On Tuesday, May 23, 2017 at 5:42:40 AM UTC-5, Martin Brown wrote:
On 22/05/2017 08:07, wrote:
Hi,I've always used celestron stardiagnol,, recently I purchased a
celestron 90° erect image correcting prism,I've not yet used it.can
anyone tell me what differences to expect and the advantage and
disadvantage, if there is any,thanks.

Presumably on e of these as opposed to the more common simple Amici 45
degree prism.

https://en.wikipedia.org/wiki/Amici_roof_prism

Its claim to fame is that the image is the same way round as reality.

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Regards,
Martin Brown

What's reality? Everything is upside down inside your eyeball anyway, and your brain just makes the best of it. Scientists have outfitted people with special prism glasses that turns the world upside down, and after a few days wearing these glasses the people begin to adjust to the new reality and see the world as before, right side up.

Razzy