45 degree Dob view!

[DRT]

Gordon,

Apologies if this is a stupid question but is your secondary mirror square on to the focus tube?

The reason I ask is that I bought a second-hand Newt a few weeks ago and when I checked the colimation I found that the mirror had been rotated about 5-10 degrees. I didn't check at the time but perhaps this would cause the image to be at a slightly different angle.

My head hurts thinking about  this, but probably not as much as yours does!

Derek

[Floater]

Derek, thanks. But yes, secondary is as it should be. Checked and double-checked because it seems as if the answer must lie in something to do with the reflection being tilted. Scope hasn't been bashed or ill-treated but have checked all mirrors. I even delberately put it way off collimation, in case it had something to do with the primary, and then brought it back again. It is collimated to the nth degree!

And yes, it is a head-hurter. I keep running through the optical train - EP, secondary, primary and then back through primary, secondary and EP. What can make it go off like this?! The focuser is rack and pinion, so can't twist.

A confustication indeed.

Shane, you're the Dob man and you will know that a night under the stars with a scope in this condition will be more than challenging!

[John]

....Shane, you're the Dob man and you will know that a night under the stars with a scope in this condition will be more than challenging!

On the other hand, the stars and other astro objects might look completely normal when you look at them.

I'd certainly give it a try before concluding that there is something major amiss. These scopes are not designed for looking at terrestrial objects after all although the weather vane photo looks more or less as I'd expect it to with a dob - upside down but tilted to one side.

[Moonshane]

I actually think James is correct in that the angle the focuser sticks out of the tube affects the view through the eyepiece. your scope has the focuser set at approx. 45 degrees if you look from the front end and down the tube. mine are generally a bit lower than this for my own convenience. my view is more like a up down reversal but yours is how I would expect it to be for a 45 degree setting.

think of observing at the zenith (in Dobson's Hole). here the objects are quite hard to get in the eyepiece as you don't move the scope up or down in certain positions but rotate it to go up/down or left/right. it is quite counter-intuitive but try it next time out. find a star at the zenith and try to get it in the eyepiece. I suspect you'll have to rotate.

think of the implications of this on your scope. if you could rotate it to get the tree to a more 'normal' position then I think it would work.

personally as 'there is no upside down (nor 45 degree angles) in space', I would just forget this and get on with observing. It will make no difference whatsoever and I suspect that nothing has changed other than your perception.

I hope this does not seem rude in any way, I just think you are mistaken. unfortunately I cannot test this as all my scopes are of too long a focal length to easily focus on the end of my garden! 

[Floater]

Thanks John and Shane - at least for the encouragement! The weather vane and pipes are a fair distance, by the way. :-)

I know there's no up and down in space, etc., it's just that it will take me even more mental agilty to try to shift the Dob in the right direction.

Apart from that, it's just busting me up trying to figure out what has changed. 'Cos something HAS changed ...

[Coastliner]

Floater,

For what it's worth, I have had a 200p Skywatcher Dob for about a week (the same as yours). I have checked the collimation (I have not adjusted anything) which was ok, and have taken a pic of an aerial with a vertical mounting post ( so that looking at it naked eye the post is vertical at 6 o'clock like the weathervane). Looking at it through the scope the post leaves the field of view at 11 o'clock, which is exactly as You describe. I can't work out how to post the pic I have taken through the eypiece. I don't think there is anything wrong with your setup. I think it has to do with the fact that the focuser is mounted at 13:00 (looking at the front), which is the "reverse" of 11 O'clock.

If you picked up the tube and rotated it so the focuser was on top, the leg would exit at 12:00. To get a correct up/down orientation you would have to rotate the tube so that the focuser was at the bottom.

Let me know if/how I can post the pic, I'll happily do so.

Neil.

[Moonshane]

why not try to put the scope upside down on the mount? this should change the position of the tree?

[knobby]

I reckon it was always like it ...

[Floater]

OK folks, I really, really do appreciate your responses and how you've taken the trouble.

Neil, I think you need to choose 'more response actions' then 'attachments'.

Shane, you're being a rascal. If I rotate the tube how can I get at the finders and eyepiece without crawling around under the setup? Even then it wouldn't be right.

Knobby, you're suggesting I don't know what I'm seeing.

Thing is that my first views through the Dob brought the usual response - 'it's upside down!'. My good lady said 'that's not much use, is it!?'. It was 12 o'clock to 6 o'clock. Now it's 10 o'clock to 4 o'clock. My good lady now says 'why has that changed!?'.

If the Mods allow it, I intend to take a different tack and offer incentive ...

[Coastliner]

For some reason uploading this pic alters its orientation, as described earlier the "stem" should point to 11:00. Nevertheless, the point is made that although the stem is vertical in real life the view through the eyepiece is orientated according to the position of the focuser. I still maintain that your scope is behaving normally.

