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.
© ALCOR SYSTEM
| Diameter |
Ø52 |
Ø72 |
Ø100 |
| Material |
BK7 |
BK7 |
BK7 |
| Anti reflexion coating |
MgF2 |
MgF2 |
MgF2 |
| Surface flatness (PV) |
λ/4 |
λ/4 |
λ/4 |
| Deviation angle (min) |
1 arcmin |
0.7 arcmin |
0.7 arcmin |
| Deviation angle (max) |
9 arcmin |
9 arcmin |
9 arcmin |
| Thickness |
12 mm |
18 mm |
22 mm |
Limiting magnitude (1) |
3.2 |
4.4 |
4.8 |
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Celestron 8,9 & 11 telescope
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GSO 300 and GSO 400Truss and tube
And much more ....
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 :
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 prisms
Note 1 : 10 ms exposure time - focal length : 950 mm - Green Filter - same night test - 3.8 µm pixel size.
The measurement accuracy will be roughtly the same with these diameter, below a plot that shows the relative accuracy measurements versus R0 (in mm). The benefit of larger prisms is to reach fainter stars located nearby zenith.
DIMM masks for seeing monitor
Custom made masks
