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Skywatcher 16" (400P) on a EQ6 PRO Mount

MichaelBruno

By MichaelBruno
in Discussions - Mounts

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MichaelBruno

MichaelBruno

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I recently purchased an Skywatcher EQ6 PRO Equatorial Mount.

At the moment I have an 8" Orion on the mount.

I was waiting patiently for the Skywatcher 14" 350P tube to come to South Africa, but upon querying the local supplier I found out that Skywatcher have now also launched a 16" 400P tube!

My interest in long exposure astrophotography, so the equatorial mount (as opposed to ALT-AZI) is a must.

I am very curious as to whether anyone has considered, or better yet, tried mounting a Skywatcher 16" 400P on an EQ6 PRO mount.

I would think that to be a dream amateur astrophotographers setup?

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johninderby

johninderby

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I believe that SkyWatcher has delayed the release of the 16" for a few more months so I don't think anyone has actually seen one yet.

Unfortunately you'll need something heavier duty than the EQ6 for the 14" even just for visual, and I'd hate think how shaky it would be with the 16".

John

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MichaelBruno

MichaelBruno

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Thanks John, Ben and John for the prompt feedback.

Not the verdict I was hoping to hear!

Not completely discouraged (yet) I have a few specific questions:

a. Would the 16" actually physically fit and allow full telescope swing to the zenith?

b. If it does actually fit, then is the concern mostly wind shudder / stability?

c. If wind shudder / stability is the problem, then will a pedestal mount to concrete base not fix that problem?

d. Or is the problem the weight of the tube on the gears of the EQ6 Pro?

e. If the problem is weight, then will the addition of extra counterweights not help with that?

Sorry for the detailed questions, and thanks for any further thoughts.

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MichaelBruno

MichaelBruno

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Yip, I heard about the EQ7 today as well.

Wish I'd known about that 3 months ago!

I was told it would be available in South Africa at approx US$7700 in January 2011. I paid US$4300 for my EQ6 Pro 3 months ago, and thought that was going to do me proud to the end of days.

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Ben Ritchie

Ben Ritchie

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Sorry for the detailed questions, and thanks for any further thoughts.

There are limits to the counterweights you can have on an EQ6, the counterweight bar is not that strong - I have three counterweights on mine for a 5" refractor + 3" piggyback, and wouldn't want to put many more on. The 350p OTA is far, far heavier than that, with weight further out from the mount (due to its increased size). I don't believe that there would be any way to make it balance without major modifications to the counterweight bar. And then i'd have concerns about the ability of the mount head and gearing to cope, plus you have zero margin for error in the balancing.

A secondary concern isn't just weight, it's the ability of the 350p/400p structure to be mounted on an EQ via just a dovetail. I don't think it's rigid enough. Again, it's hard to stress quite how big the 14" is - it's a whole different league than the 12"

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sixela

sixela

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There's also the question of "why".

Very few people will benefit from a focal ratio much faster than f/5 or so and a focal length beyond 1500mm (unless, of course, you're thinking about exotics like a 1m Schmidt camera with flattener), and DSO astrophotography is not a game where aperture trumps most other things, unlike visual observation.

And if you want a larger image scale, the mount's stability is the first thing that has to be absolutely perfect. You have an EQ6, and I have a hard time imagining that anything more than a 250mm Newt, or if you want more image scale a C11 with reducer or something like a simlarly sized Ritchey Chrétien, would make sense on it.

I don't have the definitive answer, but I suspect most astrophotographers would say the same. If they wanted more resolution to catch even the smallest of objects at the limits of seeing, I suspect most of them would be looking at sensors with smaller pixels first rather than an even larger Newt on top of the mount.

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johninderby

johninderby

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To help with the size comparison here's a photo of my 14" dob next to a 10" dob. 4" difference in aperture doesn't seem like that much of a difference until you put the two OTAs side by side :) and a 10" OTA is a lot bigger than an 8" OTA such as you're using now.

John

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MichaelBruno

MichaelBruno

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The reason "Why" :

My limited understanding tells me that a bigger aperture will capture more detail with shorter exposures.

This is especially important to me since my camera is a standard unmodified DSLR Canon 550D, and continuous long exposures (beyond 30 seconds) are not recommended due to internal heating.

And of course, not being a pro, I would like to have a setup that achieves best bang for buck for observational use as well as astro-photography.

It is perhaps worth factoring in that the Skywatcher 14" and 16" are retractable tube comparatively lightweight telescopes, as per the attached pic.

post-22269-133877504211_thumb.jpg

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johninderby

johninderby

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One thing to note is that a solid tube OTA will actually be lighter than the SkyWatcher truss tube. That truss tube mechanism will weigh more than the equivalent length of solid tube that it replaces.

I use a 14" Orion Optics UK dob and the tube is fairly lightweight as they use an aluminium tube. SkyWatcher uses steel tube.

John

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MichaelBruno

MichaelBruno

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The other reason why :

An EQ6 Pro mount cost me US$4300.

A Skywatcher 16" Tube will cost around US$2500.

At a total cost of US6800, that would be an awesome setup.

Not sure what an APO 250mm might cost, but I'm pretty sure it would be far more than the Skywatcher 16".

Also, in ignorance of refractors for astrophotography, 250mm doesn't sound all that much better than the 8" 200mm Orion I'm currently spending my nights in front of.

Thanks John Inderby for all the 14" size and weight insight... you've got me feeling dubious about my ambitions here :)

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GazOC

GazOC

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TBH Michael the cost is irrelevant, the setup just won't work, what you are suggesting isn't a borderline call or something that may work after a fashion if certain modifications are made to the mount. Its just a complete non-starter.

If you want to observe and image with the EQ6 you need to look at more realistic options like a 5" refractor, 8" Newt, 190mm Mak/Newt and just enjoy the 16" Skywatcher on the Dob mount.

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MichaelBruno

MichaelBruno

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Unfortunately that price is correct.

I have seen the U.S. and U.K. prices and cringe at how much we pay here. I even considered purchasing abroad and bringing it back in my suitcase at one stage!

That's what happens in a country without healthy competition between importers.

The price has since dropped to around US$4000, but only in response to a stronger South African Rand currency.

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MichaelBruno

MichaelBruno

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No John, I had not considered that...

I guess I assumed that the Synscan software in the dobsonian mount wouldn't know how to correct if the whole dob mount was pitched at 28 degrees.

Also not sure how I would achieve the South Celestial Pole alignment without a polar scope?

Without a convenient North celestial pole star down here in the south, it takes me hours to align the EQ mount as it is - even with a polar scope.

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MichaelBruno

MichaelBruno

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GazOC : Thanks for your practical recommendations & resolved opinion.

I'm keeping track of this thread in the hop that someone has actually tried at least a 14" Skywatcher on an EQ6 Pro.

If nobody has, then watch this space : I'll probably (and stupidly) be the first to try a 16" on one :)

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George

George

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I have the 250PX (10'') and a ED80 on my EQ6, that takes 4 counter weights to balance it (20kgs in total) I think Im not far off my mounts limit for imaging and never had any tracking/balance problems with my setup. There's 1 or 2 people on here with the 300PX (12'') on a EQ6 that they use for visual. A 350PX or 400PX IMHO would be beyond the mounts capabilities and no doubt you are entering AP1200 or the new EQ7 territory with your proposed setup.

I'd imagine the forces encountered stopping from a fast slew with a 14" or 16" OTA mounted would likely at the least strip the teeth from the crown wheel.

Forget about the EQ6 :)

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