Thanks David, Adam, Peter, Russel, Michael and Adam for Very kind comments!
I aimed to get some more details of the outer shell, but it appeared very slightly. Later I got an off-axis guide and now 20-minute exposures are not a problem but during the shooting of this frame I was yet limited by 3-min subs with flimsy guider mounting.
It would be interesting to take additional several hours via 20min subs and compare SNR with same total time sum of 3min subs. It was is about 20% difference measured by bright objects SNR, but I suspect strong non-linearity for faintest details in heavy light pollution conditions because mathematics became non ideal suffering from all accumulated errors (non ideal calibration, non constant non flat sky background, etc)
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That's a lovely sounding scope too... reducing it to F6 would have helped too.
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Yeah, this OTA has it's own story. In 2007-201x I was kind of NPZ's Ambassador & volunteer tester and they provided it to me. I visited them in Novosibirsk several times, so had a chance to personally got acquainted with Yuri Klevtsov, and developer engineers of TAL telescope series Lev Parko and Anatoly Ageev.
The factory at that time had produced a small series of 0.7 reducers/flatteners "Mk1" explicitly calculated for TAL-250K and APS-C matrices. I tested them on the sky, and then I got a new Mk2 for tests, which was a prototype (never sold, only few items produced and some distributed to amateurs).
