Which way up is my Sun?

[Tiny]

With the PST things on the sun went from right to left and up was down.

But today for the first time the clouds cleared and I had a PST out and also new filter on a normal scope.

There were six small flares (2 were loops) and maybe a hedge so there was enough to compare.

No surprise that the scope with the filter - which cost a lot - is much better than the (very good) PST.

However, the one thing we realised very quickly is that the two scopes both showed the same flares on the same side but what is top in the PST is bottom in the other scope.

I have always assumed the PST image is south at top. And, as far as I know the (televue) prism in the other refracting scope is not an erecting one but surely it can't be the filter doing it.

Any ideas.

[AstroTiger]

Its strange i was trying to observe some prominences yesterday, not loops mind you just tiny flare type things.

Now my produre is i use an eyepiece to see whats there first, then whack in the webcam and navigate to it after.

BUT its a good question, does the PST invert the image?

I have no idea!

[haitch]

Can't you tell which way is up by moving the scope whilst looking through it?

[Merlin66]

It's sometimes a difficult question to answer!

Depends on the scope, with/ without diagonal; on an equatorial mount or Alt-Az etc.

The best and most accurate method is:

Let the image of the Sun drift across the field; it will drift TOWARDS the West.

Moving the scope North (or South) will quickly indicated these directions.

[The Warthog]

The PST is a refractor, therefore without a diagonal, the image is inverted N-S and E-W. Wit a diagonal, it is correct N-S, but inverted E-W.

[Merlin66]

Caution!

The PST doesn't have a diagonal, but it does use a pentaprism to reduce the back-focus. This has three internal reflections... so will act like a diagonal....

[The Warthog]

OH.

[Merlin66]

Tiny,

You got my brain cells working!

I regularly use a DSLR for imaging and just realised ( Doh!) that unlike the old film camera's the image produced is not a negative ( like the old film!) but a direct view positive. This means that it must "correct" for the optics of the lenses and or scope...

OK, here we go......

I took a "target" North at the Top, South at the Bottom, East at the Left and West at the Right; just like you would see the Sun at Noon with the naked eye.....

1. Refractor with eyepiece only:

Image Inverted, and Mirrored ie

South at Top, West to the left

2. Refractor with diagonal and eyepiece:

Image Right way up, but mirrored ie

North at Top, West to left

3. DSLR camera image, with std Camera Lens

Image Right way up, East to Left

As per naked eye ( as you'd expect!)

4. DSLR camera, lens removed and body fitted to refractor:

Image Right way up, but mirrored ie

North to the top, West to the left

5 DSLR camera, lens removed and body fitted to refractor diagonal:

Image inverted, East to left

South at Top, East to left.

Sooooo, the guys who do the imaging with DSLR's get a DIFFERENT view from the visual guys!!!

Visual in the PST, I think due to the pentaprism, would be similar to #2 above.

[Tiny]

A moment of hazy sun so dived out with SS PST and found...

Move scope up - sun in scope goes up

Move scope down - sun goes down

Move scope left - sun goes left

Move scope right - sun goes right.

I make that South top, east right (I think) as all in view is reversed.

[Merlin66]

Tiny,

I really depends on the mounting you have the PST on and when you are observing.

With an Alt-Az mount the only time the North/ South is vertical is when you are observing an object on the Meridian. ( Sun at Noon)

As mentioned the best and easiest way is to position the Sun in the eyepiece, with no drive, and watch which way it drifts; where it leaves the field of view is WEST.

If, on the meridian, you move the scope upwards, ie towards the North and the Sun dissappears down the bottom of the field, then UP is North. So, based on your findings: if you were observing near Noon; then you're correct.

[tom.yates]

Think south is top unless the plane that flew through the field was flying upside down

[Merlin66]

In my SM60/ED80/DMK21 I get South to the top and East to the left.

So you are correct the plane was not upside down!!