Technical Data - Mechanical

The Basic Stucture

From the very outset of this project we had several objectives in mind:

With these criteria in mind, Christian opted for a Littrow configuration for its compactness (a folded optical axis) and also for cost (the dual role of the collimator/focusing lens eliminate the need for 1 component).  From that basic premise, we also made other important choices at an early stage:

  1. The spectrograph body is in folded sheet aluminium.    
    This method of fabrication is well adapted for short series mass production, with the various pieces manufactured by CMC methods from CAD data files, resulting in a good compromise between production cost and component functionality. Assembly of the differnet pieces of the external body panels achieves the required high rigidity whilst minimising weight. Sheet metal screws are used to fix the various body panels in order to avoid the problem of threading holes through the aluminium panels which are only 1.5mm in thickness - this would have been too difficult a task with many stripped threads at risk!
    The core structure of the instrument, based on sheet metal, means that the different modular components (camera mounts, slit and grating supports, the lens mount, etc.) can all be designed independently, thereby creating the desired modularity.
    In order to limit the types of screws used, we decided to use M3 metric screws for the assembly of the basic chassis and M4 screws whenever any  additional mechanical strength was required or whenever frequent screwing and unscrewing would be needed.
  2. The choice of Reflective Slit:     
    Due to the narrow slit widths to be employed with this spectrograph, some mechanism for guiding become quickly apparent. A reflective slit is more complex to manufacture (especially for mass production) but it has the advantage over the semi-reflecting type that no light flux is lost. We therefore preferred and selected this option. André Rondi performed the initial critical trials on a brass slit, and his approach guided the way. Then Patrick Fosanelli took up the challenge of making stainless steel slits (harder, more durable), taking particular care with the flatness and smoothness of the jaws. It is thanks to the talent and ingenuity of André and Patrick that we have been able to achieve an instrument with these performance characteristics!   

  3. The possibility of including a DSLR
    Quite quickly Christian was adamant that Lhires III should be capable of being used with large format digital single lens reflex cameras. Although it is true today that cooled CCD cameras are significantly more sensitive than DSLRs, this consumer-driven market is driving the cost of DSLR's down and improving the technology to the extent that more and more amateurs will be using these cameras in the future.
    Providing support for DSLR's did not turn out to be as straightforward as we thought. The dimensions of these cameras and the fact that the CMOS sensor is situated towards the rear of the body and about 50mm from the camera adapter at the spectrograph requires a telescope with plenty of back-focus. In order to keep the system compact still, we had to be more than a little cunning and get the telescope beam to come very close to the main faceplate of Lhires III (where the webcam / CCD guide camera are mounted). This explains why there is a shift in the position of the mounting plate on the telescope (see the photo of the prototype with a DSLR attached on the "Prototype" page).    Despite this, we got there in the end and with no regrets since it all works !
  4. An Integrated Neon Calibration Lamp
    A small Ne lamp for the wavelength calibration of spectra is integrated in the design. Neon has the great advantage of several several strong emission lines around H-alpha. Initially, this lamp was supplied with mains voltage (220V). Safety considerations, however, led us to design a small circuit to drive the lamp from a 12V source. Fortunately, there is always a 12 volt source around a telescope these days!

3D Schematics!

Technical drawings are available in PDF, DXF and SolidWorks format. There can only be used for personal, non-commercial purposes. Here is an extract in JPG format:

