90-deg star-diagonal with a 'good' spotting/sight-scope question

[RT65CB-SWL]

Hi all,

On Friday, (27 Feb 2015), I attended my local societies 'Astro Basics/Beginners meeting'. I was asked by a disabled visitor/member what way around would the image would he/she see if they used a 90^o star diagonal in a 'good' spotting/sight-scope.

I apologise in advance if I appear rude, but the person is wheelchair bound, (unfortunately I cannot recall the make of the 'scope). They say it is appears to be an old anti-aircraft spotting/sight-scope and has used it with great success with some eyepieces so the image does appear the correct way up, but when they get to a certain angle in declination/zenith then they are stuck, and would a star-diagonal help?

[happy-kat]

Perhaps the current scope uses has a 45 degree angle where a diagonal would be, that would not be great to observe near zenith with very uncomfortable.

But a 90 degree one would be easier to observe zenith with.

It might be that they would use their existing arrangement for some viewing but switch diagonal for higher elevation objects.

You don't actually expand and say what'stuck' is.

I never get it right re view orientation so I won't reply.

[michael.h.f.wilkinson]

In principle it should work (you could also use a 90 deg Amici prism for correct image orientation). However, one must be aware that optical path differences might mean the scope will not come to focus.

[Peter Drew]

I think that getting a focus is likely to be the main obstacle. More details of the telescope would be helpful.