Well ... first of all the VMC or VCL design is not a Klevtsov design. Yes, both designs use subaperture correctors (and I think both are all spherical telescopes) but the details, especially within the so called “corrector unit” are different.
To be honest the VIXEN designs doesn’t convince me at all. The practical experiences of the VMC/VCL often reported thermal issues of the tube, sometimes quite “fat” bright stars due to the straight and quite thick spider veins and occasionally collimation issues.
But the Klevtsov design is quite sensitive too. To achieve an all spherical design the lenses within the corrector are quite extreme and their radiuses and tolerances are really very small. Unfortunately this leaded to a widespread manufacturing quality. Some TAL-Klevtsovs suffer from severe spherical aberration, downgrading their performance seriously below diffraction limited quality, some are barely diffraction limited. “Photo quality” ... would someone in Moscow say, who is regularly testing telescopes, Klevtsov’s too ...
On the other side - have a look at Dimitry Makolkin and his moon images:
or here at CN, too.
Looking at his images is the cheapest way getting a ticket into a lunar orbit 😜 ...
He uses a serial model TAL-250K for his extraordinary pictures. Of course he is brilliant in image processing, but with a lemon tube you can’t achieve these results. Anywhere he published the interferometry of his TAL-250K: As far as I remember about 0.9 Strehl - definitely a good one, but no phenomenal quality.
From my point of view the Klevtsov design (if the spherical aberration is under control) provides very crisp star images (what I would call “refractor-like”). Open clusters, star fields are a real pleasure. Very bright stars show a little halo, but due to the curved veins, quite well covered. The thermal equilibrium is as well much much better compared to the VIXEN subapertur tubes I have seen. Compared to a SC or VMC/VCL the Klevtsov images look a little bit fainter (there are many glass elements light has to pass till it reaches your eye). The central obstruction is about 35% (linear), so “blurred” images on planets (compared with a 7 or 8” unobstructed telescope) are unavoidable. But that’s in common with any other obstructed telescopes.
My conclusion is quite simple: If you own a good diffraction-limited Klevtsov type telescope (let’s say about RMS 1/18-1/20 lambda/wave) you will love it - definitely. It’s a precious keeper! BUT thats only the the half of truth. The other half is: You’ll have to find a diffraction limited Klevtsov.
Edited by Andreas-TAL, 30 August 2018 - 04:00 PM.