Orion Optics VX12 F4 pv1/10 Newtonian Scope

[jam1e1]

hi all

So 3 months in the making since order at Astrofest, scope has finally arrived! No chance for first light yet, brief summary below with comparison to SkyWatcher 250pds:

Packaging

Came well packaged in box similar sized to SW250, double boxed and plenty of bubble wrap / foam for protection - no issues here

Scope Size

As expected was similar to 250pds in length, only slightly longer, aperture 2" larger on OO. See comparison photo for sizes. Weight wise, the OO does feel slightly lighter although haven't put on scales as yet.

Scope Caps

See 'covers' photo where have placed the SW cap on top of OO so can get an idea of aperture difference. The OO cap is a soft plastic, whereas the SW is solid plastic. Only thought is hope it doesnt warp over time. OO include 2 caps, one for each end which is nice touch to keep out dust etc.

Focuser

The focuser does feel a lot more mechanically robust and smoother to turn than the SW one. (Feels similar to a starlight focuser). Looks well machined and certainly feels like an upgrade compared to SW. The compression rings are a good improvement so doesnt mark EPs. Height wise its slightly more lower profile too, also has been positioned to optimise for use with TV Paracorr. Good thing is the Focuser is similar height hence should have no issues with EP position.

Primary Mirror

Looks nice and shiny with center spot - without a clear sky cannot say much more  looking forward to first light. This is pv1/10 model, so if their marketing lives up to the hype, views should be sharper under good conditions! All appears collimated ok . Internally the scope walls appear rendered with similar black paint to SW, may flock it at later date though no rush to at the moment.

Secondary

The OO secondary is larger than the SW. One point to note as seen in the photos, the SW secondary is flush to the spider, whereas on OO mirror appears to be glued on - not sure if really makes any difference. The OO vanes are slightly thicker and overall the spider appears more robust. Whats nice is the screws for collimation vs allen key type nuts on SW - a lot more easier to collimate in my view. 

Rings

The rings are flatter but wider, also use bolts with heads that appear slightly easier to grip - should help in cold if need to use for any reason.

Rear

The scope includes a fan on the rear which should help cool quicker. Mirror cell holder looks robust. Collimation screws appear ok though smaller that SW ones - expected bigger ones, though hope no need to adjust for now. In my opinion would have been nicer to have larger ones just so can grip easier. May not be an issue at all, just initial impression.

Accessories

Included are an 8x50 finder and shoe, electrical connectors for fan, a black holder thing which i dont know what it is (8x30 finder holder?) also an optical report and welcome letter. Nice to have all those included, only note is it doesn't come with a dovetail, though given aperture size and some people to mount on dob base can understand why. 

Any issues / concerns

Only slight concern was when took bottom end cap off, found a chip of glass and also a couple of other smaller glass debris in the bottom - from inspecting the mirrors in situ (i.e. not un-screwing everything just what can see from line of sight) cannot see any chips on either mirrors. My guess (& hope) is it could have come from factory. My guess is as the mirror surfaces look fine then shouldn't affect views at all if does come from mirror. I'll give them a call tomorrow to ask about it.

Conclusion so far

Overall very pleased so far, does feel like a good upgrade from many aspects in comparison to SW, as above only minor comments are the small collimation screws on primary and glass debris in bottom. Given the similar weight and EP position, with extra 2" aperture but slightly faster F ratio, feels like a good compromise and upgrade - will update once get a first light chance

Jamie 

[DRT]

Great report, Jamie - now I know what to expect when mine arrives in August

Looking forward to your first light report.

[John]

Nice Jamie - I'll look forward to reading your 1st light report.

It's interesting looking at your scope compared to my SPX 12" F/5.3 which was the similar spec scope to the VX but around a decade back. Not a lot has changed !

I guess thats because it works

[t0nedude]

Nice scope, looking forward to first light..

Tony.

[Mark at Beaufort]

That is a fantastic scope which will be brilliant on DSOs. I am glad that Orion has improved on the secondary collimation screws. When I did the owners review on VX8 for the Sky at Night magazine last November I stated that the provided screws were not good and I changed them. I have also changed the Primary collimation screws because I felt the provided one were too small.

