16" f4 Orion Optics UK Dobsonian Project

[Moonshane]

The installed mirror looks fantastic and really makes the cell come to life. Great job.

The clearance around the primary is very tight as you say. D'you think this will affect the image using wide field eyepieces? I read on another thread (the octagonal wooden tube build if I recall correctly), that you can get vignetting if the tube is too close to the primary when viewing very wide fields. May be more of a theoretical issue than in reality, but what d'you think?

Really looking forward to seeing the base built. Keep going mate, nearly there.

cheers Kevin.

not sure about the clearance vs wide field vignetting issue. I tend to rely on the fact that OOUK presumably know what they are doing.

I am trialling this solid tube this season and will see how it feels and how much hassle it is compared to what I think a truss version would be like.

I may make a truss version next summer and then do the same. the good thing is I have designed this one specifically with that in mind, so I'd just need to make a secondary cage, and mirror box (and come up with a way this time to fit a round cell in a square box!), and use the existing base and alt bearings. then I'll have a choice of two options I suppose.

[Moonshane]

If you install a fan on the cell, how effective d'you think it will be? You've a wacking big chunk of glass in the way and there's not much clearance to create air movement - you may find it doesn't draw air through the tube at all. Could you install in the side of the tube above the primary?

I could try the fan above the primary but don't think this will work too well if the mirror is not already cool. with other scopes I have left the end cap on and the focuser open and this creates quite a draw of air up the tube.

I will of course fit a baffle around the fan to ensure it does not recirculate the same air.

I'll play it by ear, adding the easier mods first. again observing at lower powers in the main will help with this of course.

[Moonshane]

hi all

yesterday I cut the basic shapes for my base and glued them up overnight. I made the two sides and the base board, cutting the curves matching the alt bearings. the bottom board was 12mm plywood x 2 making a 24mm thickness. the sides matched the alt bearings and had 18mm plus 12mm plywood sheet giving 30mm thickness.

today I sanded the sides to identical shape (or as near as possible) and then made some cut-outs to reduce weight, worked well.

I should manage to get the base glued and screwed tomorrow and also make the ground board, and perhaps also glue in place the various bearing surfaces. if things go well tomorrow, I may even get first light on Sunday if it's clear.

I can then paint the base and alt bearings during the next week or so and fit the fan.

I'll post some pics when I get a chance.

[spaceboy]

Where's the pic's

Have you weighed it ? Sounds like it's going to be a heavy weight.

[Moonshane]

not took any yet - will do when the base is glued and screwed etc. I think the base will be about 40 pounds and the OTA about 60 pounds max so not too bad.

[Moonshane]

guess what's collimated and cooling outside!

I have not had chance to take pics but will document what I did and post asap.

the bearings are nice and smooth but might need to give the azimuth one some assistance as it's a bit heavy. I think a further teflon pad in the centre will work fine although I'll try some wax first.

still needs painting obviously but it looks good.

[John]

What will your 1st light object be Shane ?

M13 would be superb - but it's your call of course as you built it

[Glen]

Blimey Shane, you don't hang about! How did you get on?!?

+1 for picy's, bet it'll look super on the base

[yesyes]

Yeah, pictures please, even if it's not finished... ;-)

[Astrokev]

....keeping us in suspense for the big reveal !

[Astro Imp]

Come on Shane, first light report please.

[yesyes]

I bet he was rendered speechless by the views... ;-))

[Glen]

I bet he was rendered speechless by the views... ;-))

[Moonshane]

hi all

sorry for the suspense! I was out until 2.30am last night and on a school night too.

all I can say is WOW.

there are some teething issues to sort out - aren't there always with a new build? - but in most cases these can easily be overcome although one will be slightly tricky.

cannot spend long on this as I have spent a few days on this to get it sorted but here's a run down of what I have done:

• created sides for base with 12mm and 18mm ply bonded together.
  
• this 30mm matched the alt bearings.
  
• I gauged the height using pythagoras and to give me some latitude to raise or drop the tube if required.
  
