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20inch Dobsonian Construction

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sure is damian.

Will be putting the next one on soon although I'm struggling with the secondary holder at present so not quite there.

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Hi Chaps. Thanks Damian for reading my post again. Ive not had much luck with the weather the last 4 months. only got about 2 nights in in the time. so im hoping for some clear nights over the next week. 

im always tinkering with the scope, Finally got a kendrick secondary heater installed. One thing im very proud of is every time i set up the collimation is almost bang on every time. even when i mix the poles up. i put the laser collimator in and turn it on the laser is almost bang on. ohh the satisfaction hahaha.  

im not much of a photographer and i only have a smart phone but with a 20 inch the results are rather exciting. 





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Well done on the shots Pete they look stunning.

I've had another read although I think Mike has been gathering ideas before building his 20"

Still on with mine it's nearly there


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OK so I finally got a Coma corrector for this scope. Most of the correctors require a fair bit of inward travel which this scope hasn't got and I didn't want to cut the poles down so I did a bit of research and found the Baader MPCC mk 3 kit. This comes completely apart and has verious spacers with it so it can be screwed to the back of any 2 inch eyepiece and slots in the focuser like a filter would.

This works really well. A good test is the double Cluster in Perseus. With my low power eyepiece (24mm/30mm 82° ES) each part of the cluster is on either edge of the field of view. There was a little bit of blurred curviture at the last 5% of the field of view but I can definitely cope with that. This morning I viewed Jupiter. Moving the scope so that Jupiter was out of view. I watched it come in to the field of view and as before just the first 5% was slightly blurred but the rest was as sharp as the center. Once again I'm buzzing. The moon was lovely in my ES24

Lovely hubby


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Interesting update Pete about the focus needing more inward travel?

I've gone for the sips system from starlight instrument and it actually added about 40mm to the focal length.

Because the mounting points are welded on for the poles I built a temporary wooden frame to the focal length of the mirror and tested it to make sure.

When testing at the calculated focal point I had racked the focuser all the way out with the 21mm eyepiece and then had to pull the eyepiece out slightly to get focus.

After adding the 40mm it came into focus about 5mm out from the fully racked in point.

It sounds to work well though

Edited by mapstar
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On 01/04/2015 at 18:56, astrolunartick said:

Here's a little up date. I got the holes drilled in the poles for the Secondary cage and also the threaded inserts (star nuts) pushed in to the end of the poles. I love using large heat shrink around poles to give a nice matt black finish and gives a durable cover. I have used this on other scopes and projects many times and found it very hard wearing and looks great. 





hi, just wondered were you got the star nuts from any links. thanks

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