5D III V 5Ds ?

[TheRogue]

I'm assuming the 5Ds came out before the 5D III ?  What would be the reason to chose the more expensive 5Ds over the 3?

[RobertTheFat]

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@ebiggs1 wrote:

Tim when we built the 30" a Powell Observatory the biggest feat was keeping that huge mirror flat.  It has many adjustment points under it, I can tell you!

I know the new technology lends itself to multi-mirror set ups.  But back then it wasn't available to us amateurs.

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When you say "flat", you mean "parabolic", don't you?

[TCampbell]

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@RobertTheFat wrote:

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@ebiggs1 wrote:

Tim when we built the 30" a Powell Observatory the biggest feat was keeping that huge mirror flat.  It has many adjustment points under it, I can tell you!

I know the new technology lends itself to multi-mirror set ups.  But back then it wasn't available to us amateurs.

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When you say "flat", you mean "parabolic", don't you?

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I've never seen the 30" mirror Ernie mentioned.  But I assume he is referring to the back of the mirror (not the optical surface on the front).

The solid mirrors are actually fairly thick (and heavy).  The back is flat and the front has a curve (depending on the optical design it could be parabolic - but there are designs that use other curves).  The mirror requires supports behind it so that as the telescope points to various spots in the sky the mirror would tend to deform under it's own weight (if not properly supported.)

[ebiggs1]

"... the mirror would tend to deform under it's own weight (if not properly supported."

Exactly.

If this link is OK it is Powell Observatory.  If not google Powell Observatory.