TAO 130 Benchtest

My TAO 130 finaly and passed my benchtest

1, The telescope mechanics are great as usual. Personly I do not like the tube ring stop for the retractable dewcap, this could be solved by a nicer method

2, Optics. Mine shows even after during cool down a astigmatism, the airydisc is here but with little cross, going either way through focuse you see the astigmatism also clear. After time moving, the astigmatism goes completly away, thats maybe a result of the large airspace , so please allow the telescope to get completly cooled down .
Spherical correction looks rather good , but with some undercorrection as most apos from all manufactors show, which means inside of focuse the fressnell rings are clean and sharp and outside of focuse all fressnell rings are a bit softer.
Using a green filter to see if its optimzed for green show same result, so the undercorrection is not a result of spherochromatism , but of real slightly undercorrection.
I used a red filter and found by red the best correction, so its nulled not for visuel, but for Red, CCD. Since Takahashi say its an CCD image mashine, it is correct nulled.

Coatings: The coatings are very nice and better optizest than in my stocking FS 128

Visual Startest:
- Infocuse: colorfree with bright white airydisc and very faint first diffraction ring
- inside of focuse, a hint of orange
- outside of focuser clearly viaible a outer lightblue colorfringe

The colorcorrection is quite similar to my FCT 150, where the outside lightblue was more a deeper blue.
This color I found is invible for many observers and far brighter in an 140F/7 and 160F/8 Triplet apo I saw some time ago . Last days i sold a used AP 180F/9 EDT which have also a similar good colorcorrection.

Now please do not ask me how it compares to the TMB correction, even if I say the thruth , it would not be fair to state anything about that, because I am a TMB Dealer

Estimation of the final quality ? I can speak about my many years experience only. A eye startest cannot detect smallest local errors which maybe show on a printed document lower numbers, due some smallest local errors. But for global correction, this Telescope shall have over 96% strehlratio and about 1/7 wavefront p.t.v., I could be wrong, but thats my estimation by comparing the startest with telescopes where I have printed testreports.



One last word: The overal correction of this lens include colorcorrection remembers me 1:1 to the Silverstar/TMB designed 130F/7 super apo with 4 elements, such a lens show excact the same colorcorrection



thanks

Markus

update of my test:

I thought 2 hours are enough to do cool down for the 5" to do the benchtest, espacialy , because outside its now much cooler than in our testing room.
But now after 4 hours laying down on the bench , I found that it cooled down extremly long. Now after 4 hours the undercorrection increase and it shows now only around 1/4 wavefront p.t.v. , way worser than the image was after 2 hours cooling.It seems this large airspace really take very long time , so for real critical observers, either such a scope should be permantly in its observatory building, or you must give him real long time for cooling to get the last photon out of it.

Markus Ludes