Orion Optics VX12 first light

[Trentend]

After what seemed like an eternity (in reality just a couple of months!) a new dobsonian mount finally arrived from Orion Optics for my VX12. Took just a few minutes to build and a pretty accurate fit (not NASA standards and might need a little fettling in places but fine). This coincided nicely with a fullish moon and clear night so decided to set the scope up in the back garden next to my (soon to go) skywatcher explorer 200p for some side by side comparisons. Used my denkmeier binoviewer, powerswitch, ocs45 and panoptic 24mm in both.

What I liked: The VX12 was so easy to set up. Just 30 seconds carrying the mount outside first (very easy to lift unlike the eq5 mount and weights) and the scope fitted very nicely on to this with no fuss. It really is a great design, very small footprint and will take seconds to transport and set up at local dark sights which was the main reason for the purchase. I also liked being seated at the scope (new to me!) and the scope movement in the mount was very smooth.

 

What I didn’t like:  Views of the moon in lowest power were good, but there was a lot of atmospheric wobble right out the box. Didn’t get any of this at low, medium or high power in the skywatcher. Guess that’s the difference in aperture and I’ll have to get more patient allowing for cool down? Views at medium and high power weren’t crisp at all. Despite collimating beforehand, using a Hotech laser (red dot seemed to be in the right places) there was some blurring and I found myself switching back to the skywatcher for better views. I guess it’s back to the drawing board with collimation.

Could do better but not a bad start...

 

[John]

Good start !

I find my OO 12" F/5.3 dob is OK for low power straight out of the house but needs 30-40 minutes to cool down before higher powers are worthwhile.

If the seeing is wobbly then the larger aperture tends to emphasise that more than smaller scopes I think.

They are very easy to set up and use though - about as easy as a 12 inch scope can be I reckon.

[Starflyer]

Are you using the fan on the primary cell?  I find star shapes are pretty awful without running the fan for a few minutes, even when the scope's been cooling for a good while. 

I plug the fan in and the stars change from horrible blotches to nice round stars within minutes. 

[John]

53 minutes ago, Starflyer said:

Are you using the fan on the primary cell?  I find star shapes are pretty awful without running the fan for a few minutes, even when the scope's been cooling for a good while. 

I plug the fan in and the stars change from horrible blotches to nice round stars within minutes. 

Interesting. I don't find that I need to use the fan at all with my 12 inch F/5.3 OO

[Trentend]

I let the scope cool down for 3 hours last night, so hopefully that’s one less parameter out the equation. The full moon was pretty crisp and bright with the power switch on low magnification and 24mm in the binoviewer. The middle and high power though were very average and much better in the 8 inch skywatcher side by side, which I kept going back to. Appreciate the higher aperture increases the magnification (and presumably weakens the clarity like using a higher power ep?), but I just couldn’t get an especially clear/focused view. Not sure if this is collimation (likely) or sensitivity to atmospherics in a larger scope? There was noticeable wobble in the 12 and nothing in the 8.

I will give the fan a try.  What battery would people recommend for the cable connector I have in the picture below?

 

[Timebandit]

 

Some interesting first thoughts.

Do make sure the mirror is cool, and is at ambient temperature. This will cause problematic viewing otherwise. Keeping the scope in  a shed/obs is the best way to do this , if possible. The larger the mirror then the longer it takes to reach ambient temperature.

Do make sure the scope is properly collimated . As this will also have a effect on the quality of views achieved. Worth checking and double checking. My VX does seem to hold collimation very well once set up correctly.

Atmospheric conditions do come into play a lot ,and it is surprising how much one nights viewing can change, solely down to atmosphere. I know from experience using the same kit set up on different nights can have dramatic quality of views differences, directly due to atmosphere.

Like John I never use my fan with the 14vx , but it does live outside, certainly helps on cool down / ambient me thinks. I know some people do use the fan as suppose helps with tube currents.

 

 

 

 

 

[John]

My scope lives in the dining room but cools quite quickly without the fan being used. Once cool I find that 200x-300x gives really sharp, bright and contrasty views of the moon. I don't use a binoviewer though - just a single eyepiece (good quality one though !).

Collimation is quite important of course as Timebandit says, especially if your scope is one of the F/4's. My F/5.3 is a little more forgiving but I still keep in in good collimation and check this each time I use the scope.

Having owned the 8 and 10 inch Skywatcher dobs (and a Meade 12 inch Lightbridge too) I can say that the OO 12 inch should be fully their equal optically and probably a little better on nights of good seeing conditions.

 

[Trikeflyer]

You’ve probably checked this already but if the laser isn’t well collimated this can throw out the collimation of the scope, I speak from personal experience so I mention it just in case it’s factor for you. 

Hope you get it sorted.

Steve 

[jam1e1]

suggest check the collimation holds when move scope from horizontal to vertical and back to horizontal i.e 180 degrees using laser or cheshire and check dot doesnt move over course of the rotation- say this as my vx12 came with primary incorrectly fitted so had very slight play and lost collimation when moved. Managed to fix myself by taking mirror out cell and putting it back correctly adjusted, though took advice from OO to do it correctly to avoid over tightening and mirror pinching 

As per your points on cooling and multiple nights, definitely suggest give a couple more nights to get fair view as Ive had similar nights where seeing is poor one night and crystal sharp next....convinced myself scope was at fault when no more than basic atmospherics. As per johns point even though mine comes out 'cold' from garage still needs a good 45m to acclimatise for better views

[Trentend]

Hmm, interesting point jam1e1. I recall before I received the mount a month ago and had a go collimating with the scope horizontal, I sensed a faint amount of movement in the primary when slowly rolling the tube but had forgotten about that. Pretty sure this wasn’t the mirror itself rotating, but the cell. I’ll have another look tomorrow. If there is movement, is it an easy job removing the primary and a fix? Apart from not touching the mirror, any advice while doing this? There’s plenty of dust on the mirror but I’m not sure I want to tackle that.

