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20inch Dobsonian Construction


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Ive not been on here in a long time and all my details and posts have sadly vanished so ive got to start from scratch. 

Ive been planing a larger 20 inch dob for some time and finally have the funds to do it. ive already made two 4.5 inch a 8 inch and three 10 inch dobs so i have a little experience.

I bought David Kriege and Richard Berry's Book The Dobsonian Telescope ( a practical manual for building Large Aperture Telescope)

I highly recommend it. Its a fantastic book. I would say its all you need if you what to build a Dobsonian.

Ive gradually been collecting the parts for the dob. Ive order a 20 inch F4.2 for John Nichol at Nichol Optical. It should be with me within the next few weeks

I got my hands on a CR2 Moonlite focuser.    also ive got all the little bits like teflon Laminate edging. nuts and bolts ETC....

Just waiting for the mirrors and then i will order the birch plywood and Aluminium poles

So fingers crossed all will go well and ile post up my progress soon. 

thanks for reading. 


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Hi Pete.

I built my 20" following that book and taking a little inspiration from Eric Websters awesome scopes.

Have fun. I look forward to following your build :)

Ps Nichol optics. ;) great choice. John is a true perfectionist and a real gent.

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.  whats the focal length of your 20 inch? Pleased to here your happy with John Nichols optics. so far i found him very friendly and helpful.

Mines f/4 can't remember the exact length but it's around 80". I did do a build thread somewhere on here.

:iamwithstupid: can't seem to find it though.

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i think ive seen it. i will look again.  Do you need a coma corrector with you Naglers on the f4 20inch? I have a skywatcher coma corrector i was wondering if i will need it. on my f4.2 when its made

This is personal choice really. Olly doesn't use a CC on his 20" (f/4.1 I think). I do. :)

I have the feathertouch SIPS system on my scope, IMO this is just superb. It combines paracor and Feathertouch focuser. It cleans all the big wides right up.

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Hi Pete,

 they say anything shorter then an  F- 4.5 should have a CC, you can try it with and without to see the difference,

I am hoping to have my mirror finished before spring and then start construction as well but currently on break with

injured wrist, looking forward to reading your construction notes so please post a plenty, keep us updated.

Rick M

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Hello again Scopers

Here is my first update on my 20 inch Dobsonian build.

As of yet I've not touched my tools. Im just waiting for the the mirrors and a few bits and then i will take a trip to the timber yard to get the Birch plywood

Today the Aluminium Poles and the Aluminium parts for the Mirror cell arrived and also some bendy 3mm Birch plywood for the Secondary cage arrived at work.

Here is a photo of the Moonlite focuser, Telrad and other bits and bobs.

Its all rather exciting and im hoping every arrives OK fingers crossed.


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Geez Mate,

With Swamp Thing, Faulksy, Estwing and Simonfromsussex following this thread, you better not make any mistakes :D.

Good luck and look forward to your progress

Those Guys have made some impressive scopes. So the pressure is on. I have a workshop half built and what with work im not sure how soon i can commence with the project.

It probably will be soon as im to excited to look through the finished scope.

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I have a Question in regards to the mirror cell. In this book im reading (The Dobsonian Telescope a practical manual for building Large Aperture Telescope)

It suggests building each pivot point or each balancing point of the Mirror cell with nuts and bolts loosened so they rock in to equilibrium as they put it.

I was wondering how effective this is. Obviously Dave Kriege has been building his scopes like this for years like this.

The reason I have been wondering this is because I have seen some mirror cells made with Rod end bearings. I thought this was a good way of constructing a mirror cell but I Maybe wrong.

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