Calculating my pier height?

[Ivor]

I'm in the process of building my observatory, I will be putting up a thread after the weekend where I should have progressed a little further. I'm putting in the pier this weekend and I'm trying to calculate the height of the pier, referencing here http://www.bisque.com/help/paramountme/computing_pier_height.htmI understand this should be should be

Pier Height = Observatory Wall Height - OTA Centre Height (when point due south)

My challenge is twofold, firstly I'm planning to get some pier plates from AstroTec designed to support my current EQ6Pro and I need to add the height between the pier plates into the equation. Added to this I'm looking for the pier plates to made to support my current set-up and my planned future state which will be a MESU 200, unfortunately Graham appears to be on holiday so I can't agree the details.

As it is dry at the weekend and I have some extra manual labour available I need to crack on with the concreting before the frosts start so I need to work this out now. I believe the best way to approach to this is to find out the maximum combinations OTA height and add an approximation for the Pier plates.

So the new equation is:

Pier Height = Observatory Wall Height - (OTA Centre Height + Pier plate height)

Looking at pictures of the MESU 200 it unsurprisingly looks bigger than the EQ6Pro so I will work on the basis this is the maximum. What I need to know is the combined height of the MESU 200 fixings under the top plate plus the OTA height I can then use long M12 bolts to adjust for the difference between this and the EQ6Pro.

So firstly can anyone is a flaw in my logic?
Have I forgotten to take anything into consideration?
Can anyone tell me the OTA height for a MESU 200 plus fixings?

Thoughts?

[The Thing]

Hi Ivor,

When I build mine next year some time I plan to make it extra tall to try to make sure the OTA is above the moist cold frost prone layer close to the ground so it may be around 1.75m tall. For me this isn't a problem 'Real' observatories are always built up several meters for this reason. In Mark's observatory this is probably how high the OTAs are above the ground in front of the shed though I don't think it was a design consideration.

I have started on this book http://www.gbv.de/dms/bs/toc/185766625.pdf to see if I'm right to consider this.

[Ivor]

I see your point, circumstance means my wall height is 1.75m with a roof height of 0.75m so hopefully I'll avoid most of the moisture issues. The challenge is working out how much lower to make the pier relative to the wall, I'm very unlikely to image near the horizon due to the light pollution from Tunbridge Wells so I have some leeway.

[The Thing]

I should have mentioned that where my pier will be is only 7m ASL and 1500m from the coast with a stream at the bottom of the garden. So the area is prone to a low misty layer on moist nights in the winter.

[Ivor]

Either you are anticipating significant global warming and everyone outside the M25 should start worrying or more hopefully you have a remote site in mind

[The Thing]

Manche, Basse Normandie, France. And it's me that'll be remote from the M25!

[MarkS]

That equation means a large part of the telescope will always be above the height of the wall.  For a roll-off roof design like mine it would mean part of the roof would crash into the scope.   So my pier height was calculated to ensure the whole scope is below the level of the sliding roof parts and then I have a section of wall that folds down to enable the scope to see right down to the southern horizon without obstruction.

For a dome observatory then that equation will work.

Mark