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

[Gorr_77]

Hi Rich,

Thank you.

Weight is a thing - i am hoping to lighten it all - carbon etc... - focuser.... it will get me close to about 27-28kg...

I Am trying to complicate it a bit - and go for SiTech with E.fric .

SiTech has a good development...many users (in here as well) but saying that i don't know one step so ... i will keep quiet for now....

 

[Northernlight]

Just now, Gorr_77 said:

Hmm - i couldn't see on their website... Looks good !! i will open new post..

Thanks

Email Adres at Gemini. He responded to me super quickly within an an hour or 2.  The price delivered to Europe is 3600 euros, the 2,995 price is for outside of europe.  I was told that a ready made compatible controller was 180 Euros.  

I would love to buy the E.Fric and sell my EQ8, but the payload is just too small at 25kg, unless i changed my plans from a 12" newt down to a 10" newt to get the weight down.

 

 

[Gorr_77]

Andras is a great man. 

What I know: it is open source mount - so any /many controllers will do, also the E.Fric can track in open loop (same as 10 micron? i think), so both are limited by Polar A and OTA flectures.

MESU....known SiTech and Encoders (plus encoders upgrade if required).

 

[RayD]

1 hour ago, Gorr_77 said:

Andras is a great man. 

What I know: it is open source mount - so any /many controllers will do, also the E.Fric can track in open loop (same as 10 micron? i think), so both are limited by Polar A and OTA flectures.

MESU....known SiTech and Encoders (plus encoders upgrade if required).

 

10Micron doesn't really track open loop.  It uses a pointing model which accounts for PA discrepancy and any cone error you may have.  It doesn't need guiding but the pointing model is their alternative to it, but the pointing model kind of close loops things.

Edited April 30, 2020 by RayD

[Gorr_77]

Thanks RayD,

SO -  they are using their own model or borrowed from other database? and it will move to the numbers saved within. Got it.

[RayD]

4 minutes ago, Gorr_77 said:

Thanks RayD,

SO -  they are using their own model or borrowed from other database? and it will move to the numbers saved within. Got it.

Yes it is their own internal database which is used to form an accurate pointing model.  @Davey-T has one, and they are one wicked looking mount.

[Jkulin]

12 hours ago, vlaiv said:

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?

 

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

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

Hi Vlaiv, indeed I do understand, but what I am saying is that you cannot use any version of the iOptron 120 without guiding, it is essential, my mount even with an encoder on the RA cannot tracking a perfect sidereal rate without guiding, unlike an ASA or 10 Micron, I'm not sure about the Mesu.

Edited April 30, 2020 by Jkulin

[Gorr_77]

In this money i will have obsy for sure - But it will have to be hPS 2 GM 2000,. Also, -  their attitude is crap - they are even asking to pay for better delivery!!! F***** joke?

In this price range - one day - so many other - ModFod on my def list.....

[Gorr_77]

Juklin

cos Asa, Gemini, Mesu . 10micron and Planewave operate on the model - i optron isn't.

RayD,

You have both - is that right?

[RayD]

25 minutes ago, Gorr_77 said:

Juklin

cos Asa, Gemini, Mesu . 10micron and Planewave operate on the model - i optron isn't.

RayD,

You have both - is that right?

Yes I have a CEM 120EC and Mesu 200.  Neither is necessarily designed for unguided imaging as neither has an alternative option for PA error, atmospheric distortions or cone error, as do the mounts with a pointing model.  However, I have run 15 minute unguided test images just for fun on my Mesu with great success, but I do guide.

Both are excellent and both guide to 0.3"/p regularly.  I'd recommend either but the Mesu, in my opinion, is the better of the 2.

[Gorr_77]

....and more about IOptron i would go with "Rainer" in here:

https://groups.io/

[vlaiv]

45 minutes ago, Jkulin said:

Hi Vlaiv, indeed I do understand, but what I am saying is that you cannot use any version of the iOptron 120 without guiding, it is essentially, my mount even with an encoder on the RA cannot tracking a perfect sidereal rate without guiding, unlike an ASA or 10 Micron, I'm not sure about the Mesu.

Why would anyone pay a thousand extra for encoders that don't work?

[Gorr_77]

Vlaiv,

Cos the company like Ioptron should overcome initial issues and you'd hope that update will solve it - usually that how it is works with any product on any market. But as someone have mentioned: they bit too much  - and they are choking now and cannot swallow.... shame.

I wonder if 3rd party will change that.

