I have called my CFF 160 F6.5 an excellent scope in search of a good Bino-viewer/corrector combination.
Well, I found one. Big time.
I had the CFF out last night principally to align my AP900 GTO (using the daytime technique but at night with a star). Having done that I turned the scope first to Jupiter, then Saturn. I started with the "Zeiss Biggest" viewer with Baader 1.25X and 1.7X GPC's with my AP diagonal. I mounted the GPCs down in to the 2" adapter and quick changer assembly that Denis Levatic provided. The seeing was really rather calm and I started with the 1.25X GPC but quickly ramped up to the 1.7X jobbie. Wow, Jupiter was engrossing and I quickly maxed out my available eyepiece power with my humble 9mm UO orthos (~195x). Lots of belt detail when the seeing locked in. Went over to Saturn. Very, very nice with that etched quality Saturn has with Cassini, the globe shadow and the ring boundary against the blackness of space. Belt detail on the globe too. Very nice.
So off to Vega which displayed surprisingly good color correction, better than when using the Zeiss with my Denk power switch. Spherical correction was first rate too but there were obvious color differences between the inside and outside of focus ring patterns. But focus, was better than expected with just a bit of red/blue splashing around the stellar core (which was rather white) during moments of unsteady seeing (which was typically induced by my air conditioner's plume when it came on. I had to look over it). The double/double was superb.
Still retaining the 1.7X GPC, I then swapped out the Zeiss "biggest" for the Zeiss "sharpest", also from Denis. This viewer has a mirror with a shorter prism light path but an overall slightly lower light path than the "biggest" viewer. In previous comparisons I've noted the "sharpest" viewer was indeed sharp (but not all that sharper really than my Denks or other Zeiss viewers but still very, very subtly sharper).
Oh my! The double double was very sharp with hard white stellar cores with very faint first diffraction rings. Just wonderful. So, back to Vega.
BAM! I was taken a bit aback by the lack of any color splashing and the intense white stellar core. Ramping through focus showed notably less color tint difference than with the Zeiss "biggest" (or my Denk II which I tried later). Turning to Saturn, it was very, very sharp and even a tad more "etched" with a tiny bit less lateral color than with the Zeiss "biggest". Inserting the 12mm Claves brought the magnification down to the point where I found it difficult to detect any differences in color rendition between the viewer with no differences in sharpness.
I then covered the scope, came inside and got back up this morning to look at the Moon.
Wow (!), just an amazing view with the "sharpest", 1.7 x GPC, AP diagonal and 9mm UO orthos. Very steady seeing. The scope and optical train had all settled down during the night and what really struck me front and center were the sharpness and total lack of color tinting, refraction, fringing, splashing or whatever on the brightly lit rims of crater walls or their central peaks. I find this to be a very demanding test, right up there with Vega and Sirius. Speaking of which, I was struck again by the lack of color splashing and the intense whiteness of Sirius's stellar core. Racking in and out of focus did show some color but of the same tint on each side with identical rings and an excellent collapse down into focus from each side. Wow, true APO performance. I found myself looking around for my 7mm UO pair but couldn't find them.
Speaking of Sirius, the Pup was easy. However, due to the older coatings inside the viewer, Sirius had two other "companions" due to internal reflections (Vega was a triple system ). This annoys some, but I ignore it.
One more final treat was that there was a tight double star just off of the lunar northern terminator line, maybe 1/10 a degree or so. Just beautiful with a white core to the primary and blue/purple for the much fainter companion.
So, after this long dissertation, I have indeed found the "right", synergistic, high power bino-viewer system for this scope: Zeiss "sharpest" from Denis Levatic and the Baader 1.25 and, especially, 1.7x GPCs.
I had suspected this might happen as I had similar experiences with my old AP 178 F9, pre-ED Starfire and TEC 160 ED, using the Zeiss Biggest and the GPCs, but not to the "degree" I experience with the CFF and the "sharpest." I will have to revisit those scopes with this combination.
So when Baader and AP say the correctors compensate, for the slight spherical over-correction and color errors the prisms in the viewers create when using fast APOs, they seem to be spot on, and, in some cases, such as with my CFF 160 F6.5 (which is very fast for the aperture), it's rather obvious.
Like in my audio hobby, I love finding the right combination of components that really lets the music out and helps keeps the nasties in the background. I found such a system for the CFF last night and this morning. Visual "music".
Edited by Jeff B, 22 September 2019 - 09:43 AM.