GTD - Gemini vs MESU 200e vs Fast linear buying advice?

[Gorr_77]

Hi All,

I am following this forum for a decade now and feel like I personally know some of the users and recognise their names, after reading so many great topics.

I would like to ask whoever like to share,for an advice on the purchase i am about to made - a new mount! or BIGGER mount...

Currently i have MZero and is great! but not strong enough to accommodate more weight, so i will have to sell it soon - i've almost got used Avalon linear  - no service and low PE readings - for me low PE is on top of the pyramid:)- but recently i acquired small triplet for fraction of the price and the whole new idea opened up.

I'm so PRO with friction tech and I am thinking of Mesu 200e - or maybe 200??? or new GTD? - price between 2k - 6k, waiting time -  both confirmed 6-8 weeks delivery.

Everyone talks about MESU being so reliable.. check this clip for new GTD tracking:

I am setting up 23-26kg gear - 2x80mm triplets, with ccds and filter wheel - on a tripod!! (something to think about) - GTD and MESU will take that ..Avalon Linear probably not.

I do understand that they are very low on tracking error, and all kinda portable - so it suits me, i will have to take it out every night.

I could set myself on used G53F of MESU 200.... - or ,is it worth to stretch  for the new ones? add encoders - or not? what controller would you use?

The list is long and it won't happen quick....As you know there are so many questions.

Far east market?  - i.e. IOptron with new CEM70?... or maybe others? 

I really don't mind any controller as to me they all do work.... sometimes with a lot of patience

So please, if you have any thoughts, good or bad experience and dont mind to share it would be very much appreciated.

Kindest Regards

Greg

 

 

[JamesF]

Given your payload you're possibly asking too much of a CEM70 assuming they expect it to have a maximum payload of 70lbs and from what many people say about keeping an imaging payload to about two thirds of that.  The CEM120 would presumably manage it easily though.

James

[vlaiv]

Here is a thought.

How about Berlebach planet tripod + CEM120.

If you guide - get non EC version. If you don't guide get encoders.

Mind the weight of the thing - 25+Kg!

 

[Gorr_77]

Hi James,

I was aiming for CEM120 mount for few years as i ve used CEM60 for few years but .... i am not so sure if Ioptron is keeping it for long, few guys here and there talking about design change etc.... i really thought that everyone will come up on NEAF with updates.... but as per usual - no! 

Going back to GTD - it has same price - but is brand new...

 

[Gorr_77]

Hi Vlaiv

Beautiful!! Beast....

Guiding is seeing - is that right?

I will guide it through.... no EC 

I had wooden tripod - and wasnt very stable - in my understanding.....

But all possible...... 

[vlaiv]

1 minute ago, Gorr_77 said:

Guiding is seeing - is that right?

Guiding - using a small telescope / finder / guider scope or OAG (off axis guider device) to monitor position of the star and issue corrections to mount tracking if reference star deviates from expected position.

Many mounts suffer periodic error - mount has a period (associated with reduction gear) and inside that period - it does not always track perfectly - sometimes it lags and sometimes it is in front of where it ought to be. This is because gear train elements are not perfectly round (just mechanical thing - you can't make something perfectly smooth or round or whatever - only to certain precision).

This leads to elongated stars more often than polar alignment error. Guiding solves both - periodic error and polar alignment error - and couple more things, but requires special gear to be used - guide scope or OAG, guide camera and computer.

Encoders deal with periodic error and make motion of mount very precise - so you don't need to guide to correct periodic error, but you still have polar alignment error to worry about and some other things (that are usually not much of an issue - like apparent star positions due to atmospheric refraction and such).

[Gorr_77]

you see i am thinking to go with a scope instead of OAG on the 80mm, but i will keep it for the c11... most of the times if the mount (Mzero cant keep up 8-10min) for me is too (i.e.)hectic /cloudy.. so the mounts mentioned should be good - without encoders - i don't mind to loos night or two on a larger scale....:)  

What do you think?

[Gorr_77]

Well,

If your Polar alignment is perfect and the setup has no flex, think that the idea to run a session without encoders and guiding on 1000mm, achieving 0.5PE , is something that many AP wants, without paying a lot of hard saved cash.

[Gorr_77]

hey!

Just Found another bit to the puzzle :

Gemini guiding:

So three on the list: for me:

- Mesu 200e

- JWT Trident

-Gemini E. Fric

Ive took the Avalon  Linar off the list as it has fallen in another class...

