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