Kevin_A The lens clicks are at f1.4,1.6,1.8,2.0,2.2,2.4……
Hah, the Rokinon T-stops don't have clicks. Completely smooth, for the follow focus guys.
I too will revisit the FSQ's reducer (330mm f/3.9) and the Vixen FL55 (236mm f/4.3), now that I have the Askar backfocus adjuster (makes life really easy, with calibrated steps of way higher resolution than 0.05mm -- I am now also convinced 0.1mm type backfocus is not good enough to adjust coma out of the corner stars).
Neither of these scopes and their reducers are that fast, but the Vixen was a big disappointment. We'll see how it does after using the backfocus adjuster and new methods of adjusting backfocus.
The Vixen's 236mm is actually a good focal length, in spite of being a little slow at f/4.3 (we should be complaining -- Askar thinks something like the FMA180 with the "Pro" designation is super fast at f/4.5 :-). I am sure there are times I wished I had 236mm instead of 270mm or 330mm.
The Tak's f/3.9 reducer is nowhere like their 1.01x flattener (f/5.4) though, even in Tak's own published spot diagrams. I like stars that pop out at you, and I had not used the f/3.9 reducer much. We'll see if retuning backfocus critically can help. Stars have to pop out at you over the entire frame and not just the central 1/3 of a frame, otherwise, there is no "pop" effect.
You should get your hands on one of the backfocus adjusters. I am going to retrofit it into all of my OTA that have backfocus to spare (about 18mm), and use them as permanent spacers that I can quicky adjust when I change filter thicknesses (and not change camera angle). I have already so far already bought four of them from that Alberta store (they are the only ones in North America that have them in stock, it seems); my original was from Agena.
It is rare when something as good as the Askar adjuster appears in this hobby. I don't know why the YouTube shills have not yet touted it much. Perhaps they have never adjusted back focus in their lives, and have been using the "55mm" like ZWO (and some of the Cloudy Nights' Pleiades 68 owners :-). The Tak's FSQ backfocus is nominally 56.2mm, by the way, and the Vixen (with the flattener + reducer) is an even weirder 63.5mm. 55mm? ZWO must think we are all stooopid.
it was puzzling me why but now with adding the 0.04mm of shims it is directly in the centre of the infinity mark.
Ah, I think you are getting to the true backfocus! Where the lens designer wants you to place the image plane.
Chen
