What is the Ideal Pier Height for a Pulsar 2.7m Dome

[DeepSkyMan]

Hi there everyone.  I trying to decide on a Pier for my 2.7m dome.  Curious about what the ideal height is for the pier.  Height between the concrete and the lower point of the dome aperture window is about 1.8m.  The dome will house an ASA DDM85 Mount.

Kind Regards

Paul.

[fifeskies]

Would help to know what you plan to put onto the mount.

Ideal height for a 150 mm f10 refractor will not be the same as ideal height for a 300mm f4 Newtonian.

You may need to think about all the scopes you have and work out what will work for all of them.

 

Another factor would be the horizon you have from the dome, if you have trees/buildings restricting your view to over 15 degrees altitude this will affect the decision.

 

Also remember to offset the pier so the dome centre is actually the mount axis crossover in Dec and RA  , this is typically 100mm or so pier offset South for the majority of mounts in Northern hemisphere at Scottish Latitudes.

[ollypenrice]

I think the three key numbers are 1) the height of the space swept by the highest part of the scope in all positions. At no point should it be able to contact the dome because, if it can, it one day will. Maybe allow for the possibility of a longer OTA in case you ever change, and don't forget the dew shield.  This number is more likely to be an issue with roll-offs than domes but bear it in mind. 2) access to the lowest objects you are ever likely to want to image or observe. This number may be horizon-limited anyway, depending on your site. The scope needs to be able to see over the bottom of the slit.  3) neither end of the scope should be able to hit the floor. You might say to yourself, 'This only applies to the back of the scope' but that would assume that nothing will ever go wrong - and it will!  I host a number of robotic scopes and fairly regularly find them in positions of cable-tugging contortion...

All these numbers are specific to individual setups. Mount heights vary, as do scope lengths and horizons. This probably won't apply to you with the DDM but anyone wanting to track well past the meridian, as I do, will need to raise the pier because the OTA gets progressively lower after the meridian. This applies even more strongly with dual or side-by-side rigs.

I suppose the failsafe rule would be 'as high as possible,' consistent with not hitting the roof.

Olly

[Rusted]

I addition to the excellent advice so far.. imagine the scope [or dewshield] sweeping the inside of the dome.
Ideally the top should be concentric. If the pier is too high the dewshield may hit the top of the dome or any inward projections.
I had that problem with my 7" f/12 in my 10'/3m dome. Had to remove the huge dewshield.
Saddle offset, relative to the polar axis can soon find the limits of your dome with a long refractor.
The dewshield sweeps circles to the east and west of center.

I like to be able to see the distant horizon [woods] with my refractors. Just to be able to test resolution.
If you can't get that low then you will always wish you could.