potentially daft question - image orientation 250px dob

[Jase_v2]

Apologies in advance  - but the image Im seeing when setting up in the daytime isnt upside down as I was expecting. Is this due to the position of the focuser , as its about the same orientation ( roughly 10 oclock) ? Or is my scope badly set up ? Must admit Im struggling with collimation, despite the excellent guides found on here!

[ronin]

The main mirror will flip the image both upside down and left to right.

The secondary will flip it left to right in a newtonian, thus cancelling out the main mirror in effect (it is not strictly a cancellation but 2 L-R inversions = no change).

So what you are left with is the top to bottom inversion so it comes out upside down.

Everything on a Newtonian is orientated around the angle that you have the scope angled at. So you get some "odd" inversion that is neither generally up/down or left/right unless the xcope is vertical or horizontal. Hence your 10 O'clock.

[Robny]

The main mirror will flip the image both upside down and left to right.

The secondary will flip it left to right in a newtonian, thus cancelling out the main mirror in effect (it is not strictly a cancellation but 2 L-R inversions = no change).

So what you are left with is the top to bottom inversion so it comes out upside down.

Everything on a Newtonian is orientated around the angle that you have the scope angled at. So you get some "odd" inversion that is neither generally up/down or left/right unless the xcope is vertical or horizontal. Hence your 10 O'clock.

I think the original post was asking why it is NOT upside down as expected  , that unfortunately I cannot answer.  What are you using to collimate, laser or Cheshire? And where are you finding difficulties?

[Jase_v2]

Yes, that was the original point of my (badly worded) question. Im aware that its flipped left to right and upside down  - but I was expecting an upside down image instead of the offset to 10 oclock . Ive tried a homemade collimation cap and a laser and cant get it blob on. Secondary mirror only so far, Im to unsure about altering the primary ! Thanks for the replies

[andyman]

Cant help with the initial question but mine does show a upside down image

[Reeny]

I get something similar when I use a magnifier lens.

I bought a second hand single element 2x Barlow which was rubbish.

Luckily, the lens unscrews from the bottom, so I use it as a 1.5x magnifier on my 9mm Plossl - to convert it to a 6mm equivalent.

When I use this arrangement, the image is swung around to 10 or 11o'clock for no apparent reason (about 45 degrees)

The image is pin sharp, so I just get on with it.

I don't know why it happens.

[NGC 1502]

A standard Newtonian gives an "upside down" view, or south up.    But that won't be exact, depends on the orientation of the focuser. The opening post mentions that the focuser is at "10 o'clock" so if you view a TV aerial or chimney it will be "on the slant" so to speak.  Nothing wrong with that, just normal.

When viewing the night sky, pan towards Polaris, new stars will enter the field of view on the north edge, pan east, new stars will enter the field on the east side.   That helps a lot with manual star hopping, and you read that an object is NE of another object or star.

If like me you regularly use a Newt (Dob) and a refractor with a star diagonal, the Newt is different from the refractor in that regard, but soon becomes second nature.

A collimation tip :- sort the secondary mirror first (centered under the focuser and pointing at the primary (ignore the reflection of the spider at this point).  Then center the reflection of the spider using the primary adjustment screws only, and the centre spot as a guide.  You can fine tune the primary on a defocused star at night.

Regards, Ed.

[Jase_v2]

M

[Jase_v2]

Ooops-hit the wrong key there.  Many thanks for the replies - I align my finder using pylons about 4 miles away. These appear to be running in from upper left top lower right  - ie 10 oclock down to 4 oclock and was expecting a vertical upsidedown image. Have just spent 2 hours fiddling with collimation using 'Astrobabys' guide. Hopefully is somewhere near now. Im taking my scope to our local club for equipment night, so will ask one of the more experienced members to have a look at it.

Not much chance of doing a star check tonight - hammering down here.