The weight advantage is huge. I own a RST-135E and it's amazing how much more I get out now with the lighter mount. Saying that.... Harmonic drive PE is very different to worm drives. It's always changing based on the weight and angle th mount is at (based on torque on drive in current orientation), so can not use PEC/PPEC like you can with EQ6, etc. This means the true error is MUCH worse than what you may be used to. Not saying it can't be overcome, but don't compare error bars of harmonic drives to more traditional drives.
The biggest thing with these mounts is you need very fast guiding exposures to keep on top of the PE as it can move quite fast at some parts of the sky so you need good SNR for your guide cam so it can keep on top of it.
Thanks for the info.
I think this shows a good gap in the market, that a product like the SkyWatcher AZ-GTi hints towards.
I'd love something a little heavier/beefier than the AZ-GTI but with the accuracy of say the EQ6-R in a package not much bigger than the AZ-GTI. Of course, I'd be willing to sacrifice mount weight capacity, and maybe image with 6-7kg of equipment.
That would drive a perfect travel and wide-field setup
This AM5 ticks a lot of boxes, but it might be exactly what I'm after, personally. We'll see.
So yeah, half the price of the Rainbow Astro (less than half compared to the RA Encoder version)... but still, that's a lot of dollaroos. I'll wait to see if SkyWatcher updates the AZ-GTI.
Well, I put down a $1,000 deposit with Testar for the AM5. Hopefully by the time they arrive there will be some public PHD logs or guiding reviews and I can make a final decision as to whether I should proceed.
I asked Testar a few questions about these mounts - mainly prompted by a very good review on YouTube, and received the answers quoted below. Very helpful people there:
1. The quoted 0.5 to 0.8 arc seconds figure is the typical guided tracking accuracy.
2. There is no ( power failure) brake on the DEC axis (like there is on RA.) According to ZWO this is not necessary, but I have reached out to them for more information.
3. The mount is suitable for long exposures, depending on your focal length, guiding configuration, seeing and environmental conditions, etc. Generally I wouldn’t go longer than 10 minute exposures with mounts in this class. If you need greater accuracy, there is always Avalon or 10 Micron (although of course these are a step up in price).
4. The 900mm figure is based on ZWO’s recommendation to keep your pixel scale above 1 arcsecond/pixel, given the common pixel size of around 4um. Lower than that, and you may hit the limits of the guided tracking performance.
I’m a bit puzzled by item 4. I fail to make the leap from the pixel scale of the imaging camera and guiding performance. Still, I admit to spending a lot of time head-scratching these days.
That guiding accuracy doesn't sound great for the price? No better than my old modded CGEM.
The 900mm'ish focal length makes sense with a standard camera given that guiding accuracy. Its near the arcsec pixel size
Nonetheless, be interesting to see how it performs
Yep, personally I wouldn't get a HD mount (unless it has encoders) for a long FL scope. As such putting the FSQ85ED on my HD mount (where with my camera, it's 1.7"/px - so guiding RMS of 0.5-0.8 is within limits).
I asked Testar a few questions about these mounts - mainly prompted by a very good review on YouTube, and received the answers quoted below. Very helpful people there:
4. The 900mm figure is based on ZWO’s recommendation to keep your pixel scale above 1 arcsecond/pixel, given the common pixel size of around 4um. Lower than that, and you may hit the limits of the guided tracking performance.
I’m a bit puzzled by item 4. I fail to make the leap from the pixel scale of the imaging camera and guiding performance. Still, I admit to spending a lot of time head-scratching these days.
I’m still chewing this over.
I have done nearly all of my imaging on either a TV85 or more recently an Esprit 120. This is more or less my desired image scale and since i don't have a permanent setup really value portability, so the recommended FL is fine for me.
I may even try and trade the Esprit 120 for an Esprit 100 to enhance portability.
If I can get a consistent 0.5 rms then I will be satisfied.
I also have a Edge 9.25 which I use for planetary and here guiding is not an issue, so the mount should be fine for that as well.
Anyone got one of these yet? I'm hoping mine comes in the next couple of weeks. Hoping to hear from people with real world experience. I have heard that the performance is very good, at least for AP.
For visual, apparently anything more than 1 star alignment doesn't work.
An AM5 is high on my list for a number of reasons but mainly the amazingly compact size for its weight capability as a travel grab and go (and I am unashamedly beholden to the programming skills of ZWO and their eco-system, so I know it will perform).
A couple of thoughts based on limited knowledge, so feel free to debate:
Harmonic drives have no backlash, and I mean NO backlash, it's why they are used in robotics. Even the best tuned belt driven mount i've seen has a few arc seconds of give which can cause issues on blustery nights. I'd love to see the imaging/guiding results on far less than perfect nights in the field with this mount.
The ZWO uses stepper motors rather than servos like others. Stepper motors lock without power - it's actually quite hard but not impossible to move them. The break on power failure for the RA drive suggests that 13+ kg without counterweights is sufficient to overcome the natural resistance to movement!
An AM5 is high on my list for a number of reasons but mainly the amazingly compact size for its weight capability as a travel grab and go (and I am unashamedly beholden to the programming skills of ZWO and their eco-system, so I know it will perform).
A couple of thoughts based on limited knowledge, so feel free to debate:
Harmonic drives have no backlash, and I mean NO backlash, it's why they are used in robotics. Even the best tuned belt driven mount i've seen has a few arc seconds of give which can cause issues on blustery nights. I'd love to see the imaging/guiding results on far less than perfect nights in the field with this mount.
The ZWO uses stepper motors rather than servos like others. Stepper motors lock without power - it's actually quite hard but not impossible to move them. The break on power failure for the RA drive suggests that 13+ kg without counterweights is sufficient to overcome the natural resistance to movement!
Looking forward to some real world reviews!
Given the issues I had with my copy of the recent Star Adventurer GTi, I'm also interested in some real world reviews of this.
I don't have a lot of knowledge in relation to the "strain wave" system though. Anybody care to recommend a good article / video on this?
T Harmonic drive PE is very different to worm drives. It's always changing based on the weight and angle th mount is at (based on torque on drive in current orientation), so can not use PEC/PPEC like you can with EQ6, etc. This means the true error is MUCH worse than what you may be used to. Not saying it can't be overcome, but don't compare error bars of harmonic drives to more traditional drives.
The biggest thing with these mounts is you need very fast guiding exposures to keep on top of the PE as it can move quite fast at some parts of the sky so you need good SNR for your guide cam so it can keep on top of it.
This is very interesting, a rare look into actual user feedback.Pretty damning in IMO. On Testars web site "very low periodic errors (within ±20 arc-seconds) make the AM5 an excellent mount for astrophotography". thats a bit of a stretch . A very specific use case, the need for very fast guiding exposures. If this had output encoders, and ZWO could actually get these encoders to work reliably with guiding to get PE (or it seems just high non PE errors) down this would become a killer mount.
The high PE is not really an issue. On Cloudy nights, most users are getting between 0.4-0.6RMS for guiding and good star shapes. There's not much else that matters really. There are occasional spikes, but really the mount seems to be performing very well from what everyone has experienced so far.
My one will be here end of September unfortunately. Still a long wait to get my hands on one.
Had mine a while now, and absolutely love it. So much that my humongous CEM70 is packed away possibly to sell.
Being able to pick it up and move about the property fully loaded is a boon.
Very happy.