From jmonnier@cfa.harvard.edu Tue Apr 30 11:06:13 2002 Date: Tue, 30 Apr 2002 11:05:19 -0400 (EDT) From: John David Monnier To: John David Monnier Subject: Stroke->OPD Memo. JD Monnier 2002April11 -------------------- This memo is meant to document, to the best of my ability, how to extimate the true variation in OPD for early IOTA3/IONIC DATA which suffered from various code limitations and a few bugs. Observing dates: 2002Mar06->Mar23 Could be somewhat variable since the angle used by the IDL code was not necessarily stable. Most of the time the AOI used was 10.2 degrees. to get close tot he right true opd for sd1, take opd1 from the written logs, multiple by cos^2(10.2 degs) then multiply by 1.1 (fudge factor in IDL). Observing Dates: 2002Apr04->2002Apr08 pre-"big header" still using fixed AOI 10.2 degrees and wrong formula (wrong one opd=2*stroke/cos(aoi)) Use above formula (not sure about 1.1 fudge, probably should apply this factor..) Observing Date: 2002Apr09->2002Apr12 post-"big header" pre-"angle fix" AOI 10.2 degrees was used in code and in IDL. But used incorrectly (opd -> 2*stroke/cos(aoi) instead of opd->2*stroke*cos(aoi) -- although slightly more complicated because the piezo is pushing slightly non-normal to mirror surface. in Header: Stroke correct, but OPD not correct [no fudge factor in IDL was used, so to find true opd multiply that in header by cos(actual aoi) * cos(10.2 degrees) Observing Dates: 2002Apr13-> in Header: Stroke correct and opd for SD1 is almost correct using opd = 2*stroke*cos(theta=10.4 deg). the SD2 OPD is slightly over-estimated because the AOI is actually a few degrees higher than the 10.4 degrees assumed. Although I think the math is now correct (mostly), the fringes in SD1 do seem to appear a slightly lower frequency than expected... will investigate further. ------ Reference: >From Wes' measurement of IONIC3 9.68 deg AOI for F, 10.86 deg AOI for D1, and 13.32 deg AOI for D2. JPB measured also -- will appear here someday.