d_2006-01-25 VisuButeeMax - Feuille1.jpg d_2006-01-25 VisuButeeMin - Feuille1.jpg d_Bague-T Montage CCD-3 - Feuille.jpg
 d_2006-01-25 VisuButéeMax - Feuille1  d_2006-01-25 VisuButéeMin - Feuille1  d_Bague-T Montage CCD-3 - Feuille
d_CI1-2 - Feuille1.jpg d_DemiFente-3 - Feuille1.jpg d_Lhires3-Configs - Feuille1.jpg
 d_CI1-2 - Feuille1  d_DemiFente-3 - Feuille1  d_Lhires3-Configs - Feuille1
d_Lhires3FC-3 - Feuille1.jpg d_RefOptique-3 - Feuille1.jpg d_RessortReseau-2 - Feuille1.jpg
 d_Lhires3FC-3 - Feuille1  d_RefOptique-3 - Feuille1  d_RessortReseau-2 - Feuille1
d_SchemaNeon.jpg t_CadreReseau-3 - Feuille1.jpg t_Cale-1 - Feuille1.jpg
 d_SchemaNeon  t_CadreReseau-3 - Feuille1  t_Cale-1 - Feuille1
t_ChassisTole-4 - Feuille1.jpg t_CouvTole-6 - Feuille1a.jpg t_CouvTole-6 - Feuille1b.jpg
 t_ChassisTole-4 - Feuille1  t_CouvTole-6 - Feuille1a  t_CouvTole-6 - Feuille1b
t_DosReseau-6 - Feuille1.jpg t_EtrierReseau-6 - Feuille1.jpg t_FLASQUED-4 - Feuille1a.jpg
 t_DosReseau-6 - Feuille1  t_EtrierReseau-6 - Feuille1  t_FLASQUED-4 - Feuille1a
t_FLASQUED-4 - Feuille1b.jpg t_FlasqueG-4 - Feuille1a.jpg t_FlasqueG-4 - Feuille1b.jpg
 t_FLASQUED-4 - Feuille1b  t_FlasqueG-4 - Feuille1a  t_FlasqueG-4 - Feuille1b
t_LREF-8 - Feuille1a.jpg t_LREF-8 - Feuille1b.jpg t_Supp1MiroirWebcam-3 - Feuille1.jpg
 t_LREF-8 - Feuille1a  t_LREF-8 - Feuille1b  t_Supp1MiroirWebcam-3 - Feuille1
t_Supp2MiroirWebcam-3 - Feuille1.jpg t_SupportFente-4 - Feuille1.jpg t_Trappe-3 - Feuille1.jpg
 t_Supp2MiroirWebcam-3 - Feuille1  t_SupportFente-4 - Feuille1  t_Trappe-3 - Feuille1
u_2006-01-25 Bride Telescope.jpg u_AxeButee-3 - Feuille1.jpg u_AxeEcranNeon-3 - Feuille1.jpg
 u_2006-01-25 Bride Telescope  u_AxeButee-3 - Feuille1  u_AxeEcranNeon-3 - Feuille1
u_AxeSuppReseau-3 - Feuille1.jpg u_BagueInt-2 - Feuille1.jpg u_BagueMaintienDoublet-1 - Feuill.jpg
 u_AxeSuppReseau-3 - Feuille1  u_BagueInt-2 - Feuille1  u_BagueMaintienDoublet-1 - Feuill
u_BagueMeade_C8-2 - Feuille1.jpg u_BrideAudine2-1 - Feuille1.jpg u_BrideButee-6 - Feuille1.jpg
 u_BagueMeade_C8-2 - Feuille1  u_BrideAudine2-1 - Feuille1  u_BrideButee-6 - Feuille1
u_BrideDoublet-2 - Feuille1.jpg u_BrideM42APN-6 - Feuille1.jpg u_BrideST7-2 - Feuille1.jpg
 u_BrideDoublet-2 - Feuille1  u_BrideM42APN-6 - Feuille1  u_BrideST7-2 - Feuille1
u_BrideTelescopeFC-3 - Feuille1.jpg u_Carre-4 - Feuille1.jpg u_EmbaseMiroir-2 - Feuille1.jpg
 u_BrideTélescopeFC-3 - Feuille1  u_Carre-4 - Feuille1  u_EmbaseMiroir-2 - Feuille1
u_EmboutButee-1 - Feuille1.jpg u_FourreauAudineST7-1 - Feuille1.jpg u_FutDoubletWebcam-4 - Feuille1.jpg
 u_EmboutButee-1 - Feuille1  u_FourreauAudineST7-1 - Feuille1  u_FutDoubletWebcam-4 - Feuille1
u_FutNeon-3 - Feuille1.jpg u_PiedMiroirRenvoi-2 - Feuille1.jpg u_Porte-oculaire-2 - Feuille1.jpg
 u_FutNeon-3 - Feuille1  u_PiedMiroirRenvoi-2 - Feuille1  u_Porte-oculaire-2 - Feuille1
u_SuppCollimateur-3 - Feuille1.jpg u_SuppFente1-3 - Feuille1.jpg u_SuppFente2-3 - Feuille1.jpg
 u_SuppCollimateur-3 - Feuille1  u_SuppFente1-3 - Feuille1  u_SuppFente2-3 - Feuille1

You can also download this programme (Windows, 2.4MB) that displays the 3D schematic drawings and allows you to rotate the spectrograph at explore the internal design.


drw_RefOptique-3 - Feuille1.jpg drw_Lhires3FC-3 - Feuille1.jpg
Optical Schematics & 3D schematics

plan3db01.gif plan3db02.gif plan3db03.gif
plan3db04.gif plan3db05.jpg plan3db06.gif
plan3db07.gif plan3db08.gif plan3db09.gif
plan3db10.gif plan3db11.gif plan3db12.gif


Mechanical Interfaces

Lhires III has been designed to be easily connected to a wide variety of telescope configurations.  Let's have a look in some detail at the different possibilities.

drw_Lhires3-Configs - Feuille1.jpg
Schematic drawings of the Adapters
(pdf file still in French)

1 – Coupling to the Telescope

Lhires III comes with two coupling adapters: one is 50.8 mm ring for direct connection to the rear thread of the popular SCTs by Celestron (C8, C11, C14,..) and Meade (LX200, LX200 GPS,..). The other is a 2 inch (50.8 mm) tube adapter.  You can also make your own adapter tube or ring which is then attached to 6 countersunk M4 screws (refer to the drawings below - the notes are still in French, but a picture says a thousand words!).

drw_BagueMeade_C8-2 - Feuille1.jpgdrw_SuppTelescopeCoulant50.8-4.jpg

2 – Coupling to the CCD Camera

 Several camera adapter rings are also supplied with the kit for connecting to the following CCD cameras:

drw_Bague-T Montage CCD-3 - Feuille.jpg
CCD Camera adapters (still in French)

3 – Connecting a Guide Camera

Several kinds of guide camera can be employed. The initial tests were performed with a webcam (Vesta Pro), with a tiny security video camera and also with a high sensitivity integrating video camera (Watec 120). All these cameras use a 1¼ inch (31.75 mm) thread and so this is the only one supplied with the kit. For webcam's such as the Philips ToUcam, an adapter is readily available commercially. For any other type of guide camera, you must provide your own, noting that the distance to the video chip in most cases is 53 mm.

Neon Lamp Power Supply

Here you can see the small PCB that is used to convert 12V dc to ~100V AC to drive the Neon calibration lamp. It is mounted on the switch assembly.

plan_neon_ci.jpg DSCN6753.JPG