TV scale

  The TV system has nominal scales for various focal setups. The actual scale is defined by a multiplicative correction factor, which is downloaded by the Instrument Control Software on startup. An incorrect scale of the Finder TV will cause difficulties with the location of guide stars.

1. To check a TV scale, observe 2 stars of known position (so that both are in the field of view of the TV in question) and use the CALCULATE DISTANCE option of the Grinnell TV system menu to compare the measured separation with the true value (in both coordinates). Alternatively offset the telescope in order to displace the same star over a known distance on the TV screen.
2. To redetermine the scales, set the scale factor to 1.0 and measure the separation as above. The scale factor is the ratio between the true and measured values in each coordinate.