Staring

You want that star to be far, far closer to focus to check for collimation on axis. You also need to check the off-axis star shapes to be symmetrical. This is because both mirrors are hyperbolic, meaning their optical axes must be very carefully aligned to each other and to your focuser. You can have a good on-axis dtar and still terrible field. Google „DSI collimation method“ for an explanation. This is no SCT or Newtonian and tips and experience with them will lead you astray. Can‘t help much with the Ronchi, but I‘ld you‘re just not collimated enough to get a meaningful reading.

I‘ve looked at the Askar scopes, too. The small ones show a lot of off-axis aberrations, even in the spot diagrams. The Askar 400 looks better, but with the reducer it has significant CA. And I have not seen an image that has great corner stars on an IMX571 sensor with full resolution - this probably means the scope can not do it.

Thanks for helping. Yes, I admit the bar is high. TS telescopes seem to be somewhat hit-and-miss, and it‘s difficult to know which is which. Maybe I can get them (or a reseller) to agree to a bench test and optimization. Concerning the FSQ-85: I also thought it‘ld be the dream astrograph, which is why I bought it. Its shortcomings are documented in many threads, though, if you look for it. For modern sensors with small pixels the field is not well-corrected enough and so it needs its dedicated flattener/corrector, giving up the advantage of the Petzval design. The flattener is now included by Tak (I think since 2019). But even with that I had these diffraction artefacts that look like vignetting, but on on-axis stars. You can also find that on many recent images with that telescope - I see many older ones that do not show it. The reducer really is only usable with pretty big pixels, even if you get the spots that Takahashi advertises. My sample must have some internal misalignment, though. The focuser can not compare to something from Moonlite or Starlight Instruments. The shifting could not be adjusted away. From what I researched about 50% of the Tak focusers have that problem, which is why many people accessorize theirs with 3rd party focusers. All in all the FSQ-85 feels like a dated design that can not hold up to the demands of modern cameras anymore.

Hello everyone, I‘m looking for a perfect small refractor for astrophotography, and so far had not much luck with the ones I chose. The criteria are: - Flight portable, so 48cm max. tube length - FL 300-500mm - no slower than f/6 - very good correction for CA - premium build quality - flat field with good stars up to APS-C with small pixels (IMX571) - dedicated reducer or reducer/flattener preferred - Also usable visually - available new - Budget is high My story to illustrate my expectations (no need to read except to exclude the 61EDPH and Tak FSQ-85): I‘ve first tried the 61EDPH (v1). Its build quality is serviceable. As a doublet it suffers from rather bad CA and my sample also has some SA. The CA makes using it with a mono cam and dual-NB filters very difficult. Then I splurged for a Tak FSQ-85. The initial impression was very favorable: Built like a tank, nice to touch, comparably compact. That didn‘t hold long: The 0.73x reducer had terrible aberrations. With the flattener, stars were ok-ish, but still showed diffraction artifacts around bright stars. The focuser introduced image shift. I‘ve returned the scope. I‘m hesitantly looking at the RedCat (but see many examples of non-flat field and do not like the helical focuser), the Vixen 55FL (which seems to have backspacing issues according to some posts), Borg (CA), the Askar telescopes (CA, aberrations) and the CFF 80mm (only f/6.9: tube too long). Did I miss any other suitable telescopes?

I‘ve had extensive help from the Sitech mailing list sorting out my problems with the factory configuration (that was unusable except for „no pier flip“ configurations - maybe works for an 80mm Apo). The Sitech software has a learning curve, but once I got used to it, I have come to appreciate the functionality and it blends into the background. I did not know about the possibly faulty hand controllers, but I find it strange that one is expected to hunt down the Mesu supply chain to get replacement parts and configuration instructions - great and helpful as those guys may be.

The guiding assistant idea will not work because the drift is not constant, so this will not fix things. I am currently convinced that the clutch design of the Mk2 is faulty and can cause slippage, but this is my layman‘s explanation. I have put far too much work into this and contact with the manufacturer has become more and more unpleasant the more it became clear the mount is the issue. It took three weeks to get him to fix the DEC encoder, and whatever he did in RA (the information oscillates between „nothing“ and torque adjustment) did not address the drift at all. He has now started to claim the first repair was only because of DEC problems while my first mail was titled „Drift in RA“. Extensive testing of the mount after repair is claimed, but no documentation of this is produced even after I repeatedly asked for it. I have contact to several other people with similar experiences. Since this hobby is supposed to be fun I decided to „outsource“ further anger by contracting a lawyer to deal with it.

I use it for an Esprit 100 photographically without any issues, should work well for the 120mm ED for visual. After a belt mod, no problems even at 1500mm FL with an RC8 (0.4”/pixel), guiding at 0.8-.09” RMS. Easy to set up. Only thing that could be said is that the Sky-Watcher hand controller seems a bit 80ies.

