RST-135 or RST-135E ?

Topic starter

Aug 31, 2022 · Edited: Aug 31, 2022

Dear fellow astrobin users, I'm considering RST-135 or RST-135E for my mobile rig. I always have to carry my rig into the field and set it up from scratch, so I'm limited in terms of total weight. This will result in a limitation of the heft of the tripod I'm able to use with the mount. Something like a pier is out of question. I will restrict myself to lightweight scopes too, so it's unlikely that something larger than a 4" f7 refractor will ever be on the mount. So I will be restricted to >1 arcsecond image scale. I'm using the mount mainly for astrophotography. Guiding is no issue to me and seeing in my area is usually around the 1.5 arcsecond range so I expect no issues with the short guide pulses required for the RST-135.

Is there a good reason to invest the extra money for the RST-135E under these circumstances? I understand that the RST-135E has less PE in RA but I'm not sure if I can really make use of this to good effect with a portable setup and if it's really relevant if I'm guiding anyway.

I would be pleased to hear your opinion and your reasons why you decided for one or the other as well as your experience with the mount.

Thank you and clear skies
Wolfgang

Engaging

andrea tasselli

Frequent contributor

Sep 1, 2022

Guiding is no issue to me and seeing in my area is usually around the 1.5 arcsecond range so I expect no issues with the short guide pulses required for the RST-135.

Are you living on top of a 4000 meter mountain somewhere on an island surrounded by a vast ocean by any chance? Any chance I can get there too ;) ?

kuechlew

Topic starter

Sep 1, 2022

andrea tasselli:
Guiding is no issue to me and seeing in my area is usually around the 1.5 arcsecond range so I expect no issues with the short guide pulses required for the RST-135.

Are you living on top of a 4000 meter mountain somewhere on an island surrounded by a vast ocean by any chance? Any chance I can get there too ;) ?

South of Germany, you're always welcome to join me in my public place. Maybe I'm missing something but that's what meteoblue seeing forecast tells me:

Sometimes it's a bit better, sometimes a bit worse. I only do this since 1 year but so far I didn't have a session where the meteoblue values were worse than 2 arcsec, so something around 1.5 is fairly normal.

Always happy to learn about possible misconceptions.

Clear skies
Wolfgang

Wei-Hao Wang

Sep 1, 2022

I think the E version is valuable when you image with focal lengths below 300mm or so, where you can completely do away with guiding. If you use a DSLR and find a way to attach an optical polar scope (this is what I am trying at the moment), you can even image without a computer. That's when things become super portable. In my portable imaging, I do enjoy the possibility of not guiding for 100 to 300 mm.

But of course, if you are OK with guiding, with carrying a computer and the require power source, with the very short guide exposure, then the non-E version should be fine for you.

Helpful Insightful Respectful

andrea tasselli

Frequent contributor

Sep 1, 2022

andrea tasselli:
Guiding is no issue to me and seeing in my area is usually around the 1.5 arcsecond range so I expect no issues with the short guide pulses required for the RST-135.

Are you living on top of a 4000 meter mountain somewhere on an island surrounded by a vast ocean by any chance? Any chance I can get there too ;) ?

South of Germany, you're always welcome to join me in my public place. Maybe I'm missing something but that's what meteoblue seeing forecast tells me:

Sometimes it's a bit better, sometimes a bit worse. I only do this since 1 year but so far I didn't have a session where the meteoblue values were worse than 2 arcsec, so something around 1.5 is fairly normal.

Always happy to learn about possible misconceptions.

Clear skies
Wolfgang

Ah, THAT! Ok, I was thinking of something real. Like actual 1.5" seeing on average at the business end of a telescope all year long. THAT would be something to behold!

Wei-Hao Wang

Sep 1, 2022

Meteoblue forecast constantly says my site has 0.3 to 0.5 arcsec of seeing, all the time. And in reality my typical seeing is 1.4 to 2.0 arcsec.

So I wonder what the real seeing would be when meteoblue says 1.5 arcsec.

Well Written Engaging

andrea tasselli

Frequent contributor

Sep 1, 2022

Wei-Hao Wang:
Meteoblue forecast constantly says my site has 0.3 to 0.5 arcsec of seeing, all the time. And in reality my typical seeing is 1.4 to 2.0 arcsec.

So I wonder what the real seeing would be when meteoblue says 1.5 arcsec.

Easy enough: much worse!

kuechlew

Topic starter

Sep 1, 2022

Thank you for pointing this out. While it's not the topic of the thread, do you know any reliable source of seeing conditions?

Clear skies
Wolfgang

Well Written Respectful

andrea tasselli

Frequent contributor

Sep 1, 2022

None other than yourself. If you have the right gear for a quantitative analysis.

More on topic, why this thing with harmonic drives? Wouldn't a normal GEM do, given that they come quite light nowdays? Or what about this:

https://www.avalon-instruments.com/products-menu/mounts/evo-zero-detail

kuechlew

Topic starter

Sep 1, 2022

andrea tasselli:
None other than yourself. If you have the right gear for a quantitative analysis.

More on topic, why this thing with harmonic drives? Wouldn't a normal GEM do, given that they come quite light nowdays? Or what about this:

https://www.avalon-instruments.com/products-menu/mounts/evo-zero-detail

As usual your advice is much appreciated Andrea. Could you please point me to some source on how to perform such an analysis?

I really have to carry my equipment in a backpack therefore even "lightweight" GEMs get quite uncomfortable. I considered some lightweight GEMs like the Vixen SXD2, iOptron CEM 26, Explore Scientific EXOS-2 PMC-8 or Celestron AVX but including the corresponding tripod and counterweights you'll always end up with significantly more than 10 kg.

