Back in the "dob mob" again .....

[John]

I just wanted to post a few, rather hastily taken, photos of my old-but-new-to-me 12" dobsonian

The optical tube is an Orion Optics 300mm F/5.3 SPX which, according to the optical test, contains a primary mirror with a strehl rating of .987. The optics are from 2005 but were re-coated by Orion Optics in 2010 with Hilux coatings.

The mount has been made for me by fellow SGL'er Shane (Moonshane) and a wonderful job he has done on it

My pics tonight don't do it justice but the mount is constructed from Baltic ply with glued and strengthened joints all round. It's colour has been stained to dark walnut with multi coatings to give it a really professional eggshell finish. The alt and azimuth bearings include teflon pads riding against a material very like ebonystar but a little smoother. The design is Shanes based loosely on the Orion Optics compact dob mounts. It's made to my specs re: eyepiece height, balance point etc. The motions are very smooth indeed on both axis but the large altitude bearings (wagon wheels !) give just enough resistance to enable heavy accessories to be used without needing counterweighting.

I'm absolutely delighted with the mount and scope - it's a "proper job" as we say in the South West

My last 12" dob was a Meade Lightbridge which weighed around 85 lbs. This one weighs around 57 lbs and I can lift the whole lot in one go if needed. Thats about as portable as a 12" scope gets I reckon.

Needless to say it's 95% cloudy tonight and I've only been able to glimpse Polaris a few times to align the finders and check the collimation is there or thereabouts.

Can't wait for a proper first light opportunity of course

Thanks again Shane - you are a real craftsman mate !

[Moonshane]

welcome back John! I am so pleased you like the new mount.

[rory]

firstly ,can i say that looks the biz. very professional looking . i wish i had the skill to make ...stuff !

secondly,ive not seen veins like those before , the two circles . does that let more light pass ?

[Moonshane]

hi John

one thing about OOUK tubes is that there's not much gap between the mirror edge and the tube wall. I see you are using the usual 50mm extension and (assuming the scope is rough at focus point) the drawtube looks like it might intrude into the light path. if you have the back focus available with your eyepieces you might find a 35mm extension will allow the drawtube to come right out of the path. just a thought, although you might be fine of course if the focus position is a little more out than shown.

[Scott]

looks the business. lucky you.

Scott

[JamesF]

Looks very nice And if the weather forecast holds you should be able to get some decent use out of it this evening.

James

[Mike73]

Proper job indeed!!

The biggest gripe I had with my old 12" Skywatcher was with the Alt/Azi bearings.

At low elevations swapping from a 26mm T5 to a Delos caused some balance problems and I never really got on with the wixey Azi bearings as they always seemed to have a wobble and any kind of breeze made for some pretty unsteady viewing!

You can see that Shane has thought about this in his base, I bet its buttery smooth!

I think the dob base really is the weak link with the Meade's/ SW's and although the OOUK base certainly looks like its fixed the problems it comes at a price, if I had the skills to make a good dob base then I think there could be a market for people wanting to upgrade their Chinese dobs (hint hint Shane ).

Weather looks ok for tonight John, lets hope it gets its first light.

[SnakeyJ]

Hi John,

Nice looking bit of kit and Shane has done a wonderful job on the mount - the weight saving over the Meade Lightbridge will make this a whole load more portable which will be a great bonus. Is the figure of 8 spider a standard Orion Optics issue or third party upgrade?

Look forward to your first light on this - lets hope the clear weather holds out for tonight.

Good luck - Jake

[Mike73]

One other thing...... your primary has a very good strehl rating of .987 which is very smooth, if you put your 12" next to a standard 14" Meade/SW I wonder how much (if any) difference you'd see??

[John]

Thanks for the feedback folks

On the spider vanes, the curved design is supposed to eliminate diffraction spikes. From what I've read diffraction will still be present but spread more evenly. We will see

Point noted on the focuser extension Shane. I'll do some experiments on the 1st clear night and invest in a shorter one if needed to keep the end of the focus tube out of the light path as far as possible. I will also make a lightweight light / dew shield for the top of the tube.

As to how the figure / polish of the mirror and the Hilux coatings translate into performance, again the acid test will be using it !

[Mark at Beaufort]

That looks really impressive John and Shane has made a great job on the mount. At this rate Shane maybe going into production .

