Eq8 or CEM120

[Nigella Bryant]

3 hours ago, Rainer said:

OH I see quite long telescopes and ehre the weight is not relevant but the moment arm and how much it acts as a sail ...

Maybe a Truss Newtonian and not a tube Newtonian ?

Surely it wouldn't act much of a sail considering it's housed in an observatory dome. The only huge momentum would be while slewing to an object, perhaps two or three at most during a nights imaging?

[Rainer]

29 minutes ago, Nigella Bryant said:

The only huge momentum would be while slewing to an object,

For me that is not a problem.

But are you sure a Dome inhibits Air Currents ? I have never had a dome but the wind gets in everywhere ¿ or ?

Rainer

[Nigella Bryant]

10 minutes ago, Rainer said:

For me that is not a problem.

But are you sure a Dome inhibits Air Currents ? I have never had a dome but the wind gets in everywhere ¿ or ?

Rainer

Hiya, never had any problems with wind, except for too many beritos, lol. As I'd said b4, my current set up of an 12inch f4 1200mm 4ft scope on an neq6 performs well but I kmow it's well over load and with an option to upgrade to a 16inch a new mount is overdue. 

[MakeItSo]

Hi Nigella, 

Which mount did you end up going for? I have more or less the same decision to make, pending getting the all clear on building my ROR. 

Best,

Simon

[ollypenrice]

What do you expect to gain from the 16 inch for deep sky imaging? The 12 inch has a FL of  1.2 metres. The 16 has a FL of 1.6 metres. A FL of 1.2 metres with modern cameras will easily take you to an image scale of below, or even well below, an arcsecond per pixel. What resolution will your sky support?  If it will support scales below an arcsecond, at least on any kind of regular basis, I'd be amazed and would be similarly amazed if the theoretical gain in optical resolution would translate into new details resolved on the image. We are seeing-limited.  I'm struggling to find much improvement in resolution when comparing data from a 5.5 inch refractor at 0.9"PP with data from a 14 inch reflector working at 0.6"PP. (Different cameras.)

I ask this because the big scope is part of your mount game plan. Personally I'd go for the bigger aperture for visual but not for imaging. I can't see the point. I think you'll end up with the same final resolution and a smaller FOV.

In any event, even the 12 inch can take you into imaging territory where you'll want a guide RMS of 0.4" and that's a high level of precision. For me the EQ8 is a big hefty mount more than it is a high precision one and for that reason I'd go for the iOptron. (That is if I couldn't find a second hand Mesu. Both mine cost less than the new price of the iOptron.)

Olly

Edited June 17, 2019 by ollypenrice

[cotak]

Used mesu is a mythical creature over here in Canada. So few owners likely wouldn't be much cheaper. Thanks to our crazy shipping costs. 

Edited June 17, 2019 by cotak

[vlaiv]

17 minutes ago, ollypenrice said:

What do you expect to gain from the 16 inch for deep sky imaging? The 12 inch has a FL of  1.2 metres. The 16 has a FL of 1.6 metres. A FL of 1.2 metres with modern cameras will easily take you to an image scale of below, or even well below, an arcsecond per pixel. What resolution will your sky support?  If it will support scales below an arcsecond, at least on any kind of regular basis, I'd be amazed and would be similarly amazed if the theoretical gain in optical resolution would translate into new details resolved on the image. We are seeing-limited.  I'm struggling to find much improvement in resolution when comparing data from a 5.5 inch refractor at 0.9"PP with data from a 14 inch reflector working at 0.6"PP. (Different cameras.)

I ask this because the big scope is part of your mount game plan. Personally I'd go for the bigger aperture for visual but not for imaging. I can't see the point. I think you'll end up with the same final resolution and a smaller FOV.

In any event, even the 12 inch can take you into imaging territory where you'll want a guide RMS of 0.4" and that's a high level of precision. For me the EQ8 is a big hefty mount more than it is a high precision one and for that reason I'd go for the iOptron. (That is if I couldn't find a second hand Mesu. Both mine cost less than the new price of the iOptron.)

Olly

There is a lot to be gained by using 16" F/4 scope (I'm guessing it is F/4 scope because you mentioned 1600mm FL).