Not good to have glass chips that should have been checked before being despatched you - glad that it appears not to have caused problems to your mirror - however, they should be told.

Good luck with first night I am sure you will enjoy it.

 

[cs1cjc]

It is very nice!  My 350mm F/4.6 gives superb views,  for example a clean view of M57 at 350X on one night in the UK (no central star..).  It really goes deep for for galaxies, dozens on a number of nights, under what were somewhat polluted skies in the village in Derbyshire in which I lived.  For various reasons I have not yet used it here in Devon, but this should soon change, I hope.

I have had no issues with the optics and I have not flocked mine.  The cell support is according to Plop an optimal 9-point support (unlike the 3-point support I have on an earlier 200mm model).  From a theoretical point of view I would want a curved spider but I am not convinced about which configurations are both mechanically stable and do a good job of smearing the spikes out. 

I am also purely a visual observer and I do use an Altair Astro model which does a good  of cleaning up the coma inevitable in a Newtonian.  With a correctly collimated the scope I find the image is much more "refractor like" and no longer declines in brightness and contrast towards the edge, but I am very aware that most observers are happy without one.

The fan is a very important addition,  On many Derbyshire nights the mirror would not cool quickly enough to keep up with dropping air temperature with the inevitable result being tube currents which damage the view.  The fan configuration (small, push fan on mine) works well at clearing this.  However I have demonstrated, but only to my own satisfaction, other configurations which worked better in my tests.  Best I now believe is to seal the back and use a lower speed larger fan in a pull configuration.  I will write more about this later when I am less tired...

[niallk]

Congrats on the scope - she's a beaut, and those mirror specs are very impressive 

Hope those glass chips are benign - I think you are doing the right thing informing OO straight away.

[rl]

I revamped a very old 12" DX300 with a 1/10 wave mirror set (which was quite hard since the new mirror was twice as thick as the old one). I have always been very impressed with the result. Even at f/4 the planetery performance has been very good on the few nights that allow full exploitation of the aperture. I find a  12" at f/4 is a very compact and manageable light bucket that is very easy to take out and use quickly.  You should have years of fun with this one. Enjoy.

RL

[Paul73]

Very very nice. That is a tidy package.

That mirror should be fantastic. I've just moved from an SW 10" PV ??(1/4ish if we were being kind) to an OOUK 1/6 wave mirror and the difference is noticeable. So even allowing for the law of diminishing returns 1/10 should be awesome.

Enjoy.

Paul

[cs1cjc]

As ever my post was not free from typos.  On this occasion I left it too long so I can no longer alter it.

So when I referred to "an Altair Astro model", I was referring to this coma corrector: http://www.altairastro.com/altair-astro-photo-visual-coma-corrector-and-field-flattener-for-newtonian-reflectors.html.  At F/4 the diffraction limited field of a newtonian is tiny, 1.7mm in diameter, around 5 times the diameter of Jupiter and a fraction of the field of a high power eyepiece like 5mm Delite which gives a power of 200x in this scope and has a field stop of 5.3mm diameter.  It seems to me to it would be crime to spend good money on a fine mirror, so suitable for wide views, for it to perform at less than diffraction outside a 1.7mm circle... 

In passing the information of the diffraction limited field may well be different from that I have quoted in the past because different writers use slightly different formulae.  This information comes from a post by Sue and David French, both well renowned writers on Astronomy matters, at: http://www.science-bbs.com/17-astro-amateur/b644ab345abef4c0.htm.

[cs1cjc]

I promised to write more about my "Success with Fans" (the name of a long thread about the matter on Cloudy Nights). The management summary of my recommendations is as follows. 

 

Seal the back of the tube, leaving access to the collimation screws.  This is only to ensure that the bulk of air travels along the tube so it does not have to be very airtight.  I used corrogated cardboard, but better would be impermeable packing or other foam.  Invert the flow of the fan by turning it upside down (do not try to run it backwards by inverting the electrical connections, because it will not run and the motor will probably be destroyed). 

