DIMM masks for seeing monitor
This product is intended to be put at the telescope entrance, and provide a beam deviation, so that to produce two images of the same star, required for seeing measurement using Differential Image Motion Monitor (DIMM). The standard two holes mask is made of two Ø52 or Ø74 mm holes in a laser cut and black anodized aluminium plate. The mask is attached to the telescope.
Custom made masks
Diameter Ø52 Ø72
Material BK7 BK7
Anti reflexion coating MgF2 MgF2
Surface flatness λ/4 λ/4
Deviation angle (min) 1 arcmin 1 arcmin
Deviation angle (max) 9 arcmin 9 arcmin
Thickness 12 mm 18 mm
Celestron 8,9 & 11 telescope
BRC 250 Takahashi
GSO 300  and GSO 400Truss and tube

We have already produced masks for the following telescopes :
Alcor-system can manufacture any mask size, for any other telescope size, provided the user gives all mechanical informations of the telescope entrance.
One of the hole is equipped with a set of tunable prisms, allowing to adjust the two image of the same star at a given distance, to fit as best the field of view of the camera. The angle adjustement is achieved by rotating one of the part. Here are the optical specifications :  
PLEASE ASK US A QUOTE the price depends on telescope size and type
Upon request, any mask size, for any telescope aperture and any hole size and prism diameter (up to Ø120mm)  and beam deviation can be achieved by our company. Please do not hesitate to ask us. 
Left Ø52 mm , right Ø72mm Prism