Take for example difference to my 8" RC. I use it with ASI1600 - it's oversampling at 0.5"/px, but binning sorts that out, and I usually consider my images to be between 1.5"/px and 1.0"/px (x3 or x2 bin).

16" F/4 scope will work with the same sampling rate as my 8" RC, but will have x4 light gathering capacity. I would not mind having a scope that will gather x4 more light and keep similar "properties" as my current imaging scope.

[ollypenrice]

Just now, vlaiv said:

There is a lot to be gained by using 16" F/4 scope (I'm guessing it is F/4 scope because you mentioned 1600mm FL).

Take for example difference to my 8" RC. I use it with ASI1600 - it's oversampling at 0.5"/px, but binning sorts that out, and I usually consider my images to be between 1.5"/px and 1.0"/px (x3 or x2 bin).

16" F/4 scope will work with the same sampling rate as my 8" RC, but will have x4 light gathering capacity. I would not mind having a scope that will gather x4 more light and keep similar "properties" as my current imaging scope.

That's not what I'm saying. Note that I'm comparing a 12 inch F4 with a 16 inch F4, not a 16 inch with the same FL as the 12 inch. The question is not whether a small scope and a large of the same focal length will be equivalent. They won't, as you say. The question is, what will the OP gain by moving from a 12 inch F4 to a 16 inch F4 bearing in mind the FL will increase? In my opinion both will be seeing-limited and risk resolving detail at the same level but with a loss of FOV in the large one. 

Olly

[vlaiv]

1 minute ago, ollypenrice said:

That's not what I'm saying. Note that I'm comparing a 12 inch F4 with a 16 inch F4, not a 16 inch with the same FL as the 12 inch. The question is not whether a small scope and a large of the same focal length will be equivalent. They won't, as you say. The question is, what will the OP gain by moving from a 12 inch F4 to a 16 inch F4 bearing in mind the FL will increase? In my opinion both will be seeing-limited and risk resolving detail at the same level but with a loss of FOV in the large one. 

Olly

Same difference Although "speed" of the scope stays the same, "speed" is not really the speed of gathering photons. Best to think of it as "aperture" at certain pixel scale. As you pointed out, both scopes will over sample on most cameras (pixel sizes) and there will definitively be some binning involved to get to proper scale. If we consider that, then both scopes can be matched with a camera and bin factor to produce same target sampling rate.

16" vs 12" at same target sampling rate - more photons in first case.

Another important fact to consider with this type of reasoning is available FOV - longer FL will reduce FOV, so that should be taken into account when considering scope.

[ollypenrice]

1 hour ago, vlaiv said:

Same difference Although "speed" of the scope stays the same, "speed" is not really the speed of gathering photons. Best to think of it as "aperture" at certain pixel scale. As you pointed out, both scopes will over sample on most cameras (pixel sizes) and there will definitively be some binning involved to get to proper scale. If we consider that, then both scopes can be matched with a camera and bin factor to produce same target sampling rate.

16" vs 12" at same target sampling rate - more photons in first case.

Another important fact to consider with this type of reasoning is available FOV - longer FL will reduce FOV, so that should be taken into account when considering scope.

Isn't that exactly what I said???

lly

 

[vlaiv]

21 minutes ago, ollypenrice said:

Isn't that exactly what I said???

lly

 

I was just pointing out that larger scope means more aperture, and as such has benefits for target resolution - it will collect more photons and will be faster.

[ollypenrice]

2 minutes ago, vlaiv said:

I was just pointing out that larger scope means more aperture, and as such has benefits for target resolution - it will collect more photons and will be faster.

 Larger scope means more aperture? Damn, I hadn't thought of that!!! 

Seriously, I think everything I have to say is included in my first post which is strictly devoted to comparing 12 inch F4 and 16 inch F4. Where, in your view, does the 16 inch win in seeing which is limited to, say, an arcsec per pixel?

(I always enjoy our disagreements!)

Olly

[vlaiv]

1 hour ago, ollypenrice said:

 Larger scope means more aperture? Damn, I hadn't thought of that!!! 

Seriously, I think everything I have to say is included in my first post which is strictly devoted to comparing 12 inch F4 and 16 inch F4. Where, in your view, does the 16 inch win in seeing which is limited to, say, an arcsec per pixel?

