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

[johninderby]

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.

You wouldn't use the synscan as the EQ table will do all the tracking. But however a Synscan dob would work really well with an EQ table as the OTA wouldn't shift while the EQ table was moving.

John

[DrNeb]

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

SWEET ZOMBIE JESUS!

that is huge!

[simon84]

I've not read through this thread totally but I bought the NEQ6/Explorer 300P combo when it was first available and it struggled with the scope and 4, yes 4, counterweights.

The counterweights had to put onto a 130mm long extension for the counterweight bar and that caused quite a bit of bending, it didnt like it at all.

The scope would shake for ages when trying to focus and imaging was an absolute no no unless it was lunar. The scope now has a moonlite focuser on it and for some bizarre reason I cannot balance the scope with the 4 counterweights on the extended bar......I'm now making a dob base for it.....

I've thought about popping the 300P on an EQ7 to image with but it really does depend on what the capacity of the EQ7 is going to be.

[Peter Drew]

Be carefull about EQ7's, Lidl are offering a 76mm Newt on an "EQ7" for Xmas priced at around £70. This "EQ7" looks about half the size of an EQ1 !. Back to the post, I think the best option would be an equatorial platform, these can be very accurate and weight is not an issue with a suitable one.

[ollypenrice]

The reason "Why" :

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

.

This is almost entirely wrong, which is good news because the setup you envisage would be an imager's nightmare and would never take a picture.

The exposure time depends only on f ratio. Yes, it does not sound remotely credible at first but so it is. A 60mm f4 Borg is fast, a 300mm f10 Celestron is slow, full stop. Aperture has no bearing on exposure time in itself.

Instead of thinking about aperture think about focal length and focal ratio. Fl will decide your image scale; will you have a narrow or a wide field. And f ratio will decide your exposure times. So what do you want to image? Small objects need a long Fl, large ones a short.

And I would say set f7.5 as an upper limit for f ratio.

Now think about tracking accuracy. An EQ6 has no hope whatever of humping a 16 inch Newt physically anyway, but that is only half the battle. The other half is tracking accuracy. I have two EQ sixes in commercial use and like them well enough. I feel they are reliable when asked to guide at a metre but beyond that they become increasingly marginal without a lot of input on the fine tuning side. They should not be asked to guide beyond two metres and I would set 1.5 as my own absolute limit. Overloaded they would be even less likely to cope.

Now take a metre Fl as a 'given'. Yes, you will in theory get more resolution and speed from a big corrected Newt than from a smaller alternative... but if the mount is trembling under the strain your small increase in resolution is gone. And would your seeing allow you to exploit it anyway?

You don't need a big scope to image. you need good optics on a mount that is well within its limits.

Olly

[darkly]

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

As above, I'm going to keep watching this thread, I'm watching this space Michael, on the edge of my seat - good luck

[noakesy]

i have 8in on heq5 what would be the biggest scope i could put on the as i was thinking of getting 10/12 in

[lukebl]

i have 8in on heq5 what would be the biggest scope i could put on the as i was thinking of getting 10/12 in

You're probably at the limit already.

[GazOC]

I've had a 10" f5 Newt on a HEQ5. It was OK for visual but right at the edge of what the mount can comfortably take IMHO.

[darkly]

i have 8in on heq5 what would be the biggest scope i could put on the as i was thinking of getting 10/12 in

Reading between the lines on this thread, I think 16" is about to 'become' possible

The 'skies the limit' (groan)

[John]

I popped into the Widescreen Centre in London last year. In their shop they have a 16" F/4 newtonian on an equatorial mount (not an EQ6 - this thing looked much beefier although the finish was not as glossy). The whole scope was immense and towered over everything else on the shop floor. Apparently it took 4 beefy chaps and a number of sets of short step ladders to get the OTA into the mount. The whole thing looked much, much larger and unwieldy than the 20" dobsonian I had a look through at the SGL star party this year.

[Whippy]

I popped into the Widescreen Centre in London last year. In their shop they have a 16" F/4 newtonian on an equatorial mount (not an EQ6 - this thing looked much beefier although the finish was not as glossy).

That mount was probably the Intes D6 mount John. It's a very beefy mount!

Tony..

[sixela]

The reason "Why" :

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

A bigger aperture with the same f/ratio will not capture with shorter exposures, but give you a larger image scale. But if the seeing blurs it anyway, there's no point. And in the case of your project, if the mount tracking errors caused (assuming the mount doesn't break, because you're that way over what the mount can carry) blur all of it into a mess, your increased image scale will yield you nothing but heartache.

