Crossing the Flippin' Meridian?

[The Admiral]

Let me start out by saying that I've never used a GEM and so find it quite hard to visualize what contortions the mount makes to get the 'scope to track, or more precisely, exactly how the mount and tripod interfere with the 'scope's movements. Conventional wisdom says that when crossing the meridian the mount has to undergo a meridian flip. Now this is not a question about the pros and cons of doing this, there has been much written about that within these pages already; and I can see that when imaging towards the Northern skies either a flip is required, or else perhaps using a cranked pillar to support the mount head. But I would be confined essentially to imaging the Southern skies, and I was wondering if a simple pillar support for the mount head is sufficient to avoid the flip? I'd be using a 102mm f/7 refractor (with reducer).

Would it work, and what would be the issues?

Ian

[kirkster501]

No, a single concrete filled pipe as a pier may not be sufficient. It depends on the nature of your equipment. If it hangs to only two or three feet off the floor, the scope - especially a filter wheel or large camera - may strike the peer when past the meridian.  I have had this happen many times.  Some modern - and more expesnive - mounts can detect the change in torque and stop in the event of a pier strike. Many cannot.

Meridian flip is for a very solid reason.

[The Admiral]

Thanks Kirkster; I was rather more thinking of a pier extension to a tripod, the aim being to clear the camera of the tripod. I'm sure that what you are describing is self-evident when you see it in front of you, but for the life of me I can't visualize how that can happen , though I don't doubt what you say.

Ian

[Charic]

26 minutes ago, The Admiral said:

I've never used a GEM and so find it quite hard to visualize what contortions the mount makes................

That just took me back 4 Years?  the frustration of the thing, although I only suffered a few nights until the Dob arrived.

[kirkster501]

22 minutes ago, The Admiral said:

Thanks Kirkster; I was rather more thinking of a pier extension to a tripod, the aim being to clear the camera of the tripod. I'm sure that what you are describing is self-evident when you see it in front of you, but for the life of me I can't visualize how that can happen , though I don't doubt what you say.

Ian

Nothing to do with the height of the pier Ian.  Everything to do with the potential of your unique telescope and attached camera assembly to strike it after it tracks past the meridian and keeps going to the West.  This tends to happen most when the scope goes past the Meridian and is pointing high in the sky towards the zenith and you have a large filter wheel facing towards the pier.  The only way you'd avoid this is if the telescope and camera were short enough that the extended length of the optical system (i.e. scope and camera) was such that it did not extend past the RA access enough to strike the pier that supports it. This was the case with my very short FSQ85 an camera - there is no way it could strike the pier.  However, with a longer scope such as my TEC140 it will.  Even if the pier was 100m high, it would strike it - the height is irrelevant.  Your scope is still mounted atop that pier and if the scope is long enough it will strike the pier at some point west of the Meridian.

For these reasons, many scopes know when they are *past* the meridian (within seconds) and give you the option of setting how far past the meridian you need to go before you must do a flip so the scope does not strike the pier.