Thanks for trying to help, again. Unfortunately this did not turn out well after all. I thought to post here because reports on this forum were instrumental in me deciding for this mount. I got the mount end of September, with „first light“ in Oct 1st. In addition to some problems configuring the Sitech software (which I am now very confident in, it is not so bad once you get to know it), I had the above mentioned troubles with intermittent drift and stopped tracking in RA. The „good hour“ unfortunately was a singular experience. In addition I soon got „Motors in Blinky“ errors in the Sitech software which needed a restart of the mount to resolve. Mr Mesu kept being very responsive but he demanded more and more tests from me. All these seemed to serve the purpose of proving it was not the mount at fault. I lost patience after four weeks and demanded of him to take the mount back for service. I had to pay 140€ of postage to ship back everything except for the counterweight shaft and the bent-knee pier. He diagnosed a faulty DEC encoder which was fixed and adjusted torque on the RA axis. There was a huge stretch of bad weather here for several months which delayed my testing. The “Blinky” problem was solved with replacement of the DEC encoder. Unfortunately the RA drift is still bad (between 2.5-14”/minute). In addition the hand controller causes random slews now. There are other people with similar unresolved issues. Considering the hassle I had before the last repair attempt I asked for return and refund, providing several guiding logs and pictures and doing experiments with two different scope setups. This was denied. Mr Mesu keeps claiming “other equipment” as the possible source of error even though the scopes work on other mounts and no scope/guider works on the Mesu mount. He also claims to have done extensive tests of my mount but will not provide any documentation. This has become a very frustrating experience and has cost me more than 40 of hours of clear sky time. I will now turn this over to a lawyer.

Thanks again for the help, everyone. I have some unexpected clear skies tonight. After upgrading and reinstalling the Sitech software I now have no more tracking issues. Guiding is at 0.35" RMS, which seems excellent with (for here) mediocre seeing of about 2" FWHM, and there is still room for improvement of focus on the OAG.

Thank you, again. On the sitech group, someone had the same problem and fixed it by reinstalling the software. I tried reinstalling before. I have now uninstalled and upgraded to a higher version that I found in that forum. I can no longer reproduce the stop of the RA motor. So, next check will be under the stars. If they ever come out again.

Indoor space where a running mount does not lead to marital arguments is heavily constrained (well... used up...). I might have to disassemble a part of the music studio, which is a hassle to cable up again. The mount/scope lives under a telegizmos 365 cover with dew heater. Everything keeps nice and dry there, always. I actually expected the mount to perform from the set-up and not having to start out with lengthy trouble-shooting. I probably should have known better, in this game. I spent more than 10 hours so far (8h and 2h of clear sky) trying to fix various configuration problems. I find the Sitech software incredibly opaque. Before buying, I thought I understood the software. I do not. At all. Most settings are either not needed for the mount, or do not do what I think they do. There is no online help in the software and the manual is a difficult read. The QuickStart from Lucas Mesu was quick and easy to follow. Just, did not work for me. Currently I am using factory settings from Lucas Mesu, just adjusted the location. He is very helpful and approachable. No luck, though.

Thanks again for helping out. I have balanced with great care. Sitech.exe does not show “pier side”, but I think if there was a problem, slewing would be impaired and tracking in other parts of the sky, too (which works fine). I am quite sure it is a problem with my mount settings. I can hear the RA Motor stop when the problem occurs (a bit difficult because the computer is quite loud, it I am sure). Slewing away from equator makes everything work again. Turning off and on and disconnecting etc. does not. With “non-clear skies” what I really meant was basically continuous rain for the last two weeks. I probably should just move the mount indoors and test there.

Thank you for your quick reply. I have not touched the horizon limits yet, but had cleared the horizon file just to be sure, and the problem remained. I have also contacted Lucas, who gave me some config files. These helped with some slewing/alignment problems I had but did not resolve the tracking issues. I am in touch with him, but wanted to tap into the knowledge of the userbase, too. With the abysmal weather here, the testing proceeds rather sluggishly (2h of clear sky in 2 weeks).

Hello, I am Torben, from Germany. I found quite a few posts here regarding the Mesu mounts, some of which convinced me to purchase one as a step to using larger scopes. Unfortunately, I have a problem with tracking: If I slew to a target near the celestial equator, RA tracking stops after a few seconds. Sitech.exe will report the scope status as tracking and RA/DEC coordinates stay constant. I can only resume tracking by slewing to a different target.I am using Voyager for imaging control, but I could isolate the problem, and it occurs without Voyager, too. Sitech version is 0.94N from the Sitech web site. Does anyone have an idea what the cause could be?