(I always enjoy our disagreements!)

Olly

No, it's not about resolution / resolving power (yes, 16 inch will have small theoretical advantage even in poor seeing, but that is besides the point).

Your post that I first answered to, stated that you can't see any advantage in going with larger scope. I offered distinct advantage of larger scope - it will be faster for given target sampling rate. If one is willing to sacrifice FOV (has reasonably large sensor for intended targets), will bin data anyway, then why not go for biggest aperture one can handle?

[ollypenrice]

18 minutes ago, vlaiv said:

No, it's not about resolution / resolving power (yes, 16 inch will have small theoretical advantage even in poor seeing, but that is besides the point).

Your post that I first answered to, stated that you can't see any advantage in going with larger scope. I offered distinct advantage of larger scope - it will be faster for given target sampling rate. If one is willing to sacrifice FOV (has reasonably large sensor for intended targets), will bin data anyway, then why not go for biggest aperture one can handle?

It won't be faster if the imager has to do a mosaic to replace the reduced FOV.

If we allow ourselves complete freedom to invent any camera we like then the 16 inch will beat the 12 inch because we can invent a camera with a larger chip to replace the lost FOV of the 16 inch (though we might need to invent a new coma corrector as well). We can also invent a camera for the 16 inch which has not only a larger chip to restore the FOV of the 12 inch but also has larger pixels to hit the sweet spot of 0.9"PP (or whatever). The problem is, once we have invented these cameras do we know anyone twitching with enthusiasm to make them for us? And since the future seems to be moving away from CCD and towards CMOS the simple binning solution (which I have never believed was that simple anyway since not all cameras bin well) becomes not so simple.

Olly

[Datalord]

Olly, I actually understand your argument and I can see why it is true in one way. But I also disagree in that comparing scopes based on FOV is artificial. 

I went from a 11" f2.2 to a 12" f8. Biggest difference you can imagine. And I would not shoot the same targets, that would be nonsense. But the rc gives me access to more objects, which space is gloriously full of. If I could have Hubble's 54.000mm FL I would use that for fun new targets. I would not go for Orion with it. 

I propose these recurring discussions take their beginning with: "what targets do you prefer?". Then comes finding the scope/camera combination that suits this best.

If I were looking at 12" f4 vs 16" f4, they are in my world virtually the same. The targets you can acquire are virtually the same. What you do get is simply more photons hitting the camera, which does translate to improvement in signal to noise, for the given camera surface. Faster and better pictures. 

I would not bother. A 16" RC on the other hand would be a completely new world of wonder opening up, alas also incredible pain. 

[pete_l]

8 hours ago, Datalord said:

I went from a 11" f2.2 to a 12" f8. Biggest difference you can imagine. And I would not shoot the same targets, that would be nonsense. But the rc gives me access to more objects, which space is gloriously full of.

I agree. There are far more small and interesting targets than large and interesting ones.

We tend to pay a lot of attention to the "crowd pleasers" M42, Andromeda, N. America neb etc. I can understand why: they are quick to image and produce nice, bright, colourful results. But imaging small stuff takes time. It also takes money as the kit needed is larger, higher quality and more complex. There is obviously room for all-comer in the hobby.

But ultimately it IS a hobby, not a competition. Once it stops pleasing people, that's the time to stop.

[ollypenrice]

8 hours ago, Datalord said:

Olly, I actually understand your argument and I can see why it is true in one way. But I also disagree in that comparing scopes based on FOV is artificial. 

I went from a 11" f2.2 to a 12" f8. Biggest difference you can imagine. And I would not shoot the same targets, that would be nonsense. But the rc gives me access to more objects, which space is gloriously full of. If I could have Hubble's 54.000mm FL I would use that for fun new targets. I would not go for Orion with it. 

I propose these recurring discussions take their beginning with: "what targets do you prefer?". Then comes finding the scope/camera combination that suits this best.

If I were looking at 12" f4 vs 16" f4, they are in my world virtually the same. The targets you can acquire are virtually the same. What you do get is simply more photons hitting the camera, which does translate to improvement in signal to noise, for the given camera surface. Faster and better pictures. 

