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Anyone in NW England with an 18" dob?


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Hi all

I am beginning to finally submit to aperture fever and think that an 18" f4.5-4.75 mirror in my home made lightweight truss dob is the way to go. BUT I would really like to 1) have a look through one to compare it with my 12" 2) see how big they really are and 3) make sure it really is what I want before I spend the cash on the mirrors.

I intend to actually make the scope before I buy the mirrors as this will be relatively inexpensive and I can then gauge the size, whether it will fit through doors etc and it gives me lots of time to actually complete the construction/manufacture rather than rushing it 'cos the mirror is sat there staring at me.

So, is there anyone locally to me (Manchester/Stockport etc) that has a large dob of this sort of size (16-18") that would be willing to meet up (I can bring my do to you) and 'compare notes'?

Cheers

Shane

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At 18" you will start to hit door trouble unless you are careful the design. The size and weight depend on the focal length you choos, a shorter one would be easier to use but need a paracorr to keep the coma at bay. The 12" is big but what you're planning is definitely worth sizing up. Done right it could be no harder than your 12".

PEterW

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cheers Peter

I was initially thinking a 16" but as you say, if I design it well then I should be OK.

The idea I have in mind is something like the Obsession Telescopes / Telescopes / 18" UC (Ultra Compact) but perhaps at a shade or two over f4.5 and hopefully within an overall budget of £2500. This will put the EP at just over my standing height at the Zenith but not much so may just need a box to stand on (at 6'3"). This will possibly avoid the need for a Paracorr.

I am really itching to get going (and will of course start a thread) but I want to make sure I research properly and get it right.

Edited by Moonshane
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Hi Shane

The thought of a 18" dob sounds very tasty your doing the right

thing with taking your time & planning

but with AP fever i guess its not easy :)

those 18" UC dobs on the O T site look really good

clear skies

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Well done on your decision Shane. I don't think you'll regret it (provided you are strong enough to lift the mirror box !).

Just a word of caution; If you intend to construct the mirror cell, ensure you have the precise diameter of the mirror beforehand. When I rang the firm making my 350mm mirror I was told it was 14 inches, ie. 5.6 mm more). Luckily I delayed mirror-cell construction until receipt of the mirror before beginning.

How exciting, wish I was in your shoes.:)

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Hi Shane

The thought of a 18" dob sounds very tasty your doing the right

thing with taking your time & planning

but with AP fever i guess its not easy :D

those 18" UC dobs on the O T site look really good

clear skies

cheers Kris

I am looking forward to the build as much as getting the mirrors!

I am five steps forward and 4.95 steps back every day with decisions and keep doodling on pads at work etc!

Well done on your decision Shane. I don't think you'll regret it (provided you are strong enough to lift the mirror box !).

Just a word of caution; If you intend to construct the mirror cell, ensure you have the precise diameter of the mirror beforehand. When I rang the firm making my 350mm mirror I was told it was 14 inches, ie. 5.6 mm more). Luckily I delayed mirror-cell construction until receipt of the mirror before beginning.

How exciting, wish I was in your shoes.:)

Cheers Alan - great advice! thanks.

I am lucky that I think I have a mirror which I can take when ready (an 18" f4.7) so I should be able to get measurements before building the cell.

the weight should not be too bad as the mirror is about 32lbs and I'll be using 12mm ply doubled up in places, possibly an ali cell (maybe steel) and I reckon in all I should be able to keep it down to about 50lbs for the mirror box with any luck. I may make some wheelbarrow handles though so it's only a matter of lifting out the back door or into the back of the car.

18 inch dob, that will be a right bit of kit!! good luck

Indeed matey - let's hope it all comes to fruition. one big challenge will be not buying any more goodies of any note for 12 months!

Edited by Moonshane
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I think 18" is a very good compromise between size and portability. You'll be gathering over twice as much light as a 12". That'll make a lot of difference. I'm thinking of upgrading too...

Edited by umadog
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