Now if there is:

a) no vibration visible at above the highest likely power you will use, 300x or 400x times perhaps and

on a star test (a real star is good and Polaris does not move!), no visible turbulence from air flow around the secondary and

c) again on a star test, there is no sign of tube currents distorting one side of a star test;

then you are good to go.  Run the fan while observing.  You will find your scope ready to use very quickly, producing clean images at a modest difference between the mirror and air temperatures.  I have not discussed these suggested changes with OO UK, having failed to engage with them on a couple of other matters.

 

For the tests and details of how to deal with any problems encountered in the about process, read on.  My tests were almost all performed on my 200mm and were hardly completed when I moved.  However, I see no reason why my findings would not be applicable to other sizes of telescope.  I am writing from memory, because I am still not quite sure where my day book is.  Even if I found it, such is the lack of quality of my record keeping, I could probably no longer interpret my notes.  So make of this what you will.  I would really value somebody replicating the work to see if their findings match mine, or not...

I used a star test on an artificial star, Hubble, to try to determine the cause of the lack of apparent performance of my 200mm newtonian.  At first I could not recognise the star test which showed clean rings on one side of the view and mush on the other.  I realised after a lot of thought  (sadly I am much slower in my 60's than when I was half that) that they were similar to the patterns from the invaluable text, Suiter, for tube currents but with the distorted ring area caused by tube currents in Suiter replaced by mush because the tube currents were turbulent. 

I used a hole cutter to make a 50mm hole in the closed tube bottom and fitted a fast 60mm fan to push air up the tube.  This was intended to be a permanent arrangement, because I expected it to resolve the matter, but as is so often the case, this engineering problem was more complex than hoped.

Having no success on Linux with a USB thermometer (now it looks as if it would play with Android), I used a dedicated digital thermometer with one probe attached to the mirror with blu tak and one taking air temperature and I recorded temperature every ten minutes or so in the time honoured manner, with pencil and paper.  I used an egg timer to ensure reading were not missed (often) and were (reasonably) on time.  The probes did not read the same in any algorithmic way so I had to use a correction table on one reading to match the other.

The fan cleared the turbulence, but it had only a marginal effect on the rate of cooling...  Now on clear night in Derbyshire you can start the evening at perhaps 15°C and finish well below freezing, a change of sometimes over 20°C!   Even with the mirror at ambient at the start it cannot keep up with the rate of change in air temperature so the limited effect on cooling was disappointing.  The fan would still need to be left on when viewing otherwise tube currents would restart in a few seconds unless the temperature difference is less than about 2°C.  The other possible issue, the impact on mirror figure of internal temperature differences, is minimal with low expansion glass as used by OO UK.

 

It was at this point that I talked with Jim Swithenbank, a long time colleague, friend and neighbour who knows everything worth knowing about fluid dynamics.  He was not happy about the fan pushing what was still turbulent air up the tube.  It would still damage the image, but would be hardly visible in an star test because the effect was now smeared over the whole area.  Instead he suggested that a pull fan would pull clean air down the tube.  It needs to be slow (have a low Reynolds number) so that the secondary mirror does not cause turbulence, but it needs to be strong enough to capture any warm air coming from the mirror.  I left with a number of books and was told to read up on fluid flow around a bluff object, in this case air around a mirror.   The fan would have to remain on during viewing, otherwise at, even a modest temperature difference of 2°C or so, the tube currents would restart in a few seconds.

I bought a lower speed fan which was free of visible vibration at even the highest power of 350x.  I fixed it with velcro so I could turn the fan over to turn both pull and push configurations.  I was easy to see on a star test that a pull configuration gave the cleaner image.  The was the last of my testing as we started to pack to move house.  The fan is still attached with velcro and the digital thermometer is still dangling inside the tube.

 

So I can now expand on the management summary above.  Seal the back of the tube, leaving access to the collimation screws.  This is only to ensure that the bulk of air travels along the tube so does not have to be very airtight.  I used corrogated cardboard, but better would be impermeable packing or other foam.  Invert the flow of the fan by turning it upside down (do not try to run it backwards by inverting the electrical connection, because it will not run and the motor will probably be destroyed).  Now if there is:

a) vibration visible at above the highest likely power you will use, 300x or 400x times perhaps, then you need a lower speed, and hopefully vibration free fan (or run the existing fan more slowly with lower voltage or a ballast resistor by trial and error).  Some are marketed as low vibration and this worked for me.  Repeat until no vibration is visible.

on a star test (a real star is good and Polaris does not move!), if there is visible turbulence from air flow round the secondary, then you need to reduce the speed of air down the tube.  You could reduce the power of the fan electrically, but it is simpler to put holes in the foam tube end seal that you have so carefully made.

c) again on a star test, if there are tube currents distorting one side of a star test, then you need a stronger fan, but it may be possible to make your existing fan work harder with a (modest!) increase in voltage.

