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I am going to upgrade to the skywatcher 250/1200 pds telescope and i can't decide which mount i should get.

The main (only) purpose is astrophtography and i am considering either the eq6-r- pro or the cem60

The cem60 can carry more weight but is also more expensive, my inner debate now is about if it is worth it

What's you take on it?

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Here is my opinion on the matter. Considering mid range budget AP mounts (stretching to top tier), here is a sort of progressive list with regards to expense and performance:

1. EQ6 / HEQ5

2. CEM60EC

3. MESU 200

I consider these three mounts (well first one is two mounts, but different by weight carry capacity - otherwise on par by performance) to be appropriately spaced in terms of performance/price ratio.

CEM60EC is about x2-3 more expensive than HEQ5/EQ6/R family - but it provides x2-3 the performance. Here I think of tracking / guiding / smoothness performance.

First ones are in 0.5-0.7" RMS class guided mounts, second one is 0.3" RMS class mount, and last one is 0.1" class mount. And according to this - you get what you pay for - no question about that.

I don't consider other parameters in this, like durability, serviceability, QC, ease of use / transport, etc - these are things that you also need to consider, but for me primary AP performance parameter is tracking accuracy and precision of guiding.

So is the CEM60EC worth price premium over EQ6? For AP it certainly is, if you have the funds and if you go by same parameters as I do.

Couple of notes in the end:

- I'm not quite sure how performance of CEM60 fares in comparison to that of CEM60EC, so that can be potential best by if they are similar in performance with non encoder CEM60 being significantly cheaper then the version with encoders.

- HEQ5/EQ6/R mounts don't give above performance out of the box - there is quite a bit of tuning and modding involved, and that drives their real price a bit up

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24 minutes ago, vlaiv said:

CEM60EC is about x2-3 more expensive than HEQ5/EQ6/R family - but it provides x2-3 the performance. Here I think of tracking / guiding / smoothness performance.

First ones are in 0.5-0.7" RMS class guided mounts, second one is 0.3" RMS class mount, and last one is 0.1" class mount. And according to this - you get what you pay for - no question about that.

I own an EQ6-R and out of the box it guides 0.5"-0.8" usually, depending on the declination. Sometimes it's even better/worse (0.4" or 0.9"), depending on seeing too.

I've a few astro friends who own CEM60s. Some with encoders, some not. They report the guiding in between 0.4"-0.7" usually. I wouldn't really say the CEM60 provides x2-3 the performance. But without encoders, the price is less than 50% higher for the CEM60 compared to the EQ6-R.

In any case, some other pros for the CEM60:
- much lighter compared to the EQ6-R. ~12kg vs ~17kg
- has a native ASCOM driver, whilst with the SkyWatchers you need to use EQASCOM. Some people really like EQASCOM, but I found polar alignment without seeing Polaris cumbersome compared to the handset routine.
- USB hub build into the mount (2.0 only though and not powered)
- cables ran through the mount's head
- slightly higher payload

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I would look at it a bit differently....

EQ6-R payload Max 20kg

250PDS =20kg....

in my opinion, - PDS is too heavy for EQ6-R....

Just keep in mind, - You will add Coma Corrector, guiding scope, guiding cam, cables, USB hub...  Plus Main camera, if you will go mono, - filter wheel...

If you will go for Mods, - Primary mirror cooler (you will need large one) and etc and etc.

You will be over the optimum payload and sooner or later you will start looking at your Mount list again 

Edited by RolandKol
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3 minutes ago, RolandKol said:

I would look at it a bit differently....

EQ6-R payload Max 20kg

250PDS =20kg....

in my opinion, - PDS is too heavy for EQ6-R....

Just keep in mind, - You will add Coma Corrector, guiding scope, guiding cam, cables, USB hub...  Plus Main camera, if you will go mono, - filter wheel...

I you will go for Mods, - Primary mirror cooler (you will need large one) and etc and etc.

You will be over the optimum payload and sooner or later you will start looking at your Mount list again 

SkyWatcher say that the 250 DS is 14.38kg. https://www.skywatcher.com/product/bkp-250-ds/

Indeed, you'll need to add to that.