• this resulted in a focuser height at my own eye height roughly at the zenith for comfortable observing.
  
• made some cut outs to reduce weight and provide a grabbing point to carry the base and also added some 'keeps' to prevent lateral movement.
  
• made the bottom board out of 2 sheets of 12mm ply bonded
  
• made a front panel which was glued and screwed with the rest of the base. I thought about a cutout here too but it was not really going to save any weight and seemed pointless.
  
• I will add the back panel/possibly corner wedges in due course when I know the minimum height of the tube.
  
• then created the ground board. a simple circle of 530mm, three feet, glued and screwed and then some rubber pads glued on with impact adhesive. on the top, some teflon pads again etched on one side to allow impact adhesive to be used.
  
• subsequent use confirmed that a similar sized teflon pad was required around the centre bolt and this along with turtle wax on the laminate works wonderfully well.
  
• impact adhesive used the glue on the formica to the alt bearings and the base.
  
• all held together with a M10 cap head bolt and a locking nut welded to a plate.
  
• I also then glued the teflon pads onto the upper surface of the curves on the sides of the base.
  

Obviously it needs a fill, sand and paint (satin black) but will be excellent to use, I can tell that already.

pics of all this below.

teething troubles:

1) I knew I may have to tweak the focuser etc but I was rather shocked that focus on eyepieces was around 30-40mm short. Luckily I had a low profile focuser from an Intes MN68 and quickly swapped over this for the original focuser. I could then use my TV eyepieces but not the BGOs as these use a lot more in focus. I could not get anywhere near the Paracorr's focus point. So I need to move the mirror up the tube by about 50mm I think to get the required focus point on all eyepieces with the Paracorr. I can use the current holes as a starting point and carefully measure up the tube by the correct distance once I calculate what this is. At least I got to use the scope for a first light on the day I completed the build and the coma whilst obvious on the scope, was actually not as bad as I anticipated.

2) The movement was initially quite stiff and sticky but after the changes to the bearings referred to above, it now works like a buttery dream.

3) Tube slip - the tube is quite heavy (about 60-70 pounds) and tends to slip down even though I have a further 'anti slip ring' in place. I will presumably have to like the rings with a further layer of something a little less slippy than felt to prevent this. Perhaps some 2mm 'funky foam' of which I have a little left. Again an easy fix.

4) Shane's knobs too short - I will have to make some more secondary adjusters with a longer thread on them - an easy fix and I have the bits.

Other than this I am truly delighted with the way it works and gathers light. Here's a brief snippet of the highlights in no particular order (as they say on the X Factor - so I'm told ):

Globulars

M13 - had to be first. Stunning and stars resolved right down to the bone, propeller obvious. M92, surprisingly bright and beautiful. M2 was really fantastic, incredibly bright and resolved stars a long way in. M72 was very faint even in this scope and quite low in elevation but really pleased to see this for the first time.

Galaxies

Only M31 et al were available in terms of main galaxies but these were the best views I have had of M31 and M32 from home. Really bright and extended, a hint of dark dust lanes and even managed to see M110 for the first time from home - superb!

I also saw the small NGC companion galaxy to M13, cannot recall the name - will look it up shortly. Again for the first time.

Nebulae

The Ring M57 and Dumbbell M27 were obvious targets and did not disappoint. Superb brightness and contrast for a light polluted site.

Open Clusters

M39 in Cygnus was brilliant as always as was the double cluster in Perseus. M73, seen for the first time was a little pathetic after seeing the other delights of the night but good to get another (probably the worst) new messier.

Supernovae

With Cygnus right overhead and the Oiii filter in, I could not resist a look at the veil. The witches broom and the bridal veil were much more obvious than at home previously with the 12" and no need to look for them at all. if my neighbour had not been switching their kitchen light on and off all night, I'd have probably seen detail. I then tried without the filter and given this is a light polluted area, was amazed to see traces of the veil, especially the bridal veil, in the eyepiece unfiltered.

Planets/Moon

As I was getting to the end of the night with the moon up, I took a look at Luna and the view was really good given it was unfiltered and the moon low in elevation. Looking forward to more looks at the moon with this scope.

