Mirror Alignment of the FACT telescope
Our FACT telescope has a multi mirror reflector of 30 single hexagonal mirror facets. To feed our G-APD camera with high resolution images, the reflector's mirrors have to be aligned. The mirror alignment is about the mirror's position and it's orientation.
Mirror Position
The mirror position is fixed in directions perpendicular to the telescope's optical axis by the honeycomb grid of the mirror facets. The crucial position left is the distance of the mirror's centre to the centre of the camera window. The distance between the mirror centre and the camera window centre is determined using a LASER distance meter. As decided on our General Meeting 2014 in Dortmund, we will set this distances to obtain a hybrid reflector. A hybrid reflector is partly a Davies Cotton design and partly a Parabola design. This was chosen to improve temporal resolution.
Status of Hardware for position determination
| Item | designed | ordered | machined | note |
| Optical table | 100% | 100% | 75% | weight reduction |
| 45DEG mirror | 100% | - | 100% | plane,front coated mirror |
| 45DEG mirror mount | 25% | - | 0% | plane,front coated mirror |
| Protection shield | 0% | 0% | 0% | to protect the G-APD window |
| LASER DM (distance meter) | - | 100% | - | Bosch PLR 50, 2x (one spare) |
| LASER DM camera | - | 100% | - | Sony CCD analog for remote readout |
| LASER DM monitor and transmission | - | 100% | - | Monitor for remote LASER DM readout |
| LASER DM mount | 50% | 100% | 25% | motorized mount for radio remote control |
| 2x actuators | 100% | 100% | 100% | 6V DC motor 1000:1 for rotation and altitude |
| Radio remote control 2Ch. | - | 100% | - | 40Mhz analog FM 2Ch. RC transmitter to remote control the LASER DM |
| Battery packs | - | 100% | - | 6V and 9.6V AA GP recyko cells |
| Battery charger | - | 0% | - | charger for AA batteries |
| small stickers ~2cm | - | 0% | 0% | A sticker for each mirror's centre |
| thin rope | - | 0% | 0% | to position stickers |
Mirror Orientation
The mirror orientation will be dealt using the Bokeh approach. There is a video of the Bokeh technique performed on Mini FACT in the \home of the GATE PC on La Palma.
Status of Hardware for orientation determination
| Item | designed | ordered | machined | note |
| Lamp | 0% | 0% | 0% | A bright, punctual (<5cm) light source |
| 2x 3m tripods | - | 0% | - | A tripod to place the lamp, camera or the cross line LASER on (photo thread) |
| tripod | - | 0% | - | A tripod to support the G-APD camera housing while alignment at zd=90DEG |
| 2x Cross line lasers | - | 100% | - | self level cross line lasers to set the optical table |
| Bokeh plate | 0% | 0% | 0% | A plate to place the Bokeh template on (MDF 40cm diameter) |
| Printer | - | 0% | - | A printer to print the Bokeh template (DIN A4 inkjet) |
| machine grease | - | 0% | - | A non water dissolvable machine grease to minimize breakaway torque in the mirror joints |
| grease remover | - | 0% | - | To remove surplus grease after alignment |
PSF determination
To determine the Point Spread Function (PSF) of the telescope, the PSF camera will be used. The PSF camera has a huge image sensor of 60mm x 60mm and 1MPx. The PSF can be determined in the centre of the camera window or offset the centre. The PSF camera can handle light fluxes on approx. 4 orders of magnitude.
Status of Hardware for PSF determination
| Item | designed | ordered | machined | note |
| PSF camera | 100% | 100% | 100% | A 3D printed camera with 60mm x 60mm sensor area |
| 25m active USB | - | 100% | - | A cable to read out the PSF camera using a PC/Notebook |
| Computer | - | 0% | - | A Notebook running the PSF camera driver to readout and display the PSF camera |
Maybe the PSF camera might be used for additional ultra fine alignment. On Mini FACT this technique was used once and worked out quiet well in combination with the PSF camera. Anyhow this is not necessary when the Bokeh alignment has been performed calm and careful. A blocking shield is used here to block a single mirror to locate the mirror to be fine aligned.
| Item | designed | ordered | machined | note |
| Mirror cover | 0% | 0% | 0% | A cover made of cloth or MDF to cover a single mirror (not touching the mirror) |
Tools
hex key driver, open and closed end wrenches, thread locking fluid
