Only six SM140's - so far the largest commercial production H alpha filters - were made by Coronado Tucson -- three by Andy Lunt and three by Brian Stephens (both now with Lunt Solar of course), and only two were equipped with double stacking modules. One (allegedly with an internal SM60 module) is used at the Vatican Observatory in Rome, and the other was presented at Hands On The Sun (HOTS) in Tucson late in 2005 using the SM90 internal module installed in a TAK FS 152 f8, as shown here:
I was able to view through it first-hand then, and the image was pretty darn awesome. I recently informed Greg Piepol (who also attended) about getting this set, and he remarked
I will be putting this system together with a 150 f8 achromat (no real need to use a Fluorite APO), and as luck would have it (just as with the SM90) the filter threads for the T-Max tuner are identical the objective cell, and no front filter adapter is necessary:Boy, do I remember that SM140! I skipped a talk at HOTS 2005 to spend some quality time looking through it. In all my years, that filter combination was the best solar view I've seen.
The internal module outer rings are removable, and can be easily adapted to the new OTA inside diameter once the internal baffles are removed, and the tube shortened slightly for bino-viewer use:
Given the ratios of the objective effective aperture to etalon are similar to the ratio of the objective to collimator focal length, a field angle magnification can be estimated at 140/90 = 1.6, therefore the field angle of the sun’s limb should subtend only about 0.25 x 1.6 = 0.40 degree, well within the diameter for pretty good full-disk contrast uniformity. Regardless, I’m looking forward to the increased resolution; and the existing SM90 system will be kept if needed for full-disk work. I will keep my progress posted.