[RayD]

11 minutes ago, vlaiv said:

Why would anyone pay a thousand extra for encoders that don't work?

The encoder on the EC model is on the RA axis to reduce the PE to a very low level making guiding very easy.  What happens to the dec axis if you don't guide?

[vlaiv]

2 minutes ago, RayD said:

The encoder on the EC model is on the RA axis to reduce the PE to a very low level making guiding very easy.  What happens to the dec axis if you don't guide?

These are screen shots from iOptron website.

This would imply that one should have less than 0.15" RMS periodic error over 240s.

According to this:

http://celestialwonders.com/tools/driftRateCalc.html

2 arc minutes of Polar alignment error in worse case scenario (largest drift) - gives about 0.5"/minute of drift.

Most people that don't guide, image at shorter focal lengths and resolutions around 2-3"/px. That gives you 4 minutes of drift before Polar alignment error moves you single pixel.

According to specs, you should be able to do easily a few minutes unguided, and even 5minutes and more if you do your polar alignment right (not sure what sort of precision can you get with SharpCap polar alignment routine for example)?

[RayD]

53 minutes ago, vlaiv said:

These are screen shots from iOptron website.

This would imply that one should have less than 0.15" RMS periodic error over 240s.

According to this:

http://celestialwonders.com/tools/driftRateCalc.html

2 arc minutes of Polar alignment error in worse case scenario (largest drift) - gives about 0.5"/minute of drift.

Most people that don't guide, image at shorter focal lengths and resolutions around 2-3"/px. That gives you 4 minutes of drift before Polar alignment error moves you single pixel.

According to specs, you should be able to do easily a few minutes unguided, and even 5minutes and more if you do your polar alignment right (not sure what sort of precision can you get with SharpCap polar alignment routine for example)?

Agreed.  But I do 20 minute subs so how does that help me?

As you rightly show, the EC model with the encoder on the RA axis has an extremely low PE which means there is very little interaction with the guide system, but it is needed.  It just means the guiding is incredibly smooth and accurate for a mount of this price.  The EC2 model has an encoder on the dec axis also but as you rightly pointed out earlier, this axis moves very little, so there is already little for the guider to do anyway, so I did not see this as a necessary addition.

I'm not sure what market iOptron were aiming at with the EC2, but for sure the EC performs exceptionally well with the RA encoder reducing the PE to the level it is at.

As I noted, I have managed acceptable 15 minute unguided subs with my Mesu200, but I still guide with that as well.

I think iOptron have done it smart making it optional to have none, one or two encoders.  If you image wide field and only short subs then the likelihood is the EC will be absolutely fine and perform perfectly well. If you image loger focal length and much longer subs you may want to consider the EC.  I'm not sure where the EC2 fits in, but it is an option if it is felt to be necessary.

It's a good mount for the money, encoders or not.

Edited April 30, 2020 by RayD

[Jkulin]

1 hour ago, Gorr_77 said:

....and more about IOptron i would go with "Rainer" in here:

https://groups.io/

With the greatest respect to Rainer, he lives in a country where the dealer cannot offer proper customer service, any person would have sent it back at the first hint of a major problem, unfortunately Rainer chose not to and the issue has become quite heightened.

I purchased my three iOptrons from Altair Astro and have had nothing but absolutely perfect service from Ian and iOptron as indeed many people that I know. If you have a good dealer which it would appear Rainer has not then it makes things so much easier.

Indeed there have been a couple of issues and they have been sorted speedily and at no cost to me.

I think with Rainer and iOptron it has become a war of Attrition, where the more that Rainer wants the less that iOptron can give and the battle is now war!

Edited April 30, 2020 by Jkulin

[Jkulin]

57 minutes ago, Gorr_77 said:

Vlaiv,

Cos the company like Ioptron should overcome initial issues and you'd hope that update will solve it - usually that how it is works with any product on any market. But as someone have mentioned: they bit too much  - and they are choking now and cannot swallow.... shame.

I wonder if 3rd party will change that.

Unless you have owned an iOptron then this is hearsay.

[andrew s]

Maybe the Dec axis encoder on the EC2 is about removing  backlash when it does have to move.

Regards Andrew 

[RayD]

1 minute ago, andrew s said:

Maybe the Dec axis encoder on the EC2 is about removing  backlash when it does have to move.

Regards Andrew 

Possibly, Andrew.  When looking at the guide graph it really doesn't do an awful lot but if imaging at very long FL I suspect you could well be right, and it would then make sense to have it.

