Kevin_A Is it [worth] going to the 135E instead?

It all depends.

The Renishaw encoder in the 135E is only good to 2.5". So, if your plate scales need better than that (or you have nights where the "seeing" is better than about 2"), then the encoder will do you no good.

Think of it this way: gears are not precise enough for an arcsecond type precision. There are two ways to solve this -- one is to use the reference from a very precise encoder, and the other is to use the star themselves as even more precise reference points. Autoguiding is pretty much just using the stars as a very precise encoder (as long as the mount does not have glitches and respond properly to feedback pulses). In both cases, you establish a feedback loop to get the motors to point correctly again -- this is also why I prefer mounts that use servo motors instead of the (much) cheaper stepper motors that Chinese mounts (not just ZWO) use.

If you need better than 2.5" tracking, then you still need to autoguide anyway, and an encoder is wasted.

The reason I went from my initial two RST-135 to an RST-135E is that for a lot of my usage does not require high precision tracking (short focal length, planetary, solar [with FOA-60Q and a pair of Lunt filters [really heavy when double stacked!]).

I was so happy with the 135E (the peak error is 2.5", so the RMS error is more like 1.8") that I bought a second one, so that is how I eneded up with my current four RainbowAstro mounts.

My largest DSO scope only has 450mm focal length, so I can pretty much live with just the encoder alone. For planetary, you simply need to make sure the planet does not move out of the ROI. Ditto Solar.

So, for me at least, the 135E is definitely worth the upgrade from the 135 (you only live once, especially with the weather) -- wouldn't you pay an extra $200 to get rid of clouds just for one night? Fighting autoguiding error is just penny wise, pound foolish.

As to autoguiding, using 2 FPS guide camera,using the parameters that I had discussed here before (max step of less than 100, aggressiveness of less than 25%, overexpose by 10 dB over 12 stars), and a decent guide scope (either the 55mm BORG flourite, or the Vixen 55mm flourite), I can get a stable 0.25-0.35" total RMS tracking error (assuming calm winds) from the non-E. But you need to add the weight of a good guide scope, etc. Just like I was tired of counterweights and balancing, I also got tired of autoguiding.

Cheap mount + cheap guide scope is asking for trouble. If you cannot get a flat field, avoid using multi-star guiding.

On top of that, too many people try to autoguide away errors that are not caused by the mount (like wind), and end up with wild long term errors -- I simply don't understand why people have so much progblem autoguiding -- such people should just get a mount with an encoder. Autoguiding, like encoders, are to reduce mount errors, not wind, not field rotation. Stop tweaking the parameters to get short term error down (for the next 30 seconds). Compute what is needed, and use that setting for long term guiding.

ASIAIR also has a multi-star centroid problem, so you need to avoid using ASIAIR unless you restart autoguiding once every 30 minutes or so.

Chen

eyecon I saw that the rst uses servos rather than steppers so that to me indicated a general approach based higher end components.

My 20+ year old EM-11 mount uses servos. Of couse, Takahashi machining is smooth as silk. Steppers should be banned from being used in mounts.

I just don't enjoy balancing things every evening so it is not in use anymore.

Chen

w7ay I have come to the conclusion that with asiair and the zwo mount that no matter what you do in regards to duration and aggression and other setting changes, the inferior choppy PE in some mounts cannot be tamed consistantly or reliably especially by the whacky phd2 implimentation in asiair. It is best to say it is possible to get 0.5 but some of the time all hell brakes loose randomly anyways where the bad machining is evident. I will apply what I have learned one day to a better mount. I agree the rst135e is probably best for visual or when guiding is not required.

Kevin_A is there much difference between RST and Crux mounts?

The Crux are made by HOBYM (also Korean).

Many years ago, RainbowRobotics's founder had partnered with HOBYM's founder to produce what I believe were the first mounts that are based on Harmonic Drives. This was when the gears are almost double the price of today's gears from Harmonic Drive [tm].

RainbowRobotics's founder left the partnership, and eventually produce the RST-150h ("h" for harmonic) from the RainbowAstro that he'd spun off RainbowRobotics. It was about $7000, if memory serves, and I was at one point deciding between buying it or the Avalon M-zero (I really like the no-meridian-flip single arm fork).

After a year of indecision on my part, RainbowAstro introduced the RST-135 after Harmonic Drive [tm] released a lower priced gear (announced late 2019), and allowed the RST-135 to come in below $4000. That became a no-brainer for me, and I ordered an RST-135 sight unseen. My first RST-135 came from the first production run, with serial number A013. (My newest RST-135E has serial number E319.)

There are two reasons why I went to the RainbowAstro instead of the HOBYM. Notice that HOBYM always has that external dangling wire that is present also in the small Crux' design, and more importantly, the RainbowAstro has a really clean communications protocol (literally three short PDF pages), which is widely supported (INDIGO, ASIAIR, etc). RainbowAstro also has a Cloudy Nights presence (xuranus, who is B. J. Leong, an R&D manager for both RainbowAstro and RainbowRobotics) -- I usually get an email reply within a day after writing to him. And with real technical answers, instead of "try a different cable."

Engineering documentation appears more complete from RainbowAstro, too. When you write your own software, being able to find documentation is essential.

Crux does come in more models with different payload limits. RainbowAstro is either 13.5 kg or 30 kg. The smallest Crux is quite tempting as a small portable mount.

If you search long enough, you can also find a Japanese boutique company who produces the SS-One mount, also using real Harmonic Drives. But they probably sold only single digits, or at most a couple of dozen of them.

https://www.iceinspace.com.au/forum/showthread.php?t=173643

Chen

Kevin_A

BTW Kevin, this is one of the larger mounts by RainbowAstro:

https://www.rainbowastro.com/ko/rst-2000f/

They used to also sell an RST-400; but it (and the above) may only be for the Korea market.

https://www.rainbowastro.com/ko/rst-400/

BTW, the sky was partially clear last night (and not freezing) for the first time in months, so I decided to try out the Beta ASIAIR. After months of sitting outside (Mortar tri-pier, RST-135E, electronics box with ASIAIR, etc) in the rain and snow (under two layers of dry bags :-), the semi-permanent (pretty much permanent, since I leave everything outdoors) setup's polar alignment was off by less than 20 arc seconds. This is how the two RST-135E is being used right now. The small portable guy with the Vixen OTA (237mm focal length f/4.3) is on a Takahashi metal tripod -- the legs are spread out as far as the Mortar's legs:

Sky completely clouded over by 1 am. This is Portland :-).

BTW, the RST-135E unguided is not good enough for DSO on the FSQ85 at 455 mm focal length. You can easily see elongation of stars. But it should be OK unguided by 135mm or shorter focal lengths (I have the Sigma 135 and Sigma 50 ARTs for that). Oh, the guide scope in the picture is an FMA180-p (with ASI178MM). You can see 3 EAFs in this picture -- between my different OTAs, I think my stockpile has now over 10 EAFs.

Chen