Then you are good to go.  Run the fan while observing.  You will find your scope ready to use very quickly, producing clean images at a modest difference between the mirror and air temperatures.  I have not discussed these suggested changes with OO UK, having failed to engage with them on a couple of other matters.

 

I hope this is useful and I am sorry it became a saga.  Please forgive the inevitable typos...

[jam1e1]

Thanks for all the comments

Spoke to OO yesterday to inform them of the debris, as far as can tell it doesnt appear to have come from the scope, would need to take out mirror cell to 100% confirm but dont plan to at moment.

Thanks for fan advice - never used one before so will be interesting to see how this affects views.

Nearly got first light last night - unfortunately didn't realise (when skies cleared) SW dovetail doesnt fit on OO rings due to size mismatches (curvature and bolt size) - so close but so far!! have ordered dovetail which should arrive any day soon, should be ok to go from there  

[cs1cjc]

I will just take a step back from my earlier post, because I started at step 1 rather step 0. Not everybody has the temperature drop challenge of a clear Derbyshire night and if your scope is not broken do not fix it!

If your scope cools adequately in the normal way, then do nothing.  Your scope is cooled adequately if you see a clean round star test image, with the fan off.

If the star image is distorted on one side then you do have a problem and you may want to consider the advice in my post above.

 

[Paul73]

Cs1cjc

Thanks for the detailed postings. I'll be fitting fans at some stage and your postings will figure in the configuration decision.

Paul

[daveb]

On 17/05/2016 at 21:13, jam1e1 said:

Thanks for all the comments

Spoke to OO yesterday to inform them of the debris, as far as can tell it doesnt appear to have come from the scope, would need to take out mirror cell to 100% confirm but dont plan to at moment.

Thanks for fan advice - never used one before so will be interesting to see how this affects views.

Nearly got first light last night - unfortunately didn't realise (when skies cleared) SW dovetail doesnt fit on OO rings due to size mismatches (curvature and bolt size) - so close but so far!! have ordered dovetail which should arrive any day soon, should be ok to go from there  

I had to redrill and coutersink tube rings to get the dovetail to fit?

[Piero]

Nice one! It looks just great! Have a lot of fun with it! 

[jam1e1]

Finally had this out for a couple of sessions - from what seen so far am very impressed  

The best description to summerise would be tight, sharp and bright stars. Has a play with 24mm Meade, 17mm and 12mm naglers around cygnus, lacetera and Cassiopeia constellations.

Double cluster was fantastic, nice and bright with good colour depth on stars ranging from many bright whites to a couple of bronze. Doubles with different colours showed up really well (alberio i think in cygnus) - can really make out the different shades. Open clusters were really nice - the shades of reds , bronze, blues, whites and yellows really starts to show - spent ages just wandering aimlessly around these constellations. Deepest mag star could see was 13.7 (providing got the right one that matched up in skysafari app) - surprised given level of light pollution round here.

 Catseye really nice - blue shell really showed up and felt could almost make out the transparency of the shell. M13 was great sight, nice tight stars on edge and could make out slightly more of the core compared to previous scope. Clouds came in so didnt get too long.

Overall very pleased and looking forward to more sessions!

[DRT]

Glad to hear you are pleased, jam1e1.

I think you need to update your signature

 

[jam1e1]

On 8/25/2016 at 22:02, DRT said:

Glad to hear you are pleased, jam1e1.

I think you need to update your signature

 

good point just done - i turned signatures off hence didnt notice  

Bought a new laser collimator too to help ensure accurate collimation (hotech), seems to have done the trick!

[DRT]

I use a Hotech too.

I read a few bad remarks about lasers so bought a Cheshire and found that both the Hotech and Cheshire showed the same alignment