[Rob]

Great points being made here. Basic rule of thumb that I go with is: scope out early (sunset). allow 1 to 2 hours to cool. Then colimate. A further hour/two collimate check & adjust usually only a Primary mirror adjustment here.

The mirror flop / movement is a very real thing. I found my OO SPX required more collimation inspection than my current 200PDS. Im sure the scope is ok. OO make amazing mirrors, its more likely to be an experience / seeing / collimation thing going on.

Good Luck! .. Rob

[Piero]

Mm...

I assume that you used the same collimation tool for both the telescopes. If your 8" is collimated fine (and it seems so as you got nice views at high power), I assume that you collimated the 12" correctly.

 

I have a few questions.

Cooling time will be longer for the 12". How much time did you leave the telescope out before observing?

Have you tightened your collimation bolts too much (pinched optics)?

Can you describe a bit better how the stars were blurred? Importantly, were they dots at the centre and blurred off axis or were they blurred all over the field? Did they appear like crosses? Or like comets?

Is your telescope f4 or f5.3?

Is there a way for you to know whether your primary mirror is glued to the mirror cell? 

Would it be possible for you to post the specs of your mirror? It's a sheet with the details about your primary mirror figure, PV, etc.

 

If I were you I would leave the telescope out for a couple of hours before observing. Then I would point the telescope towards an area where there are many stars (e.g. now around Gemini's feet, M35). So, I would collimate it and observe that area with a quality high power eyepiece without moving the telescope to avoid any potential mirror shift. Take a look at the stars and how they look, in particular if you cannot focus them. Then I would observe at lower and higher targets. Again, I would take a note about the appearance of stars.

[Stu]

@Trentend what does a star test look like? That's the best way to see what is going on with collimation and also cooling.

I think sometimes also you can get a stubborn boundary layer of warm air above the mirror even after it has cooled which is where a quick run of the fans might help. I would tend not to run them whilst observing; I recall being traumatised looking through my Sumarian for the first time and seeing stars which were lines instead of points. Switching off the fan fixed this instantly!

[John]

My OO 12 inch F/5.3 is an SPX with the simpler 3-prong mirror cell. It holds collimation really well even after I've transported the scope, tube on it's side, in a car for 15 miles or more down country roads. Just a tweak is usually needed.

One tip I've found useful is not to use the OO mirror cell locking screws after getting the collimation right, unless you are travelling with the scope. The locking screws can actually put the collimation out through the pressure they exert on the mirror holder.

 

[Geoff Barnes]

4 minutes ago, John said:

One tip I've found useful is not to use the OO mirror cell locking screws after getting the collimation right, unless you are travelling with the scope. The locking screws can actually put the collimation out through the pressure they exert on the mirror holder.

Yes, this is what I've found with my SW 12 inch Dobsonian, after collimating via a star test I leave the locking screws loose and the scope stays collimated for the rest of the session. Transportation would be the only time I would consider locking them tight.

[jam1e1]

On 21/04/2019 at 00:10, Trentend said:

Hmm, interesting point jam1e1. I recall before I received the mount a month ago and had a go collimating with the scope horizontal, I sensed a faint amount of movement in the primary when slowly rolling the tube but had forgotten about that. Pretty sure this wasn’t the mirror itself rotating, but the cell. I’ll have another look tomorrow. If there is movement, is it an easy job removing the primary and a fix? Apart from not touching the mirror, any advice while doing this? There’s plenty of dust on the mirror but I’m not sure I want to tackle that.

Suggest check it is definitely a primary related issue as per other posters comments before attempting any maintenance. In my instance I heard a definite minor 'clunk' sound, to investigate i put the scope vertical with primary on bottom, unscrewed the cell from the tube then gently lifted tube off. From what I recall, believe it was a slightly loose mirror clip that meant very slight play in the cell/mirror giving rise to clunk sound. I tightened this then readjusted the mirror cell screws as they were right at end of thread for some reason (way they came). Note I didn't need to take the mirror out of cell directly, moreover adjusted (apologies my post made it read like took completely out!). Either way once put back collimation held and clunk sound didnt return.

Going to try not tightening the locking screws - good tip!

[Saganite]

On 21/04/2019 at 11:15, John said:

My OO 12 inch F/5.3 is an SPX with the simpler 3-prong mirror cell. It holds collimation really well even after I've transported the scope, tube on it's side, in a car for 15 miles or more down country roads. Just a tweak is usually needed.

One tip I've found useful is not to use the OO mirror cell locking screws after getting the collimation right, unless you are travelling with the scope. The locking screws can actually put the collimation out through the pressure they exert on the mirror holder.

 

I have the same scope, and follow that advice. The collimation rarely alters during a session, even when trundled around the garden, and when / if it does, it is the work of seconds to readjust it.

[Trentend]

Appreciate all the feedback. Next steps are a) buy a battery for the fan (any recommendations given the cables in the picture above?), b) learn about the “star test” c) remember not to tighten the locking screws and d) gently roll the scope whilst in a horizontal position to see if there is something loose

Regarding the 8inch skywatcher, I’ve never collimation this properly (other than with a cheap laser) but it’s always shown crystal clear views at medium and high power in the binoviewer and panoptics.

 

 

 

[Trentend]

Any advice on the battery? Will only be using for the fan. Prefer something lightweight that will last around 4 hours in any 1 viewing.