Well it looks clear for tonight so hopefully you will get your chance to give it a test run. I certainly will be interested how much of an improvement this will be over your previous 10" scope.

Mark

[nightfisher]

Very nice John, Shane is getting the hanh of making dob stuff, looking at the weather forcast my scope is going to be out tonight, could be a good clear night to test it out

[John]

Thanks Mark - I hope to bring the scope to SGL8 and get the benefit of some darker skies

Very nice John, Shane is getting the hanh of making dob stuff, looking at the weather forcast my scope is going to be out tonight, could be a good clear night to test it out

It's looking good here to Jules although it's been so changeable recently I've learned not to raise my expectations too much !.

[Marki]

At this rate Shane maybe going into production .

Mark

A full run of production Shanes? Now that's a scary thought .

Looks like an most excellent scope/mount, John. Had a look at some of Shane's handiwork at PSP - very impressive! Hope you'll have first light tonight - looking promising here!

[moogoomonkey]

Those are some funky secondary supports!

[cotterless45]

Neat, just love these big solid tubes. Hope we all get some clear skies,

Nick.

[John]

Clear tonight.

Wow ! - this is a good scope

454x on Jupiter and lots of contrast and detail. E & F Trapezium just soooo obvious - now for G & E !

Shane - even at the above power the mount dampens vibration in just a second at most - it's brilliant

[Matthew]

Optically this scope is very similar to my old OO dob the views will blow you away john

[estwing]

super scope there John with great results..and well done shane..your getting rather good at this woodwork lark..

[scarp15]

Great collaboration, achieving a superb end product.

[Angus Wright]

John, I was interested to see your scope and hear your report as I am looking at the possibility of getting a similar instrument. I was especially interested to hear you observed Jupiter at 454x as I have an eyepiece that would give the same magnification on your scope, a 3.5mm 82° fov. I was wondering how fast Jupiter would move at that magnification and how often you had to nudge the scope to observe. I know a dob like this is not the ideal scope for planetary viewing and I would mainly be buying it for deep sky observing at much lower magnifications but I'm interested in what it can do.

[John]

Hi Angus,

I've only had one nights observing with the scope so far so it's early days

The optical report with the scope shows that the primary mirror is a good one and with the relatively small secondary obstruction of 21% so I was hoping that it would show the planets and moon nicely and capture enough light to show deep sky objects well.

The ability to use high magnification is also dependent on the seeing conditions and the night I observed was quite good so I pressed on all the power I could, mainly for fun. I'd not usually use that sort of power on Jupiter as 250x is really quite adequate and the contrast and detail is sharper and more distinct at that lower power.

Yes, Jupiter did move rather quickly across the field of view at 454x ! - I was using a Pentax XW 3.5mm which has a 70 degree field of view so it was relatively easy to track the planet but I had to concentrate. My regular high power eyepieces vary from 100 to 70 degrees as my scopes are all undriven and the wider field of view does make keeping an object in view easier

I've used undriven, alt-azimuth mounted scopes for years now so I'm well used to tracking objects with them. I've even managed it with narrower field of view orthoscopic and supermonocentric eyepieces - you just need to concentrate a bit harder

[paul mc c]

Looks good,good work Shane,my scope is the same as yours John and i use 9mm,7mm and ocasionally a 6mm orthos on planets and the views i get are amazing which make up for the norrow field of view which you get used to very quickly.On good nights i have seen detail with in the GRS,and Jupiters moons as tiny discs,to name a few.

[John]

Looks good,good work Shane,my scope is the same as yours John and i use 9mm,7mm and ocasionally a 6mm orthos on planets and the views i get are amazing which make up for the norrow field of view which you get used to very quickly.On good nights i have seen detail with in the GRS,and Jupiters moons as tiny discs,to name a few.

Thats impressive !

Do you use the cooling fan behind the primary mirror with your scope, and if so, what difference do you find it makes ?

[paul mc c]

I always have the scope in the garage,so it's cool down time is quick so i dont use the fan much in cold weather,but would use it in summer more,tho not while observing as it causes vibrations,

and to be honest i dont see much of a difference when using it.

Another example of what this telescope can do is seeing the rille inside the Alpine Vally which is less than 1km wide,give it a go.