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2 minutes ago, alexbb said:

SkyWatcher say that the 250 DS is 14.38kg. https://www.skywatcher.com/product/bkp-250-ds/

Indeed, you'll need to add to that.

yep... I checked on other web and probably it has no Shipping before Weight...

My bad... anyway. 15kg plus all the toys on top and he will be at the edge of the optimal limits.

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3 minutes ago, chris_33 said:

thank you all very much, i am going for the cem60 :)

I don't think it's a bad idea :)

Please let us know how it performs.

Clear skies!

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49 minutes ago, alexbb said:

I own an EQ6-R and out of the box it guides 0.5"-0.8" usually, depending on the declination. Sometimes it's even better/worse (0.4" or 0.9"), depending on seeing too.

I've a few astro friends who own CEM60s. Some with encoders, some not. They report the guiding in between 0.4"-0.7" usually. I wouldn't really say the CEM60 provides x2-3 the performance. But without encoders, the price is less than 50% higher for the CEM60 compared to the EQ6-R.

In any case, some other pros for the CEM60:
- much lighter compared to the EQ6-R. ~12kg vs ~17kg
- has a native ASCOM driver, whilst with the SkyWatchers you need to use EQASCOM. Some people really like EQASCOM, but I found polar alignment without seeing Polaris cumbersome compared to the handset routine.
- USB hub build into the mount (2.0 only though and not powered)
- cables ran through the mount's head
- slightly higher payload

From what I've seen reported on internet, previous iteration of CEM60EC had factory specs of less than 0.6" RMS "on shaft" - via external encoder.

This is now changed to 0.3" RMS with GEN2 model. Here are official specs:

https://www.ioptron.com/product-p/7201.htm

And to quote spec from the page:

PE     < 0.5 arcsec rms for 5 min (< 0.3 arcsec for 2nd GEN)

I'm aware that some of these specs should be taken with grain of salt, but I'm also aware that reported guiding performance depends on various factors - like used guide scope resolution/precision, PHD2 settings, guide exposure duration and such.

Therefore I think that one can get 0.3" RMS out of CEM60-EC (not sure about CEM60 without encoders) - with attention to detail (like balance, guide settings and such, after all, I need to do it with my HEQ5 to get to 0.5" RMS, so I'm expecting that no mount can compensate for sub optimal usage).

   

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I kinda think even CEM60 will not be enough for 250PDS... 

It is my guess... Blind guess, -  as I have never had CEM60, I do have an old NEQ6 and I am sure I would never put 250PDS on it as even my 130PDS sometimes is guided above 1RMS.

250PDS is large... I mean.. Very Large.... I had 250 DOB. 

I simply afraid to think how it will look like on the Entry level mounts..... Any slight bit of the wind... And your PHD graph will go insane...
Not sure about your location, 

but if you are UK based, - we have so little clear nights to waste them...

 

Edited by RolandKol

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P.S.  a guick google search "best mount for 250PDS" and results, - in controversy to my opinion, - majority went for NEQ6.

I found it a bit strange... 

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11 minutes ago, RolandKol said:

I kinda think even CEM60 will not be enough for 250PDS... 

It is my guess... Blind guess, -  as I have never had CEM60, I do have an old NEQ6 and I am sure I would never put 250PDS on it as even my 130PDS sometimes is guided above 1RMS.

250PDS is large... I mean.. Very Large.... I had 250 DOB. 

I simply afraid to think how it will look like on the Entry level mounts..... Any slight bit of the wind... And your PHD graph will go insane...
Not sure about your location, 

but if you are UK based, - we have so little clear nights to waste them...

One of the reasons why your RMS goes wild with wind (apart from scope size) is backlash.

Worm gear motion transfer is pretty much - one way. So you can't move mount motor with your hands by moving scope. Due to this, wind acts in two ways - first is flexing OTA and moving complete scope/mount/tripod assembly. Stiff OTA and connection to mount and very stable tripod will lessen this impact. And there is issue of worm / worm gear backlash. If these are with minimal backlash and no slack between them and casing (properly tuned) - you get much better "wind" performance.

