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)

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)