[Jkulin]

On 24/04/2020 at 23:06, vlaiv said:

f you guide - get non EC version. If you don't guide get encoders.

Hi Vlaiv, I have the 120EC with just the encoders on the RA and personally although it is producing some excellent results, I do not believe that it performs unguided.

Don't get me wrong for the money it is hard to beat and with my Bortle 5 skies as long as I get round stars then I don't care, I always use an OAG and when I finally switch over to my Esprit 80 and 100 they will run with an OAG.

I have found that using a guide scope combination gives false readings and will make your guiding look better than it actually is.

For me I want to know precisely how bad or how good it is performing.

I am far from the technical mind that you have, but results speak for themselves.

I was capturing some really tricky targets with gusts of up to 28mph and the 120EC gave me reasonable results where I am sure that a guide scope would have failed and that was at 2007mm FL.

Had I wanted to spend a few grand more and had a permanent observatory then the Mesu would have been my first choice, but because I put two covers over my scopes at the end of each session I always have to redo the polar alignment prior to commencing a session and I believe that to get the best out of the Mesu you should really drift align, something which I do not have time for with our skies.

Now if I really had the money then a GM2000 would be my choice or if I could find one an ASA85 with the absolute encoders, however the Rainbow mounts look very interesting and over the next couple of years I will be watching them very closely.

Edited April 29, 2020 by Jkulin
typos

[RayD]

I have a Mesu 200 and a CEM120 EC.  CEM is excellent, but the Mesu takes it due to the 100% friction drive and 100Kg payload.  Exceptional mount within its price range, in my opinion.

[RayD]

36 minutes ago, Jkulin said:

Hi Vlaiv, I have the 120EC with just the encoders on the RA and personally although it is producing some excellent results, I do not believe that it performs unguided.

Don't get me wrong for the money it is hard to beat and with my Bortle 5 skies as long as I get round stars then I don't care, I always use an OAG and when I finally switch over to my Esprit 80 and 100 they will run with an OAG.

I have found that using a guide scope combination gives false readings and will make your guiding look better than it actually is.

For me I want to know precisely how bad or how good it is performing.

I am far from the technical mind that you have, but results speak for themselves.

I was capturing some really tricky targets with gusts of up to 28mph and the 120EC gave me reasonable results where I am sure that a guide scope would have failed and that was at 2007mm FL.

Had I wanted to spend a few grand more and had a permanent observatory then the Mesu would have been my first choice, but because I put two covers over my scopes at the end of each session I always have to redo the polar alignment prior to commencing a session and I believe that to get the best out of the Mesu you should really drift align, something which I do not have time for with our skies.

Now if I really had the money then a GM2000 would be my choice or if I could find one an ASA85 with the absolute encoders, however the Rainbow mounts look very interesting and over the next couple of years I will be watching them very closely.

I don't think iOptron ever intended for this to be used unguided, John.  I think the encoders are designed simply to reduce the PE to a very low level which makes the guiding much easier with less corrections needed.

I love mine and really enjoy using it when I get chance!

[Jkulin]

Just now, RayD said:

I don't think iOptron ever intended for this to be used unguided, John.  I think the encoders are designed simply to reduce the PE to a very low level which makes the guiding much easier with less corrections needed.

I love mine and really enjoy using it when I get chance!

Yep I believe you are right Ray, I have seen it quoted that you can get 30 min exposures unguided with it, I seriously doubt that they are looking at things closely enough.

BTW did you upgrade the FW I sent you and if so, did you notice the improvement?

[RayD]

Just now, Jkulin said:

Yep I believe you are right Ray, I have seen it quoted that you can get 30 min exposures unguided with it, I seriously doubt that they are looking at things closely enough.

BTW did you upgrade the FW I sent you and if so, did you notice the improvement?

Yeah I'm not convinced half hour unguided is realistic, personally.  However, with the very low PE I've found guiding very easy indeed.

No I've not tried it yet.  We were due to go to Spain but things obviously changed somewhat for a couple of reasons.  I will be going as soon as I am possibly able and will load the firmware then and try it.  Unfortunately it isn't something I can do remotely, as you know 😐

[Jkulin]

Just now, RayD said:

We were due to go to Spain but things obviously changed somewhat for a couple of reasons.

Hope everything is working out OK Ray.

ATB

[Northernlight]

I think the old rule applies - get the best you can afford. Of the mounts you listed I would get the mesu if I had the money.