[Jkulin]

@vlaiv

In my opinion it is not just down to specifications it is down to performance, one buys on the specification and expects a certain level of achievement, at just over £4K I knew that I would not be able to achieve any image unguided as the iOptron is not marketed in that way. I would be fairly comfortable imaging guided at 30 or even 40 minute subs and still produce good star shapes.

Through last winter I imaged mostly at 20 minute subs in Bortle 5 skies with an SQM of 19.51 I experienced good guiding (it can always be better) but there was no way with a focal length of 2007mm that I could have achieved anything resembling an image unguided.

The EC encoders on the RA help guiding immensely, but they were never designed to replace the need for guiding.

In my experience with any sophisticated equipment the 80/20 rule comes into play, in the main most can achieve 80% out of their equipment but it takes a lot extra to get the remaining 20%.

@andrew s The 120EC/EC2 does not suffer from any discernable backlash, indeed when I run PHD2 it does not report any measurable, it was one of the main selling points.

Edited April 30, 2020 by Jkulin

[andrew s]

I have a Paramount ME II with a OO ODK 16 and spectrograph attaced. This is a challenging load as the spectrograph is quite long and assembled from several components. The mount does not have encodes on the axis but you can still use a pointing/tracking model. I don't bother guiding as I take short exposures (10 -25 s) .

For interest I measured the drift over 4 hrs 13 min of exposures last night. It drifted 1 arc sec in RA and 85 in Dec so about 0.33 arc sec per min.

I suspect the Dec drift is due to the spectrograph and a stiffer imaging rig would be better modeled. 

Anyway just for interest, it show you can use modeling without encoders.

Here is the spectrograph. 

Regards Andrew 

Edited May 1, 2020 by andrew s

[vlaiv]

12 hours ago, RayD said:

Agreed.  But I do 20 minute subs so how does that help me?

I was just pointing out that most people who don't guide suffer from periodic error and if they want to continue imaging without guiding - they are better of having mount with encoder/encoders.

It is a trade-off, you don't spend money on laptop, guide camera, guide scope/oag and all those bits and you spend your money on encoder. You then don't worry about parameters for guiding and just image.

This approach has its limitations - like you say, you can't do 20 minute subs in high resolution or whatever - but for some people - it is the way they like doing things.

Otherwise - just guide. I'm fan of guiding and I would not image unguided.

I'm still not sure what about my recommendation was misplaced. I simply recommended EC version based on whether one expect to guide or not.

Maybe this is interesting point:

11 hours ago, Jkulin said:

The EC encoders on the RA help guiding immensely, but they were never designed to replace the need for guiding.

Could you be more specific about how encoders help guiding immensely?

For example, would 120 mount be guided 0.7" RMS without encoders and 0.3" RMS with encoders or something like that?

From specs (which might be wrong, but let's not complicate discussion with that as well) - PE is less or equal to +/-3.5". That is 7" P2P and 240s worm period. Let's assume that all of 7" was traveled in only 1/3 of worm period, then RA drift rate is 7/80 = 0.0875.

Let's assume that you guide with 4s cycle, that is 0.35 error. It follows that you can't really have more than 0.35" RMS in RA. How much can encoders improve on that?

[RayD]

45 minutes ago, vlaiv said:

I'm still not sure what about my recommendation was misplaced. I simply recommended EC version based on whether one expect to guide or not.

I never said it was misplaced. I think it was, and is, perfectly valid.  However, I'm not trying to prove you wrong, I simply offered my view on your question of why one would spend extra money for encoders when guiding.

Edited May 1, 2020 by RayD

[RayD]

1 hour ago, andrew s said:

I have a Paramount ME II with a OO ODK 16 and spectrograph attaced. This is a challenging load as the spectrograph is quite long and assembled from several components. The mount does not have encodes on the axis but you can still use a pointing/tracking model. I don't bother guiding as I take short exposures (10 -25 s) .

For interest I measured the drift over 4 hrs 13 min of exposures last night. It drifted 1 arc sec in RA and 85 in Dec so about 0.33 arc sec per min.

I suspect the Dec drift is due to the spectrograph and a stiffer imaging rig would be better modeled. 

Anyway just for interest, it show you can use modeling without encoders.

Here is the spectrograph. 

That's great.  I would much prefer to have a mount that uses modelling, such as the 10Micron etc than guiding.  Unfortunately I can't afford one 🙁