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Posted (edited)

One of the issues I have found when searching for targets with my 8"dob is making small adjustments. At the minute the only way to move the scope is by grabbing the end and pulling/pushing the tube but this either results in it going to far or jumping.

Even if I aim the telrad in the area where I think the target is, when I look through the ep then start scanning it is tough to do a thorough search.

Anyone got any methods for finessing the scopes movements?

Edited by popeye85

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Have you got a "dob knob" fitted to your scope ?. It helps with moving the scope smoothly.

image.png.8d779d14ac8069d26a9cdf93f3e6708d.png

 

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You could try silicon spray on your alt and Az bearings and make sure that the scope is balanced.

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Posted (edited)

 
A few ideas to try, best if you’re a DIY type......

To make the altitude movements easier, the teflon pads can be moved a bit closer together.  Experimenting is needed...if they are too close then changing eyepieces can cause the tube to tip.  To help the azimuth movement, if the 3 teflon pads are a bit nearer the centre bearing that can make the movement less stiff. Or there’s the old trick of adding thin plastic washers around the centre bolt   - made from the side of a milk carton - not enough added makes no difference, too much and the scope teeters on the too high centre bearing, needs to be just right to work.    Or instead of teflon pads, a “lazy susan” bearing could be ok....

I love Dobs, but a sticky Dob is a big pain, a smooth Dob is an absolute joy to use....so it’s well worthwhile getting it right.

Good luck, Ed.

 

 

Edited by NGC 1502
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Unfortunately I have said this several posts most people disagree with me it's even worse at high powers 200x to 300x.

That's why i prefer eq mounted even if it doesnt have any drive just the manual slow motion controls is much better to use then push pull system of our hands.

Getting those dob drive bases can be done but for me $600 costs can be as much as the whole scope. Ie the skywatcher 10 inch dob is on sale for $719

If i use a dob i norm use low to med to medium-high powers after that it's too tricking tracking by hand.

Of course the expensive dobs may be alot smother than the regular mass produced dobs.

Joejaguar 

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I mean I even once replaced the regular teflon pads on both axis with virgin teflon which is more smoother, based on a book I read in the mid 90s. It did help a little bit on my 16 inch dob but still had same issues. 

Joejaguar 

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My 12 inch dob has smooth tracking on both axis. Just teflon pads but in the right places and running against a suitable laminate surface. No problem tracking at 300x or more (as I have been tonight).

Getting the axis to move smoothly is the key and well worth the effort.

 

 

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popeye have a read at this thread I think it may be what you are looking for. 

Jim 

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Maybe I'm very lucky.

I have the lowly, but popular Skywatcher 200p and it moves just fine.

I haven't modded the Dobsonian mount at all.

I was quite careful when assembling initially for things to be just right, not to tight or too lose, but other than that, it is how it came out of the box.

I star hop at low magnification before spiralling in on the target and then adding some magnification.

I nudge rather than track, but find it effective enough for me.

I've enjoyed the moon at silly magnifications with no problem.

I was lucky enough to find parts of the Veil Nebula this Autumn for the first time too.

Maybe you need to consider stripping the mount down and seeing if there is any way of making it move smoothly.

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Replacing the az bearing with a roller bearing will help a lot.

https://www.teleskop-express.de/shop/product_info.php/info/p1646_Azimut-Roller-Bearing-for-Dobsonian-Teleskopes-D---320mm.html

The lazy susan aproach is a lot cheaper but requires adding some riction to the movement to stop the scope just spinning at theslightest touch.

You could also replace the alt bearing with a friction bearing.

https://www.teleskop-express.de/shop/product_info.php/info/p6767_TS-Optics-Friction-bearing-for-altitude-axis---for-ATM-mount-and-Dobsonian-construction.html

There are a lot of threads on low cost modding your dob so do a search if you don’t mind a bit of DIY. Adding a handle or knob at the top end of the scope makes it much easier to control.

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I notice that the OP's dob is a Revelation 8 inch. I thought those had lazy susan type roller bearings to the azimuth axis fitted as a stock item ?

 

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I used the milk carton solution on the central bolt for smoothening the az axis of my SW 8" dob. It works well.

Off topic, but something similar can be done to improve the movement of the thumb screws adjusting the secondary mirror.

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Posted (edited)

I can confirm the Revelations do have the Lazy Susan bearing by default. One issue is making sure the base is level - if it is the Az action is smooth and can be a problem with the wind moving it like a sail. If not level then it can stick quite badly. With mine the Alt motion is rather too free (probably needs new hold-down springs as it is rather ancient). I use some magnetic welding weights to adjust the front to back balance depending on where I am point it.

Edited by IanL
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Thanks for all the responses folks!  Will have a look at the lazy Susan and make sure that's it's running as it should be as that does feel like it might be one of the issues.

Some sort of slow motion control would also be a great assistance in slewing the scope. @fiestazetecmk2 set up looks like just the job but a bit too advanced a project for a non DIY we like me! Open to other (basic) options along the same thread though!!

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Posted (edited)

One problem with the Revelation az roller setup that can occur is if it is greased which can stop the rollers from turning properly. Just WD40 or something similar sprayed on and wiped off is all it needs.  

Edited by johninderby

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The Revelation 8" dob (I have one) has an adjusting bolt in the centre of the base under the body of the scope.  It is possible that this is too tight and needs to be loosened a little. 

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I had a similar problem with a sticky altitude bearing.  @brantuk gave me a tip to use a strip of the loop side of velcro on the base bearing of my dob.  Perfect mix of free movement and “stiction”.

You might also consider an equatorial platform at some point.  It holds your target in place and reduces the amount of fine adjustment needed.

John

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