIK cameras (see the photograph opposite) and ZWO cameras (the cooled models). For example, this spectrograph is very comfortable with a CCD camera ATIK 414EX or ATIK 460EX, or in CMOS with a camera ASI183MM pro.

The linear dimension of the spectrum usable in the plane of the detector is of the order of 13mm with a grating of 300 lines/mm and a telescope at f/10 (this would mean taking a spectral range of a little more than 4000 angstroms at one time with ASI183MM camera, for example).

The linear dimension of the spectrum usable in the plane of the detector is of the order of 13mm with a grating of 300 lines/mm and a telescope at f/10 (this would mean taking a spectral range of a little more than 4000 angstroms at one time with ASI183MM camera, for example).

A pointing/guidance device in front of the spectrograph is essential for astronomical spectrography. UVEX is compatible with the guiding cube designed for the Alpy 600 spectrograph from Shelyak Instruments. A 3D printed version of this device is also being designed in the context of the UVEX project.

For the most up-to-date information on the UVEX project, it is highly recommended to register on the ARAS forum, and to consult the section especially dedicated to the project (in addition to all the other exciting topics described in this forum, which are all invitations to observe with a spectrograph, whatever it is). We suggest you make your comments and questions on this forum.

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