Look at how many imagers are using a 16" scope on a GEM mount (as opposed to something like a low fork mount). That should tell you something.

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.

Well, then why not change the sensor? It's going to end up cheaper and will give you good results.

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

As far as an EQ6 is concerned, they are NOT lightweight at all. Even a 12" is really pushing that mount, and 100% of the thread respondents that I read up to here are telling you that 14" or 16" isn't sane.

[Ben Ritchie]

I took a look at my 14", and i'm fairly sure you couldn't EQ mount it without major structural work to the OTA - regardless of what mount you have. The OTA's not rigid enough for anything other than a Dob mounting.

[Moonshane]

I know nothing about imaging but I suspect that for the price of the 14-16" dob/EQ6 combo you could get a good mount, a smallish refractor and a CCD camera AS WELL AS a decent dob - maybe 10"-12" - to do some visual while your imaging system is whirring away.

[GrantEb]

Michael

Have you had a look at the Skywatcher MN190? You'll prob be first in SA with one of those.

Cheers

[michael.h.f.wilkinson]

I have to agree with others that a 16" on an EQ6 is a nightmare. The maximum load capacity is about 20 kg, and a 12" newt already tops that (22 kg for the explorer 300 I am told). As weights scale roughly with the cube of the diameter, this yields a weight of 52 kg for a 16" (from a back-of-the-envelope calculation). The mount will break or bend.

[lukebl]

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

I think the answer to that question is clearly a resounding NO, NO, NO!

The upside is that for the same cost, you really can afford a much more practical and effective imaging system, perhaps with enough left over for another scope for purely visual observing whilst the other scope is busy imaging!

[astroimpulse]

This is how I see it:

1: You buy the 16" scope as you clearly want it.

2: It arrives and you're like a kid at Christmas.

3: Your excitement goes through the roof as you open the huge box and see what's inside.

4: You can barely contain yourself as you lift it (with difficultly) out of the box and see it's awesome size.

5: You lift it on to your EQ6 with a struggle. Your excitement is still there but you think "boy, this is tough. It's going to be a pain doing this each time".

6: You move the EQ6 with the scope attached. You're heart drops, like a loved one has just dumped you, as you 'hear' the EQ6 struggle with the OTA.

7: Realising the expensive mistake you have just made you wish you'd listened to the folks in the know on SGL

[Rossco72]

Here's the size of the 14". As has been said, it is big and heavy

http://stargazerslounge.com/members/rossco72-albums-dobsonian-picture7203-me-aaron-new-kit.html

[simon84]

If you even attempted to pop a 16" scope on an NEQ6 it would probably simply just break before even trying to fire it up.

With the 12" the four 5kg counterweights need to be an extra 130mm away from the mount. I hate to think how many counterweights you would need and in saying that the bend on the counterweight bar from 4 weights is considerable, anymore and it will either just snap or blow up inside the mount.

If you ever got it up there you would never balance it, I cant balance my 12" anymore and all because its had a heavier focuser put on it. Thats without putting my 800 gramme EP in there.

Honestly if you really want to mount a 16" Newt on an EQ mount you'd probably be better off strapping it to the side of a cement mixer.

[astroimpulse]

Honestly if you really want to mount a 16" Newt on an EQ mount you'd probably be better off strapping it to the side of a cement mixer.

Sy checks his cement mixer....IT'S A GOER!

[Gary Parkerson]

The old-school rule of thumb was that the telescope mounting should weigh 4 times as much as the OTA and that the RA gear should be of the same diameter as the objective. Of course, modern metallurgy and engineering have superseded those guidelines, but I have still seen only one successful scope+mount assembly in which the payload actually outweighed the mount and that was using the very unique Chronosmount harmonic drive system - a system that does not require counterweights.

Meade once produced a 16" Newt/GEM combination in which the mount featured 1.5" solid-steel shafts and weight of about twice that of the OTA...and that mount was still insufficient for the payload. As others here have politely cautioned, I would not try loading a 16" Skywatcher on an EQ6 on a bet! If that kind of aperture is your goal, you'll be far better served, as others have again already suggested, matching a Dobsonian to a high-quality dual-axis equatorial platform. Another SGL member has done exactly that and is producing stunning images with that combination.

Best of luck.

Gary

[daz]

What is interesting is so many people sitting on the fence here!

[GazOC]

What is interesting is so many people sitting on the fence here!

I'd sit anywhere as long as it wasn't within tipping distance of the scope...