Since I want to buy a future proof mount I have to take into consideration that I won't get younger and stronger. With my current physical condition it wouldn't matter too much to lug 30 kg into the field. Approaching 60 I may think differently in 10 years from now. In addition to the weight the bulk of conventional mounts becomes an issue too. I neither want to look nor feel like a mule ...
My excursions into astrophotography look a bit like this: (1) Astrophotography Japan /Touching the Planets (Episode 6) - YouTube at 15:37.
No, that's not me but I'm really working similarly hard for my data ...

If I had a backyard I would not care the least about harmonic drives and just order one of these wonderful large and heavy GEM mounts with their meticulous accuracy. I just have to live up to the reality though. It's all about pursuing this hobby at all under the given limitations.

The Avalon mounts seem to have a good reputation and the evo zero is on my shortlist - as is the predecessor M-zero. The only issue I have is that the Avalon mounts seem to be a niche product with a quite limited user base. Not sure if this is a good choice for a still inexperienced astrophotographer. The Evo Zero is very new and I could not find any user reports whatsoever in the internet. Maybe that's a good thing and the owners just happily snap their astroimages. However there are no astrobin entries either so far. The M-zero seems to be reliable except for occasional belt issues but is a bit bulky compared to the Evo Zero and RST-135.

As I wrote in another thread I will not buy the mount before second quarter of next year so I'm open to further information and may revise my current assessment at any time. At the moment the RST-135 (with or without E) is my top pick with the Evo Zero / M-Zero, the upcoming Pegasus Nyx and the ZWO AM5 still "under observation" on my short list.

I'm not too enthusiastic about the harmonic drive technology but I trust into its longevity and given my use case I believe it fits the bill. The drawbacks in terms of large, irregular PE and short-term spikes in RA and Dec movement should not be too significant for my image scale and level of ambition. As I said I'm always open to learn otherwise.

Thank you for your support and clear skies
Wolfgang

Respectful Supportive

Stefan

Sep 1, 2022

I have the RST-135E and it's a great mount.

With accurate polar alignment and levelling it doesn't need guiding.

Guiding is a pain and if you're at any decent FL you'll need a good guidescope and guidecam to be able to get enough stars for the fast guiding exposures. I don't guide with mine and it can do 5 minute subs easy at 414mm. It'll save you some kg of carry by not guiding too.

Helpful Concise

andrea tasselli

Frequent contributor

Sep 1, 2022

As usual your advice is much appreciated Andrea. Could you please point me to some source on how to perform such an analysis?

I really have to carry my equipment in a backpack therefore even "lightweight" GEMs get quite uncomfortable. I considered some lightweight GEMs like the Vixen SXD2, iOptron CEM 26, Explore Scientific EXOS-2 PMC-8 or Celestron AVX but including the corresponding tripod and counterweights you'll always end up with significantly more than 10 kg.

Since I want to buy a future proof mount I have to take into consideration that I won't get younger and stronger. With my current physical condition it wouldn't matter too much to lug 30 kg into the field. Approaching 60 I may think differently in 10 years from now. In addition to the weight the bulk of conventional mounts becomes an issue too. I neither want to look nor feel like a mule ...
My excursions into astrophotography look a bit like this: (1) Astrophotography Japan /Touching the Planets (Episode 6) - YouTube at 15:37.
No, that's not me but I'm really working similarly hard for my data ...

If I had a backyard I would not care the least about harmonic drives and just order one of these wonderful large and heavy GEM mounts with their meticulous accuracy. I just have to live up to the reality though. It's all about pursuing this hobby at all under the given limitations.

The Avalon mounts seem to have a good reputation and the evo zero is on my shortlist - as is the predecessor M-zero. The only issue I have is that the Avalon mounts seem to be a niche product with a quite limited user base. Not sure if this is a good choice for a still inexperienced astrophotographer. The Evo Zero is very new and I could not find any user reports whatsoever in the internet. Maybe that's a good thing and the owners just happily snap their astroimages. However there are no astrobin entries either so far. The M-zero seems to be reliable except for occasional belt issues but is a bit bulky compared to the Evo Zero and RST-135.

As I wrote in another thread I will not buy the mount before second quarter of next year so I'm open to further information and may revise my current assessment at any time. At the moment the RST-135 (with or without E) is my top pick with the Evo Zero / M-Zero, the upcoming Pegasus Nyx and the ZWO AM5 still "under observation" on my short list.

I'm not too enthusiastic about the harmonic drive technology but I trust into its longevity and given my use case I believe it fits the bill. The drawbacks in terms of large, irregular PE and short-term spikes in RA and Dec movement should not be too significant for my image scale and level of ambition. As I said I'm always open to learn otherwise.

Thank you for your support and clear skies
Wolfgang

Here you go:

https://www.alcor-system.com/new/SW/DIMM_Software_Manual.html

You can get the basic math from the linked papers.

Or you can measure the fwhm on short exposures (<1s) and created your moving averages seeing estimates.

Good luck for your choice of portable set-up. Not easy but I can understand your concerns although I'm used to lug stuff anyway and carryng a GP/DX never was a problem for me (I'm 60-ish too). As for the Avalon I expect there wlll be soon someone biting the bullet and getting one. They have a rather large user base but I expect the most won't bother publishing results except maybe in italian astro forums.

To be honest the thing I hate most carry around is the tripod and there is no way around it, it is got to be bulky to be stable.

Would you choose an RST-135 or RST-135E under the given circumstances?