 

[vlaiv]

10 hours ago, Jkulin said:

Hi Vlaiv, I have the 120EC with just the encoders on the RA and personally although it is producing some excellent results, I do not believe that it performs unguided.

Not sure if you understood me properly.

I was simply implying that if OP does not want to guide - mount with encoders will provide better results than one without encoders.

If OP wants to guide (and that is only sensible option to me), then I simply said that encoders are too expensive and not needed in that case. I might be wrong though. Do you find EC version of mount better performing when you guide?

[Skipper Billy]

If you planning to set up and break down every session juts be aware that the Mesu is heavy.  With the c/wshaft and cw weights mine is approaching 45kgs. 

 

[Zakalwe]

Don't get hung up on low PE and encoders would be my advice.
PE is fine as long as it's low and slow. Guiding will cope with that with very few issues.

Ditto for encoders. You can plate-solve within seconds now, so a super-duper sky model is a bit redundant. Who cares if the mount hasn't the foggiest clue where it is when you can just point it skywards and have an accurate solve & sync done in 30 seconds? Encoders come with their own problems too...the setup needs to be very, very stiff. Yes, with a good setup you can do unguided imaging, but to be honest, guiding is not that difficult and it pretty much just works.

You'd be fine with a Mesu, though less so if yo are setting up each night. It's a heavy lump of a thing. The newer version can be broken down, but get in the gym if you want to be humping it about the place.

[andrew s]

On 27/04/2020 at 15:50, Gorr_77 said:

Well,

If your Polar alignment is perfect and the setup has no flex, think that the idea to run a session without encoders and guiding on 1000mm, achieving 0.5PE , is something that many AP wants, without paying a lot of hard saved cash.

There is no such thing as perfect polar alignment. The position of the refracted pole varies with where you are pointing in the sky. Without some form of model to compensate for this you will get drift.

The best you can do is aim for the mean refracted pole. 

Regards Andrew 

[Zakalwe]

15 hours ago, Gorr_77 said:

hey!

Just Found another bit to the puzzle :

Gemini guiding:

So three on the list: for me:

- Mesu 200e

- JWT Trident

-Gemini E. Fric

Ive took the Avalon  Linar off the list as it has fallen in another class...

Personally, I'd take the JTW vapourware off the list.

 

[DaveS]

16 minutes ago, Zakalwe said:

Don't get hung up on low PE and encoders would be my advice.
PE is fine as long as it's low and slow. Guiding will cope with that with very few issues.

Ditto for encoders. You can plate-solve within seconds now, so a super-duper sky model is a bit redundant. Who cares if the mount hasn't the foggiest clue where it is when you can just point it skywards and have an accurate solve & sync done in 30 seconds? Encoders come with their own problems too...the setup needs to be very, very stiff. Yes, with a good setup you can do unguided imaging, but to be honest, guiding is not that difficult and it pretty much just works.

You'd be fine with a Mesu, though less so if yo are setting up each night. It's a heavy lump of a thing. The newer version can be broken down, but get in the gym if you want to be humping it about the place.

I use an ASA DDM60 and am in the process of commissioning an ASA DDM85, and would never willingly go back to any form of guiding. In fact, to get either mount off me it would have to be prised from my cold dead hands.

[newbie alert]

16 hours ago, Gorr_77 said:

hey!

Just Found another bit to the puzzle :

Gemini guiding:

So three on the list: for me:

- Mesu 200e

- JWT Trident

-Gemini E. Fric

Ive took the Avalon  Linar off the list as it has fallen in another class...

It's worth noting that the rms figure above are in pixels, not arc sec.. so a like for like comparison should be done at the same scale... brilliant guiding, no disputing that at all..

[Zakalwe]

18 minutes ago, DaveS said:

I use an ASA DDM60 and am in the process of commissioning an ASA DDM85, and would never willingly go back to any form of guiding. In fact, to get either mount off me it would have to be prised from my cold dead hands.

The DDM85 is a £12k mount. For that I'd expect it to wake me in the morning with a cup of tea and a cooked breakfast! 😄

Edited April 30, 2020 by Zakalwe

[Gorr_77]

13 hours ago, RayD said:

I don't think iOptron ever intended for this to be used unguided"...

Defo- and only from commercial point of view it is not possible to adjust production line and get to the mentioned precision, within price buget - i am sure they can, but it would be very marginal market. I wouldn't mind to see " a special edition" mount:  CEM 120 SLR  - let say, same how AMG is working with Merc...