Thanks for the upload tuition!

Neil.

[Macavity]

I looks to me like the focuser assembly is at approx. 45 degrees to the vertical.

Thus the image would also appear to be at approx. 45 degrees to the vertical?

If I look in a *plane* mirror, at vertical objects behind me, then lean over 45 deg,

keeping my eyes level, objects will appear rotated the other way by 45 deg, No? 

Just been out to look at my EQ mounted Newt in "resting" (horizontal) position... 

Due to orientation, the focusser is angled 45 deg below(!) vertical, looking into

the OTA directly. To set a distant object to the vertical (As I do for testing) the

video cam (chip) has to be rotated at 45 deg in the focusser. That in *practice*

and without any (far to hard for me!) "thought experiments"? 

[wheresthetorch?]

If you keep your head upright and look through the dob at three different objects: one at the horizon, one 45 degrees up and one at the zenith, the view of these three objects will be rotated through 90 degrees in relation to each other. The objects you are looking at to test the dob are probably about 30 degrees above the horizon, hence the orientation.

Mine's Isle of Jura please! :-)

[Floater]

Nice choice of whisky, wheresthetorch, but you're missing the point, I fear.

Same object, same angle - but now a different view through the EP. Ask my wife. Few people disagree with her (and get away easily).

[wheresthetorch?]

Ah, if it was the same object then my theory does indeed founder. Ah well...

[Lorne]

For some reason uploading this pic alters its orientation, as described earlier the "stem" should point to 11:00. Nevertheless, the point is made that although the stem is vertical in real life the view through the eyepiece is orientated according to the position of the focuser. I still maintain that your scope is behaving normally.

Thanks for the upload tuition!

Neil.image.jpg

Best pic of the ISS I've seen on this forum 

[Charic]

Gordon......looking at your  external pics of the telescope, it looks ok.   If you can't find a solution by end of week, suggest  we meet and set up Dobs, side-by-side and rectify this issue.   I'm only assuming where you live , but I`m about 40+ mins past Huntly!   If Huntly is midway for you, seems  a likely meeting point, providing you have transport to Huntly. Sunday  morning, would be the best  option  for me?.

[Coastliner]

Lorne - in daylight too!

[jamespels]

Floater, you told me the focuser sticks out horizontally but it does not - it is clearly at 45 degrees!

Will take some pics with mine tonight (sorry, didn't get a chance to over the weekend and explained this on completely the wrong thread but it involved damsels and jam ), rotating the OTA from horizontal through 45 degrees to vertical.

In short, though, this is exactly what would expect to see in your scope. Regarding its use, don't worry - my focuser ends up in all sorts of positions on its equatorial mount and your eye just seems to accommodate it.

[Coastliner]

Jamespels - Your thoughts are the same as mine. If we were to remove the OTA and lay it on a table pointing out of the window we would expect to see the orientation of any vertical rotate with the rotation of the tube, so that if we have the focuser on the top we would expect to see the verical inverted, but vertical, and the orientation would alter as we rotate the tube, the angle corresponding to the angle of the focuser.  Floater, I don't know what was wrong with yours before, but it's ok now!

[jamespels]

Floater, I don't know what was wrong with yours before, but it's ok now!

Ha ha ha!!!

[Tiny Small]

Are you on a hill you that didn't have before?

[DRT]

Perhaps some Visual Perception Correcting Fluid would help?

[Floater]

OK folks, they're selling tickets for the hanging ...

Public humiliation is not pleasant but it appears that is what I must accept! I humbly thank all who have responded (even the cheeky ones!) -and especially Charic, who went the extra mile via PM - and do hereby promise to admit that I am a daft old duffer when prompted.

I must accept, hard though it is, that I have misplaced my mind and convinced myself I've seen something which I have not.

If apologies are in order, then please accept them - in triplicate. I was not being mischievous or capricious; just glaikit! Even if you have never seen that word before, I'm sure you can work out that it doesn't mean clever ...

Over and out.

p.s. At least I know my scope's working as it should.

[Coastliner]

From one of the "cheeky ones", no apology required - this has been very entertaining, and I must admit that I started to doubt myself and did actually remove my scope from the mount and rotate it on a table etc. to convince myself!

As a relative newbie I've learnt from this thread, as no doubt you have!

[Moonshane]

I think this is one of those areas where it's hard to get your head around what's going on. my suggestion of putting the scope on upside down was actually genuine as it happens as you would have seen the effect of the orientation of the scope/focuser in action (even though you'd have had damp knees no doubt).

Just enjoy the scope and there's never any shame in questioning something that seems questionable in what is, after all, a science based hobby.