Primary way off center... joy, something else to fix

[Dave_D]

So, after yet more hair pulling and leaping about over this damn scope, tonight i found that the primary was so far off center that on one side of the mirror i could barely get my finger tips between the primary ant the tube wall, but on the opposite side i could get my fingers up to the knuckle...

The fixing points of the cell have a good 5-6mm (total) of play between the outer edge of the cell and the inside of the tube. Fortunately, i still have the offcut from when i did the spider, so a bit of work with my dremmel cutter and some wet and dry tomorrow to fashion a ring to fit inside the tube to slightly reduce the inside diameter and give a snug fit to the primary cell. Fingers crossed that this will be the last major mod i have to do... was the orion optics GX250 a bit of a mechanical monstrosity when it was released, or did i just end up with a duff? because the build quality of this one is utter pants.

[Skyline]

make sure the doughnut on the primary is centered, cheap scopes likes of skywatcher sometimes have these problems.

[Dave_D]

make sure the doughnut on the primary is centered, cheap scopes likes of skywatcher sometimes have these problems.

already done that a while ago. don't know if it was the original orion optics centre spot but it was a few mm off true centre. printed my own custom template on acetate to redo it.

[crashtestdummy]

All sounds like familiar critiscisms of OO tbh.there's been at least 3 threads in the last few weeks.it does disprove the get what you pay for ethos.

[Dave_D]

All sounds like familiar critiscisms of OO tbh.there's been at least 3 threads in the last few weeks.it does disprove the get what you pay for ethos.

Well, in all fairness i only paid £400 for the scope and mount and it *is* quite old... optics are fine though, need recoating but that's for another day.

[Dave_D]

the patient is doing well...

[crashtestdummy]

But is it likely that the scope has been *off* since New?

[Dave_D]

i don't know, from what the guy i bought it off said, i'm either the 3rd or 4th owner. one thing i'm sure of though is (comparing my scope to other GX250s) that this isn't the original mirror cell, as it's completely different from the cell on the GX250 the guys at Opticstar in manchester have in their window. (different spider too).

just finished drilling and riveting the extra support and the hole in the centre of the cell is bang on centre of the tube now according to my digital vernier (give or take a mm)

[crashtestdummy]

Good skills

[Dave_D]

rough collimation with cheshire using a template i fix to the secondary with ellipses of the correct aspect ration (my secondary major axis is not correct for the minor axis to give 45 degrees with a cheshire for some bizarre reason) and my offset marked. you can just see where the laser hits the primary cell. time to clean up and put the primary mirror back in

[Dave_D]

finished... 

found a small amount of play in how the primary sits in the cell too... 3 sticky felt pads fixed to the ends of the three nylon adjuster screws fixed that so the primary is properly supported now and won't rock with changes in altitude.  

[SnakeyJ]

Nice work on the fettling Dave and sure this will perform very well at the end of the day.    It seems although OO has always been well respected for their optics, these earlier examples get a fair amount of stick for the build and focusers.    The newer VXs look very nice, but don't seem to change hands very much, which has to be a good sign that standards have radically improved!

[Dave_D]

Nice work on the fettling Dave and sure this will perform very well at the end of the day.    It seems although OO has always been well respected for their optics, these earlier examples get a fair amount of stick for the build and focusers.    The newer VXs look very nice, but don't seem to change hands very much, which has to be a good sign that standards have radically improved!

yeah, no issue with the optics, but they do need recoating. the focuser was the first thing i changed.

[leelee970]

I too changed the focuser - the original was not up to the job.

 

I also flocked the inside and did a complete revamp of the mirror cell which also included a cooling fan.

 

The next and final stage is to tackle the secondary spider - going to upgrade as the original doesn't hold collimation well.

 

So all in all there are only the mirrors that haven't been touched - and I have to say the optics are great.

Lee

[LeeB]

OO did have issues with build quality, my 10" took some sorting, new focuser, primary centering, cell rethread etc, optics are great however. the 12" produced alot later was far better with a great cell, even the focuser was ok but still swapped it for a 2 speed.  The tube rings on the 10 are also too thin the 12" are just right.

While it would be nice to be perfect from the get go, the most important bit the glass is superb in both scopes. I would much rather have it that way, than a lovelly piece of engineering with ploughed field optics.

The tubes are sometimes not perfectly round, its harder to make a thin wall aluminium tube perfect, steel is easier, but the weight saving makes up for it.

[Moonshane]

Personally, I'd only ever buy OOUK scopes out of choice, although this is generally used so I am not really a very good customer. I am paying more for a 50mm Ha scope than I paid for my 400mm f4 0.984 strehl mirror and tube/rings so personally, I feel a bit of tinkering is not a problem if the main components (i.e. optics) are sound. it's each to their own I suppose but used I feel they are great value for money.

all that said, other offerings are perfectly usable and give good images. if you don't want an OOUK scope then why not just buy another brand?