These were purchased from Kitt Peak, as originally specified by J Mould. They have flat-topped profiles and are intended for use with CCD detectors (unlike earlier filter systems). Figure 16 shows details of these filters. Three sets exist; two sets for the ING telescopes and a spare set at RGO. The original specifications are given below:
All filters to be 5cm 5cm, 3mm thick, blocked to 1.1 micron, bett er than 75% peak transmission (except B 70%), MgF coated, no pinholes, optical quality glass.
R: Filter 7200Å= short-pass hard-coated on 3mm OG590, blocked to 1.1 mi cron, 75% or better peak transmission, MgF coated on glass side.
I: Filter 9000Å= Short-pass hard-coated on 3mm RG-M9, blocked 1.1 micro n, 75% or better peak transmission, MgF coated on glass side.
V: Filter 6000Å= Short-pass hard-coated on 3mm GG 495 blocked to 1.1 mi cron, 75% or better peak transmission, MgF coated on glass side. (Sent back did not come up to specification, 1/6/81)
B: Filter 4900Å= Short-pass, hard-coated on the glass substrate indicat ed below, blocked to 1.1 micron, 65% or better peak transmission, MgF2 Coated on glass side. Glass substrate to be cemented combination of Schott GG 385 and either Hoya GM-500 or Hoya C-500 (whichever will adequately suppress the red leak). Total thickness to be 3mm as with the other items.