I would not bother. A 16" RC on the other hand would be a completely new world of wonder opening up, alas also incredible pain. 

We seem to come to the same conclusion here. I very much doubt that real results would change by much.

If you have a site with exceptionally stable seeing the 16 inch RC would indeed deliver a new world of wonders. In most parts of the world, however, it would deliver a shedload of 'empty resolution' onto a minute FOV!

I didn't want to sidetrack the mount thread but merely raise the issue of the value of this increased payload because that might impact on mount choice.

Olly

 

 

[Nigella Bryant]

Thanks everyone, goodness a very good discussion. I've obviously not thought thing's through enough. After all I'd be talking a good part of £6,000 for changing my mount and scope. The mount I've still yet to decide upon, but that's the priority as my neq6 is at top load capacity of 20kg. I'll be keeping my 12inch f4 Newtonian for some time yet, so the mount is priority this year. I'm not in a rush and obviously don't want to make the wrong decision. I understand skywatcher is bringing out a new mount next year with more payload than a cem60 but similar design. Probably somewhere between a CEM60 and a CEM120. Seen some illustrations of the mount. I may hold off until then and see. I'm not deffinet on upgrading to a 16inch f4 Newtonian anytime soon. Thanks all, alway's a great debate with much that washes over my head I'm afraid. 

[tonyowens_uk]

I'm late coming to this discussion - apologies. One potentially interesting avenue to consider, against the CEM120 and upcoming centre-mount competitor model from Skywatcher, is an upgraded EQ8. I need to disclose that I make these so have a vested interest. But ignoring that for a minute. Some of my spare time over the last few years has gone into sorting out the limitations of this mount and this has been quite successful. Imaging load capacity, and guiding responsiveness and accuracy are significantly improved due to use of stiffer ground steel shafts in place of the aluminium originals combined with different worm bearings, damped, diamond-lapped antibacklash gears and now a new ASCOM server named Green Swamp, specifically designed for this mount. Through-the mount cabling is relatively trivial to implement if needed as the axes are hollow. Custom saddle plates for larger instruments and cranked piers for eliminating meridian flips are straightforward too.

This route makes sense for those more interested in functionality than 'bling'. Specifically, for people who:

1. already own early EQ8's with large Dec backlash issues which make good imaging difficult

2. need a reliable, economical, heavy imaging mount/s for remote use, and are unconvinced of the superiority or practicality of unguided encoder mounts

3. are willing to consider buying a cheap used EQ8 as a basis for upgrade

The cost of our modernisation runs 1200-2000 euros plus VAT where applicable, depending on spec. 

[StarDodger]

3 hours ago, tonyowens_uk said:

I'm late coming to this discussion - apologies. One potentially interesting avenue to consider, against the CEM120 and upcoming centre-mount competitor model from Skywatcher, is an upgraded EQ8. I need to disclose that I make these so have a vested interest. But ignoring that for a minute. Some of my spare time over the last few years has gone into sorting out the limitations of this mount and this has been quite successful. Imaging load capacity, and guiding responsiveness and accuracy are significantly improved due to use of stiffer ground steel shafts in place of the aluminium originals combined with different worm bearings, damped, diamond-lapped antibacklash gears and now a new ASCOM server named Green Swamp, specifically designed for this mount. Through-the mount cabling is relatively trivial to implement if needed as the axes are hollow. Custom saddle plates for larger instruments and cranked piers for eliminating meridian flips are straightforward too.

This route makes sense for those more interested in functionality than 'bling'. Specifically, for people who:

1. already own early EQ8's with large Dec backlash issues which make good imaging difficult

2. need a reliable, economical, heavy imaging mount/s for remote use, and are unconvinced of the superiority or practicality of unguided encoder mounts

3. are willing to consider buying a cheap used EQ8 as a basis for upgrade

The cost of our modernisation runs 1200-2000 euros plus VAT where applicable, depending on spec. 

Have you got any pictures of the mounts after the mod.. ? I would like to see how it looks..

and what exactly does the mod involve.. to eliminate the issues that comes with these mounts...

i Just got hold of a secondhand d EQ8 for a very very good price, under £1200 and it’s mint (well after swapping all the bolts for stainless steel ones anyway) and one of the later ones it’s 3 years old..

