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Old 29-02-2020, 11:00 PM
Auzzborn (Damien)
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Thinking about buying a GOTO mount

Hi all,

I've owned a 10 inch dob for a few years now, pushing and pulling around the night sky. I'm trying to understand different computerized mounts. My goal is to be able to throw in a 3.5mm eyepiece and gaze the planets for long periods without having to touch my telescope, same goes for 30mm viewing nebulae and everything in between. Will a GOTO mount achieve my goal? How much vibration do the motors cause at the higher magnification?
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Old 01-03-2020, 12:31 AM
raymo
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Provided that the mount you choose is appropriate for the size of scope that you put on it, you will have to perform an alignment procedure, and once that is done a selected target should be within the field of view of a low power eyepiece.
You then centre the target if necessary with the direction buttons.
Once centred the target should stay in view for an extended period of time. [at least 30 mins, but usually longer].
The better the alignment is performed, the longer the target will remain near the centre of the field of view. Even at high powers, using a decent mount, motor vibrations should be pretty much undetectable. If they were, you couldn't do astrophotography. The only time you would see any vibration
would be when slewing from one target to another.
raymo

Last edited by raymo; 01-03-2020 at 12:34 AM. Reason: more text
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Old 01-03-2020, 12:37 AM
Auzzborn (Damien)
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Thanks for your reply, much appreciated!
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Old 01-03-2020, 04:06 AM
Ukastronomer (Jeremy)
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Personally it is impossible to answer your question without stating a price you can afford

The more you pay the better the mount, for a 10" it won't be cheap
.
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Old 01-03-2020, 05:45 AM
Malcolm
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If you have a SkyWatcher dob you can buy a GOTO upgrade mount. The mount must be perfectly level for good alignment and tracking and the simplest way to achieve it is to fit leveling feet which you can get at Bunnings. Three 19mm thick hardwood blocks screwed and glued to the base instead of the rubber feet to accept the threads of the leveling feet. A SynScan WiFi dongle and the SynScan app together with SkySafari pro can be used to align and drive the mount making the handset redundant. An EQ mount, if that's your thinking, is not a good idea for a 10" OTA, the length of the tube will act like a sail in the slightest breeze and the eyepiece often ends up in an awkward position, requiring loosening the tube rings and rotating the tube. If AP is your goal, an EQ mount with a refractor is what you need, if visual only a GOTO dob is fine. I use a 4cyl jumper pack to run my goto dob out in the field, modified with bullet plugs from Jaycar as the cig lighter socket connection is not all that secure. At home a 240v - 12v 2A DC adapter, also with a bullet plug.
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Old 01-03-2020, 08:31 AM
Martin_S
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Damien, I had a SW 8" GOTO dob with starsense for SW . The biggest mistake I made was selling it in haste to upgrade to an EQ mount ETC for astro photography. That setup is about the simplest GOTO you can get .

Martin
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Old 01-03-2020, 11:49 AM
Startrek (Martin)
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I used a GSO 10” push pull dob for 3 years and waisted precious time trying to find objects all night even with using a planetarium visually and star hopping
I now have a Skywatcher 12” Goto dob and can find objects with ease
Once 2 star aligned ( takes 5 minutes ) the Goto is extremely accurate
Last night I observed M42 , NGC 3372 , NGC 2808 and a few others in just over an hour session
And scope is left outside with a tarp over it fully aligned ready for tonight if it’s clear
If you have fun trying to star hop to find objects , that’s fine , but I got to frustrated and now with the Goto it’s exciting observing anywhere between 5 and 10 objects each time I go out

And yes a Goto , aligned properly will keep your object in the centre of the eye piece for a long time before you start to drift
I observed Jupiter and Saturn last winter for an hour before any noticeable drift
Skywatcher Goto is very accurate , level your mount base, set your scope in home position horizontally level roughly pointing true north or south and perform a 2 star alignment using an illuminated reticle eye piece on bright stars on the same side of the meridian about 35 to 60 degrees in Alt and about 50 to 70 degrees apart in Az
That’s it , works for me every time !

Cheers
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Old 01-03-2020, 02:43 PM
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mental4astro (Alexander)
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Hi Damien,

I'm going to suggest something different.

Have you cleaned the alt and az bearings of your dob? This is one of the most basic things that most dob owners forget about, or doesn't occur to them that needs doing.

If you don't, you will find that you need to use more force to move the scope, the action becomes jerky, gittery and vibrates, and it will display a whole lot of backlash because the mount is also flexing because of the additional force.

I have 5 dobs, from 114mm to 17.5", and I clean their bearings once a year and apply wax to the bearing surfaces (not the Teflon!). I have no problem following the planets at 400X, and the eyepieces I use don't have an exceptionally wide apparent field of view. The action of my dobs is silky smooth and I have no backlash with them.

None of my dobs are motorized either, and for a very specific reason - you actually SEE MORE in DSO's with a push-pull dob. It all has to do with the way our eyes work at low levels of light. In low light, the rods and cones in our eyes quickly saturate, and their sensitivity quickly drops. It is by moving the scope that the moving image triggers the refresh mechanism of our eyes, and their maximum sensitivity is restored, and all of a sudden you are once again catching a glimpse of that faint nebulosity that at first you "thought" you saw, but lost with a static image. Moving your head or eyes is not enough - the image itself needs to move. With a go-to scope, you can achieve the same by giving the scope a good tap to induce a vibration, but this is not something people with a go-to scope do with any regularity. You may think the constant nudge-nudge-nudging is a pain, but it works in your favour.

