4- The assembly

The first operation is to glue the slit ring UV03 in the space provided in the UV01 housing. It is necessary to use the correct orientation, aligning the markings drawn on the front of the pieces (it is inside this ring that the slit-holder proper will be mounted, which must be correctly oriented relative to the grating grooves):

The camera interface is then mounted (in the photos below, the ZWO camera model is shown). We use a set of M4 screws and nuts for fixing:

It recommended to then mount the telescope interface, which limits the risk of later contaminating the optical components through further handling after they are installed. The interface block used here is the Alpy 600 spectrograph guide block, which can be purchased from Shelyak Instruments. This high-quality piece of metal, which is essential for good observations, is however the most expensive part of the UVEX project. A study is under way to develop as an alternative a compact module for this function, which can be produced by 3D printing and which also includes the calibration elements (spectral calibration, white lamp) and the necessary electronics. Four M4 screws are used to mount the guide box:

The slit is mounted on its support UV04 (M3 screw). The following views show the use of a Shelyak slit (in this case the model that is screen printed in a chromium layer deposited on one side of a thin glass slide): : 

A clearance of approximately 1.0 mm must be left between the contact surfaces of the UV03 and UV04 parts (this distance may be adjusted when the instrument is tuned – see next section). Note again that an adjustment in rotation makes it possible to orient the long axis of the slit parallel to the grooves of the grating. The UV05 clamp is used to complete the fixing of the slit holder.


One option is to use a “clear” slit, also part of the Alpy kit that can be provided by Shelyak Instruments. It is actually a set of slits machined into a sheet of nickel 50 microns thick. They give you a choice of slit width and a 25 microns hole, which can be a very useful artificial star during bench testing. This slits system is more economical than the model on glass and more transparent, especially in the ultraviolet, but it is also more fragile and difficult to handle. The surface is sufficiently reflective and flat to achieve good telescope guiding. The clear slit fits on the intermediate inclined support UV06 (the graved face is turner toward the mechanic support):


The next step is to mount the cylindrical lens in the housing provided in the UV01 case. The convex side should be turned towards the inside of the case.  It is very important that the installation plane of the lens is flat and well cleaned of 3D printing defects and burrs.  The longitudinal position of this component is critical in relation to the other optical components (and no adjustment is provided here, the positioning is obtained by construction).  It is not recommended to glue the lens to begin with. It is best to fix it with a quality tape, Kapton, which adheres well both on glass and on the plastic case.

The name “Kapton” is a trademark. It is a polyamide adhesive tape with remarkable mechanical, adhesive and chemical properties. It is often used in optics or to fix elements in environments as difficult as satellites. It’s easy to find this tape from merchant sites like Amazon, hardware shops or electrical hobbyist outlets. You must be careful not to dirty the optical surface during handling (if this happens, clean the glass surface by rubbing with cotton moistened with water then dry, frequently changing the cotton):

It is now time to deal with mirrors M1 and M2. They are arranged in their respective mounts (tighten the side screw gently):

The mirrors in their frames are then fixed in the support parts UV09 and UV10 (embed the FMP1 frames fully in the supports in order to line up the correct height for the optical axis):

You are now ready to mount the mirrors in the UV01 case. Note the presence of pre-positioning marks. Their appearance here is shown with white paint, to make them clearly visible:

Left, the positioning of the supports for the optical components with respect to the markings on the case.

Each of the mirror brackets is mounted with a M4 through screw. The edges of the supports are best aligned at first with respect to the position marks of the housing. The supports are equipped with a link system for fine adjustment of the mirror orientation (UV11). These elements can be moved using a screw that pulls and pushes, controlled from outside the box after slightly loosening the screw fixing the mirrors. Below is a view of these adjustment devices on the external side of the box.

Details of fine orientation tuning system of M1 and M2 mirrors: 

The last element to put in place is the diffraction grating in the UV12 support. Be careful to respect the direction of the arrow drawn by the manufacturer in relation to the support, as indicated in the photograph on the left below (the arrow gives the direction of the blaze). Also be careful to always hold the grating by the sides. Never touch the optical surface. Never rub it for cleaning. If there is dust, leave it, do not try to remove it. Tighten the M3 screw at the top of the UV12 support only quite gently (the use of a nylon screw is ideal, to avoid damaging the glass). Pass the axis of the grating support through the hole provided in the box, taking care not to put your fingers on its optical surface or that of other components – measure your gestures well. Align the support with respect to the mark drawn in the floor of UV01 (valid for a 300 lines/mm grating):

Fit the UV13 external orientation knob using the axial screw so that the rotation is relatively smooth and tighten the side screw so that the grating is well driven. During normal use of the spectrograph, you should turn this knob (slightly) to position the desired wavelength range on the sensor’s sensitive surface.

All that remains is to close the UV01 box with the UV02 cover, then slide a camera almost completely into its place in the camera mount, and you have finished construction!

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