Edited July 3, 2019 by StarDodger

[tonyowens_uk]

3 minutes ago, StarDodger said:

Have you got any pictures of the mounts after the mod.. ? I would like to see how it looks..

and what exactly does the mod involve.. to eliminate the issues that comes with these mounts...

i Just got hold of a secondhand d EQ8 for a very very good price, under £1200 and it’s mint (well after swapping all the bolts for stainless steel ones anyway) and one of the later ones it’s 3 years old..

There will be a website at some point but finding time is an issue for me.

There is a special interest Yahoo Group about EQ8's here that includes various contributions from me about the project here: https://groups.yahoo.com/neo/groups/SkywatcherEQ8/info

 

Pictures of the mount and our shipping crate for couriered collection and return:

 

Picture of before and after polar plots (5 test points, equally-spaced around each axis) showing the effect of the new gearing on backlash as benchtested:

 

Dec Backlash as tested on the sky with PHD2 and a 1180mm EFL 20 Kg autoguiding payload:

 

The autoguiding performance has been tested and shows around 4" pk-pk periodic error for the new RA gearing, which corrects down to 0.40" RMS on RA and 0.35" RMS on Dec with careful tuning of settings on PHD2. There is some work still ongoing on improved autoguiding involving different motor firmware and a new ASCOM server which offers certain advantages over EQMOD in principle, and perhaps also in practice. We shall have to see!

Tony Owens

[StarDodger]

8 minutes ago, tonyowens_uk said:

There will be a website at some point but finding time is an issue for me.

There is a special interest Yahoo Group about EQ8's here that includes various contributions from me about the project here: https://groups.yahoo.com/neo/groups/SkywatcherEQ8/info

 

Pictures of the mount and our shipping crate for couriered collection and return:

 

Picture of before and after polar plots (5 test points, equally-spaced around each axis) showing the effect of the new gearing on backlash as benchtested:

 

Dec Backlash as tested on the sky with PHD2 and a 1180mm EFL 20 Kg autoguiding payload:

 

The autoguiding performance has been tested and shows around 4" pk-pk periodic error for the new RA gearing, which corrects down to 0.40" RMS on RA and 0.35" RMS on Dec with careful tuning of settings on PHD2. There is some work still ongoing on improved autoguiding involving different motor firmware and a new ASCOM server which offers certain advantages over EQMOD in principle, and perhaps also in practice. We shall have to see!

Tony Owens

Thanks for that...

so not a spring loaded worm then..? Just new bearings and well tuned..and maybe new worm..?

 

[pete_l]

Very interesting Tony. At first glance the charts showing the improvement in RA and Dec backlash don't look that impressive. Then I saw the difference in scale! 5000 vs 1000. 🤯

I also found your web page of the Synta EQ8 Re-imagined. I will follow the project with interest.

[tonyowens_uk]

This is a different animal than a 'hypertune' or even an aftermarket worm. There are fundamental problems with the design of clutches and choice of worm and shaft bearings in the EQ8 which were addressed to some extent by the manufacturer after a mixed reception to the original product. I was one of the victims in fact...

The eventual result of my efforts was a new form of antibacklash worm gearing that also includes constrained layer damping to lower the meshing noise 'floor'. Also a redesigned clutch that can be tightened without imposing radial load on the shaft and inducing backlash and an image shift. Improved environmental sealing and a precision transfer timing belt drive to RA and many other improvements are there too. In combination with some other changes it amounts to a modernisation not an overhaul. A UK patent application on the gearing was filed at the end of 2018.

The effect is that there is no significant backlash on either axis, regardless of axis position, ambient temperature or wear. Nothing to fiddle with - the mount 'just works', as it should have done back in 2014 when I bought mine!

 

Tony

[Nigella Bryant]

Update, I ended up with the Eq8 r pro mount. Only recently though. Covid hit and I couldn't get my hands on a mount until recently. Not really used in anger yet as I've had awful weather. Just installed in the dome and did a home sync and connected everything up. Usb3 hub works with my zwo camera's too. 

Edited November 23, 2021 by Nigella Bryant
Pic added