I found Neptune too in Aquarius although could not detect Triton. Perhaps as Neptune was virtually in the trees, low down, above houses and with the seeing quite poor, this is not surprising. I'll take another look towards opposition in August (?).

Jupiter was just peeping over the rooftops so I had a quick look but it was a poor image given the same kind of circumstances as Neptune so I had a quick look, noted the two main belts and planets of course and then packed up. What a great night visiting lots of old friends and some new ones with my best scoping buddy.

This scope will be truly spectacular at a dark site I think.

Cheers for all your support everyone and I will continue to add updates as I paint the base etc and get the focus point sorted out. I'd really like to be able to use the dual speed crayford I bought for the scope if it can be sorted out.

BTW the eyepiece in the scope is a 26mm Nagler - looks more like a 24mm Panoptic!

[NGC 1502]

Hi Shane, very well done, bet you will get lots of great nights

Clive ( the one you got the mirror & tube from ) has got his 17.5" back from refiguring and recoating. When he collected it from Galvoptics he called on me, as they are only 10 miles away from me in Basildon ( I'm in Southend ) Still waiting for a first light report.

His scope is done, he was able to try it with the old dodgy coating before it went to be worked on. We will both be at Kelling in Sept, so hoping for a butchers through it

Thanks for all the posts, been following this with interest, Ed.

[Moonshane]

cheers Ed! I am so glad that Clive got his sorted. I bet that the 17.5" f5 (?) with 1/10PV optics will be just awesome.

I have to say that I am going to have to make a buggy/bogey or some barrow handles for the scope. I have enough spare ply, carrying it the length of the house and outside is no fun. up onto the mount and into the car will be OK, but carrying any distance is another matter. just need to find a supplier of small, cheap pneumatic tyres.

[Astrokev]

Looks great Shane - a big well done from me! Look forward to seeing it painted.

[Moonshane]

cheers Kevin. me too!

I will give it a rest for a few days but will at least start the painting this weekend to at least undercoat stage, possibly more. might be able to borrow a spray gun.

[NGC 1502]

Hi Shane, yes, Clives scope should be the biz, cost him for the refigure & recoat, but he will be well rewarded with some great deep sky views. He has made a truss tube

Dob, with octagonal mirror box and secondary housing from plywood, looks great.

When I first knew Clive and he got the 16", he lived in a second floor flat. He used a

sack barrow to take the tube down in the lift. When he got back home, he was always worried the lift may have broken..........Thank goodness he now lives in a house with a back garden !

Good luck with the mods you have still to do, icing on the cake ! ..........Ed.

[Moonshane]

cracking thinking Ed. a sack truck would be the business, and I could also use the excuse that it's not astro gear too as it's useful when moving house etc - my mother in law seems to move at least once per year!

[Glen]

Teething aside as it's expected on a venture like this, it's great to read your first light!

I bet you was like a little kid again...gotta look at this, and that and ..and..

Still when it is finished ( yesterday, at your rate ) it'll give you years of fantastic views, and one to watch out for at the star parties?!?

Thanks for the updates

[Moonshane]

cheers Glen - just looking at cans of spray paint as an option as it's much easier than using a gun I suspect to a novice but then again, might be just as easy with a spray gun and compressor with a quick lesson first.

looking forward to getting it used again at a dark site - have one lined up on private land which will be a treat.

[Glen]

It's been said before, but maybe think about taking it to the local body shop, after all whats 3-4 possibly 5 cans of paint gonna cost?

just a thought fella

[johninderby]

Great job Shane

Just a little bit different now compared to the state I saw it in when you'd just collected it. At least the few initial first light problems sound like they're just really of the "fine tuning" sort, and I'm sure you'll soon have it spot on.

Look forward to seeing pics of the fully finished (painted) scope.

John

[yesyes]

I would paint it myself. Having it spray painted doesn't quite have that DIY factor.

You wouldn't want to look at it and think "I built that; apart from the painting."