Topic/Presenter: Opto-mechanical / M. Vincent

Question/Comment: 

Include a shutter: It is needed for:
 - Planetary science
 - Shift & add to "freeze" seeing & improve PSF on
   on bright sources
 - Calibration on bright standard stars (e.g. Elias standards)


Submitted by:  John Bally


NIC-FPS Response:


We have considered adding a (cryogenic) shutter but currently do not
plan to implement one for the following reasons:

- Cost: Given the optical design and plan for optics mounting, the most
accessible region is near the entrance window of the dewar. The shutter
would need to be about 120 mm clear aperture, which would not be a
cheap item.

Locating the shutter immediately in front of the Focal Plane Array
makes for the smallest possible shutter (~25mm diameter) that
effectively blocks scattered light and works for both modes.  The
downside of this location is very limited space (<13 mm) between the
last lens and the FPA.

- Detector read-out performance: The H-1RG detector we are procuring
from Rockwell supports read-out modes from 200 kHz to 5 MHz (2 output
channels). Thus for bright targets, the entire array can be read out
in about 0.1 s. In addition, the H1RG can be programmed to read out a
selectable sub-array with even shorter integration times. (For example,
Jupiter subtends only about 1/20 of the total FOV.)

A blank will be located in a filter wheel for dark frames.

Status: Closed.