45 degree Dob view!

[Floater]

Pretty sure I'm going to feel stupid here (again!) but can anyone tell me what I'm doing wrong, please?

Have been using my frac mainly for a while now so decided to check out my Dob (as sig) and make sure collimation and finders were as should be. But the view through my eyepiece is not upside down, as it should be and has been in the past, but at a 45-degree angle! The attached image illustrates what I'm seeing.

Made a fool of myself before by trying to view through my frac from the side but can't figure what's up here. I'm steeling myself to feel foolish again ...

[John]

The normal view through a newtonian scope (which a dob is) is up and down and left and right reversed. The dob tube is rotated to put the eyepiece at an accessible angle so the image tilted too. It's perfectly normal and you are not doing anything wrong.

Refractors with a 90 degree diagonal show the image the right way up but left and right ist reversed.

It's something you will get used to.

It's a perfectly good question though so no need to feel foolish

[Floater]

Yes, John, thanks. But my view used to be up and down and reversed - not at an angle. And I can't think that I'm doing anything differently ...

[John]

Yes, John, thanks. But my view used to be up and down and reversed - not at an angle. And I can't think that I'm doing anything differently ...

You mean the angle of the view has changed since you last used the scope ?

[Moonshane]

I think of the view of a Newtonian as just upside down which inevitable leads to being left right reversed from the perspective of the 'eyeball view' but if you simply turn a map upside down it's correct.

[Floater]

Yes, John and Shane. The view used to be 'classic' Dob - vertical was upside down and horizontal was reversed. Perfectly happy with that all the times I used it.

Now the view is coming in at an angle of 45 degrees. Maybe my pic is not showing up properly but it's like this: \ - upside down but at an angle, coming in from top left to bottom right.

[John]

Assuming that we are talking about the same object viewed with the same eyepiece, for the orientation of the view to have changed since you last used the scope either the tube has been rotated or the optics have moved somehow.

[Floater]

In the vein of trying to give as much info as possible, the last time I used the Dob at night I used 2" EPs for the first time, swapping the 1.25" adapter and inserting the 2" adapter. This afternoon, while checking the finders, etc., I had gone back to the 1.25". I used the same view to fix the finders (a row of central heating pipes on a distant hospital roof) as I have always done. Before, they were always upside down and reversed horizontally. Today they were at the angle I have described.

When I made a fool of myself with the frac it was because I was viewing from the side, as with a Dob, instead of from behind the tube. And, boy, did I feel a tube when my error was pointed out! But I tried looking from various positions today and the view was always at this 45-degree angle ...

I'm baffled.

By the way, I also tried it with the 2" adapter today. Same problem.

[Charic]

Hi Gordon,........Going from your Frac to the Dob, is there any chance that an  image erector, eyepiece or diagonal has been transposed from one focuser to the next?

[jamespels]

This answer is from thinking about it and not from actually checking so apologies if it is utter rubbish - I will check tomorrow if possible. That said...

The newt OTA will invert and reflect the image as it "sees" it. Its natural position is with the focuser horizontal, at wich point images will seem upside down and back to front. Turn the OTA within the tube rings so that the focuser is no longer horizontal and "straight up" as the scope "sees" it is no longer straight up but at an angle to the horizon. My guess (yes, guess, until I check!!!) is that you have twiddled (technical term!) the OTA within the tube rings to aid access to the OTA or something like that. Either way, I suspect the focuser will be about 45 degrees off horizontal.

Note the huge caveat in the opening sentence but this is at least something you can easily check.

HTH,

James.

[Floater]

Hi guys. Thanks for your responses.

Chas, there is no chance of that at all. The scopes share only my eyepieces. In fact, the two 2" EPs I own have only ever been used in one session with the Dob and it has no diagonal or image erector, etc. as I wrote earlier, the only thing that I have done with the scope out of my normal practice is to use those 2" EPs. But that just involved changing adapters.

James, there are no tube rings involved. The OTA sits on the Dob 'turntable' and cannot be rotated or twiddled with. :-) I also thought that something must have 'twisted' and checked the secondary mirror - but all appears normal. I haven't poked around with anything and it's really bubbling my brain trying to figure it out!

But I'm sure I/we will! I have faith in the collective pool of wisdom. (Just terrified that it will be something very silly!)

[Charic]

jamespels........can a  150P Dob be rotated?

[Charic]

ok........I'm as baffled as you are then. 

"Just terrified that it will be something very silly!" ........if it is,  others can learn from mistakes, i wouldn't be overly worried.  And about the corrector,  I thought it would be doubtful,  but I I just can't think of anything else, but that won't stop me from looking.

[C7tsj]

Are you looking at a squint tree? Sorry Gordon, couldn't resist.

Mark

[jamespels]

jamespels........can a 150P Dob be rotated?

No idea!!! See comment re "guess"!!!!

Am curious, though - what angle does the focuser come out of the side at?

[Floater]

Mark, you're a rascal!

One thought here: I have fitted a so-called automatic focuser - an electric drive for the focuser drawtube. But I can't imagine that it would be possible to put the elements back in 'squint' ... Could it?

James the focuser comes out at 90 degrees, as per normal. And I'm viewing as I have always done.

Will try to get my head round the mod of the focuser and, failing any quick answer, will get into the innards of it. Pain and terror are just an arm's length away ...!

[Floater]

More I think about it, I'm putting my money on the electric drive thingie ...

[John]

More I think about it, I'm putting my money on the electric drive thingie ...

If its the only thing that has changed I guess it has to be a prime suspect. Quite how it would produce the results you are observing I can't work out though.

[Floater]

Me neither, John. All it involves is removing one of the focuser knobs and attaching the motor where the knob used to be, so to speak. Is there an element of the focuser which could turn or twist? I'm not aware of anything like that.

Furthermore, I'm pretty sure I've looked through the scope since fitting the drive and I noticed nothing wrong.

[Charic]

............like you say, just changing a focuser knob, shouldn't change the optical alignment  in any way?

[Floater]

Still discombobulated!

Removed the electric drive from the focuser and returned scope to 'as original'. And, unfortunately, as expected, no result. I have attached a couple of pics taken with my phone through the eyepiece. (Entierely by the way, but I am now even more amazed at what the imagers on this forum achieve, given my poor results.)

These are deadful, I know, but you'll get the idea I hope.

Pipes on a distant building which I normally use for aligning my finders:

And of a nearby weather vane:

I'm completely at a loss as to what I can try now. Just going over and over it in my head is driving me nuts. i can think of nothing that might explain what's going on.

For mercy's sake, if anyone has ANY idea please let me know ...?!

[Floater]

This is the scope, just to show the OTA cannot rotate:

and this is the focuser:

[Lorne]

Its all to do with your position when viewing, the view will always be the same but your eye will "perceive" it to be different. Try viewing standing towards the primary end of the Dob. keep viewing but move your feet round towards the front of the OTA, you will "see" the image moving - it isn't of course but your perception will think it is. ie, the treetop will appear to move from top right to bottom right. 

[Floater]

Thanks, Lorne, but I've tried every position, short of standing on my head.

The thing is I'm viewing in/from the same position that I always did - and it used to be a 'classic' Dob, uside down, view.

Thanks. nevertheless.

[Moonshane]

you need a night under the stars Gordon