This is where CEM60 has significant + over (H)EQ class - it has magnetic coupling between worm / worm gear. It is not fixed - it can "breathe", but magnetic coupling prevents backlash as it always applies enough pressure to keep them coupled.

Edited by vlaiv
typo
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1 minute ago, RolandKol said:

I kinda think even CEM60 will not be enough for 250PDS... 

It is my guess... Blind guess, -  as I have never had CEM60, I do have and old NEQ6 and I am sure I would never put 250PDS on it as even my 130PDS sometimes is guided above 1RMS.

250PDS is large... I mean.. Very Large.... I had 250 DOB. 

I simply afraid to think how it will look like on Entry level mounts..... Any slight bit of the wind... And your PHD graph will go insane...
Not sure about your location, 

but if you are UK based, - we have so little clear nights to waste them...

As Vlaiv said above, you might need to pay more attention to balancing and guide settings. Or consider servicing your mount. OTOH, SkyWatcher mounts performance is know to vary form one to another very much. Whilst Vlaiv's HEQ5 guides at 0.5" with fine tuning, my AZ-EQ5 was "tuned" by DarkFrame and I got back a mount with ~70" periodic error. I can barely get to 1.2" RMS on short periods. Last night it was guiding 1.8"-2.0" RMS.

Personally, my greatest fear about a 10" newton is the wind. But then, most probably, the seeing would be bad as well.

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55 minutes ago, RolandKol said:

P.S.  a guick google search "best mount for 250PDS" and results, - in controversy to my opinion, - majority went for NEQ6.

I found it a bit strange... 

when you search for the telescope on astrobin you also find a lot of pictures with an eq6: https://www.astrobin.com/search/?q=skywatcher+254%2F1200&amp;d=i&amp;t=all

 

56 minutes ago, alexbb said:

Personally, my greatest fear about a 10" newton is the wind. But then, most probably, the seeing would be bad as well.

yeah, wind is also something i have in mind, but as far as i remember luckily we don't have much on clear nights

with the 1200mm and my dslr i am at 0.823"/pixel, seeing in winter is around 0.9" to 1", in summer it's better, so i figured that 10" is the biggest that still makes sense (also with 12" you would need a bigger mount that would exceed my budget quite a bit)

 

 

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Hi,

One important point worth mentioning is how is the RA and DEC head fixed to the part which goes to be it a tripod  or a pier. A tripod from nature is always less stable then a pier.

A tripod, and those who make terrestrial photography know it, has always the tendency to move in rotational direction.  This depends always from the type of the construction of how the legs are fixed to the tripods head. This is one thing.

One important point between a stable and a less stabe mount is what I mentioned before.

I have had experience with Losmandy G11 mounts and have had my hands on a iOptron CEM 60 mount and so I could experience the difference. It is always better to have a broad base instead as a fork and an insert holding the RA / DEC head.

Look at the 2 images comparing the attachment to the mounts base.

BTW, the Losmandy G11 tripod is the best what I have ever had in tripods for mounts. No rotational movement at all and even used it for the big big CEM 120EC2.

Rainer

 

CEM60_base.JPG

G11-base_attachment.jpg

IMG_3609_C1 (2).jpg

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No one outside China appears to have received one yet.

But since they are at the New York trade show soon, and are known to sell their display models instead of shipping them back, i expect some first hand account in a few weeks.

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Just to emphasize the points made about the size of the  PDS.  Not only is it heavy but it is big and fat, high windage and long levers with quite a long focal length.  I imagine both the EQ6-R and the CEM will be fine when there is little wind around but as the breeze picks up you are going to run into trouble unless you are nicely sheltered e.g. in a dome.  Backlash is just one factor, there will be significant flexing forces on your mount, and your dovetail/tube rings.  Your productivity is very likely to be reduced going for a 10" rather than an 8" reflector if you are out in the open.

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