He found the FWHM bandpass was 0.64A (0.68A as measured in the Ha line) and the tilt 0-1.3 degrees moved the CWL from +0.46A (red wing) to -1.2A (blue wing) (based on the Ha line) This allows a doppler shift imaging from +21 to -55 Km/s
Hi Ken,
That is great information - also in keeping with the idea that a tilt-tuned etalon should be designed so that minimal tilt is needed to bring it on band.
Most of the early DS attempts with Tucson Coronado etalons fall in this category - the "matching" process was intended to insure that via random variation the etalon requiring the least tilt was used as the primary, and an etalon that needed more tilt was used as the secondary. This was referred to as secondary etalon "pre-tilt," and it was therefore hoped that little, if any, additional tilt would be needed to get the secondary etalon on-band. It also demonstrates that when using an etalon intended for single filter use it might end up in the blue wing following ghost removal and not able to be brought further on-band if the CWL is very close to the H alpha line (hence the need for "matching.")
While it also might be random variation, it seems the more recently purpose-made double stacking etalons are designed with a CWL which is significantly higher, and I have experienced more than one that did not come on-band even at maximum tilt. If this higher CWL is the case with the Rich View etalons, they might be tuned high enough as to remove ghosts by tilting, and still remain slightly "high" and can be brought on-band by compression of the spacers.
IF that is the case then these might be superior to etalons tuned by tilt alone.
Again I have no experience with these Rich View etalons. It would indeed be nice to see what they measure out as for design CWL (zero tilt).