When I saw that Denis Levatic was exiting the bino-viewer business due to personal reasons, my heart went out to him. I was in a similar circumstance myself just 9 short years ago.
I've been a customer of Denis's since he started. He was "super charging" existing viewers (collimation and where possible, expanding a viewer's light path clearances). I got a very nice sample of a Super Charged Baader MK V from Denis in 2016. That was quickly followed by several other viewers, all Zeiss based, including two versions of the CZAS viewer. All have been optically and mechanically excellent. Some of these viewer's bench performance has been documented here:
That thread will be expanded shortly with additional samples.
The subject of this thread is to document the bench and visual assessment of Denis's latest iteration of the CZAS with the FDAS/RSCS Diopter System. FDAS stands for Fine Diopter Adjustment System while RSCS denotes Real Self Center System. When Denis's stock of these viewers is gone, there will be no more made so I ordered one.
Bill P here wrote up an extraordinary description and review of an earlier CZAS sample which used Baader Click Lock Diopters early last year :
My FDAS/RSCS version is essentially identical to Bill's except for the new diopter system designed and developed by Denis.
Please refer to Bill's thread for a very detailed description. I certainly appreciate their light weight and solid all metal construction. However, this sample is also beautiful, with flawless fit and finish, very attractive. The photos simply do not do justice to their immaculate physical appearance. The understated blue Zeiss badge which covers the tension adjustment is a nice touch.
The measure optical path length of each side to the tops of the diopters were 133mm which agrees with Denis's spec.
Now the diopters and I'll cut to the chase here. These are the finest diopters I have used. Period. My previous favorites where decidedly the Denk Binotron's diopters for their smooth, linear, positive action, and good grip on the eyepieces. The FDAS/RSCS Diopter System takes what the Tron diopters do well and pops it up to a higher level of smoothness and ease of adjustment. They really do self-center. And they consistently pull off a trick I have not encountered in any viewer diopter system....they seem to be able to handle the tapered under cuts on my Sterling Plossl eyepieces with precise, stable eyepiece centering and image merging. Impressive! Stay tuned on that. Individual diopter focusing is silky smoooth and precisely up and down. Collimation is perfect for me with this sample.
We have had some excellent, stable seeing around here this summer and I have taken advantage of that with extended sessions with this viewer on Jupiter, Saturn and some of the usual suspect summer stars such as Vega, Altair, Double-Double and Albireo. The context for my assessment of this viewer has so far been my usual system which is my TEC 200ED triplet + AP Maxbright diagonal with the CZAS viewer plugged into an excellent Denk Power Switch system (dual arm power switch plus OCS element plugged into the 2" nosepiece). How do I know the Denk switch/OCS system is excellent? I have DPAC . My most used eyepieces were my Denk 21 LOA Neutral pair and, briefly, my Sterling 20mm Plossl pair.
Again, I'll cut to the chase here too. This is optically the finest viewer I have used. Period. Some of my other viewers are excellent (which I'll get into later in the comparisons section) but this sample CZAS with these diopters is subtly but noticeably superior in almost every regard.
I started with stars while waiting for the gas giants to roll around to better viewing heights. Vega was intense at ~230X with a well defined white-ish airy disk and NO red and blue splashing around it during moments of turbulence. Scatter/glow and junk around the star was very low too. At the same magnification, the double-double were two hard, sets of beady little eyes staring back at me with a faint, uniform diffraction ring system around each. Just excellent. Albireo was, ok, ok, I'll say it, "jewel like" with an intense red and blue. The other intense thing I noticed was the blackness of the background space. This really set the pair and the other stars in the FOV apart from the "intense" black around them. Just beautiful. Altair, like Vega was intense with a sharp airy disk and uniform first diffraction ring with scant scatter.
Saturn was "etched" during moments of very steady seeing. Cassini's division and the planet's shadow against the rings were chiseled jet black. Fine color gradations and structure spanning the rings were readily seen as was Enke's minima during the steadier moments. The planet's globe gave up just a beautiful color pallet, looking like a hard boiled egg yolk suspended in space. There was NO hint of "CA". Titan was a very small, very faint salmon colored distinct disk.
Jupiter was similarly detailed and sharp and BIG, with again, NO "CA", in fact, even atmospheric dispersion seemed subdued too, especially around the moons.
Now I've seen some extraordinary views like this with other viewers too (which I will get into later with comparisons) but there was a certain, hard to describe, sublime intensity and sharpness I saw when using this CZAS.
Were they perfect? Close but no. Like most other viewers, there was a color balance difference between the right and left sides of the viewer. This was best seen on Jupiter which had a slight but distinct, yellowish tint on the left side compared to the cooler right side. Even Vega, displayed a mildly yellow-ish core at high power on the left side compared to a very white core on the right side. However, when using both eyes, I really could not detect anything amiss. I've seen this R/L color tint difference with many other viewers (but not all) before and I'll discuss it some more during the comparisons section.
Up next I'll talk about some comparisons with other, high-end viewers.