If you post a picture or two of your dob, we will be best able to advise you on how to go about cleaning the bearings of your dob to get it working to its very best again

Another factor that can be working against you is where you set up your scope. Grass, and especially lush turf is the very worst place to set up on. Mass production dobs from SkyWatcher and GSO have stupidly little "feet" made out rubber stops. These are fine if you set up on concrete, compacted earth or some other hard surface. But set up on grass and those ridiculous "feet" cannot reach down through the stuff, and instead the ground board is resting on the grass itself. This then makes the turf a mechanical part of the mount. So when you want to move the scope you need to use greater force because the sponginess of the grass needs to be overcome before the scope will begin to move. And when you release the scope, that sponginess is released too and is seen as backlash. This alone will make trying to follow the planets at high magnification an impossible task. If you can only set up on turf (either because of where you live or because of where you find yourself setting up), there are ways to easily modify the ground board so that turf is no longer a factor

Setting up on turf will also affect the pointing accuracy and mechanical functioning of Go-To dobs (commercially made and custom) if the same necessary steps are not taken.

Grass is also the very worst place to set up a mass production dob on as the evening dew will seep in through the seams of the laminated particleboard mount, causing this cheap stuff to puff up and ruin the mount.

If your dob is one that makes use of a friction clamping device on the altitude bearing, having this wound too tight will also significantly impact on how silky smooth the action is of your dob. These friction devices are a way of overcoming the unbalanced design and manufacture of these dobs. They DO NOT restore balance. But by loosening up these clamps too much, it may leave the scope either top heavy or bum heavy, and it tips over easily. An easy way to help overcome this is by using BIG magnets wrapped in a sock. Depending on what eyepiece you are using, the magnet is moved up or down the length of the OTA to actually restore the balance of the OTA, and the action of the scope is kept both light, smooth and consistent.

There is one other way to extend the drift period of objects in the eyepiece - using EPs with a wider Apparent Field Of View (AFOV). Plossls typically have an AFOV of 52°. Plossls are also a very old eyepiece design (over 150 years actually). Contemporary EP designs have anything from 58° to 100°. Some of these cost more than your dob, but excellent EPs can also be had without killing the piggy bank.

An alternative to Go-To systems for existing dobs

If you want a pointing system to help make your time more productive, instead of an go-to, you might consider a push-to set of digital setting circles, like the Nexus from Astro Devices. These will not only work with your phone, but they won't add any mechanical impedence on the quality of action of the scope so you can retain its full visual impact for your eyes. I can fit 3 of my dobs with the Nexus DSC when I am chasing particularly difficult targets. These Nexus devices can be easily installed onto mass production scopes and also custom made dobs. The Nexus DSC has a catalogue of some 2.5million individual objects. And there is the option of fitting all the Nexus devices with Extreme Encoders. These have a resolution starting from 350,000 steps and up to 1.2million steps. Even at their lower resolution it is possible to identify individual objects within the Small and Large Magellanic Clouds - something that no commercially made goto mount can do. These digital setting circles are also easily fitted to commercially made dobs and also custom made dobs.

Alex.

Last edited by mental4astro; 01-03-2020 at 05:00 PM.
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Old 01-03-2020, 04:24 PM
Auzzborn (Damien)
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Thanks everyone for the detailed information. I'm going to try Alexanders suggestion to clean the bearings first and see if I can get my mount silky smooth, may save some money if I'm happy with the results! I might report back with how it goes.

BTW yes, I have a skywatcher 10" Dob non-collapsible. Eyepieces I currently own Pentax XF 8.5mm & 12mm, the 25mm & 10mm plossl that came with the telescope and a Televue 32mm plossl & 2x Barlow. I want to get the Pentax XW's and Explore scientific 82deg 30mm once I get this mount situation sorted.
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Old 01-03-2020, 07:32 PM
astro744
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If your only goal is tracking then all you need is an equatorial platform also known as a Poncet platform

You can buy these from a number of sources with a wide range of prices or you can make you own with many plans available online. Even Bintel sold the Johnsonian VI model about 15 years ago but this one is no longer made.

To use you simply place your current DOB base on top of the platform and you get about 45min of tracking. To reset the sector takes a matter of seconds. Some EQ platforms become your new base so you first must remove the ground board of your current mount. You need to get one for your latitude. The platform will add about 150mm to your current eyepiece height at zenith and for a 10" f4.7 Dob, this is ideal for an adult.

There are dozens of links if you search for EQ Platforms and also Affordable EQ Platforms. Here's a couple at opposite ends of the price scale. See

https://www.oreilly.com/library/view...4/ch04s21.html

http://www.equatorialplatforms.com
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Old 02-03-2020, 09:10 AM
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mental4astro (Alexander)
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An eq platform is a good option for planets with dobs, astro!

Select or build the right sort of eq platform design, and it will also double up as a decent photo set up too. I had an eq platform for a time, and used it with my 8" f/ dobbie for video astronomy - also one of the dobs I can connect my Nexus unit to.

But I would still suggest first cleaning the bearings of your dob and working with a big magnet and see how you go before laying down any big money. It is the easiest thing to do and will give you immediate results.

The bearing surfaces, clean them only with metho using a cotton cloth. Use a GOOD quality car wax (such as Turtle Wax that comes in a tub - the cheap stuff in a bottle uses solvents and won't give the same long lived finish) on the bearing surfaces. DO NOT apply wax to the Teflon pads - it is the very physical properties of the native Teflon that makes it an excellent bearing material. Put wax on it an it will no longer be the Teflon that is at work. You can clean the Teflon with metho

Alex.
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Old 09-04-2020, 03:28 PM
napster (Jonathan)
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nice
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