So these EQ mounts.. when i'm tracking an object (let's say, Jupiter) that's getting close to the meridian, the telescope is almost pointing straight up. Any further, and the bottom of the tube will start knocking the leg of the tripod.
So what's next?
Do I need to basically need to re-orient the scope so that the whole thing is facing west of the meridian? I guess i'll need to rotate the OTA as well to get the focuser in a useable position?
I usuallly try to avoid the meridian for this reason...I don't like the sound of a motor hitting its limit.
Actually one night I was setting up the scope and one of the alignment stars was very close to the meridian. By the time I finished the alignment I think it had gone to the other side and the scopes poor little brain couldn't handle it! It got stuck in a loop and I had to reset...so now I don't choose stars close to the meridian for this reason as well.
What they all said Mike, and yes it is one of those unfortunate things with a GEM. A bit of planning helps, as if the object is close to the meridian to start with, then you might as well, get the scope on the east side, so that it can pass through, and continue west unimpeeded. Depends of course on how tight the clearance is. With mine, and a wee small scope I can go a couple of hours at least either side. Yours, hitting the legs, sound different.
I doubt that with the webcam you would need to rotate the tube, just unplug the camera cable and resight the scope. The focuser will of course be on the other side, but again shouldn't be an issue.
Gary
For long exposure, auto guided astrophotography, another little trick is to keep the mount "heavy" on the East side, so that this very slight imbalance helps keep the gears meshed.
So, when the OTA is on the W and the Dec shaft/counter weights are on the E, you slide the weights slightly further down the shaft to make it slightly heavier on the E side.
After a meridian flip, the OTA is on the E and the Dec shaft/counter weights are on the W. You now have to slide the counter weights up the shaft so the OTA is slightly "heavier" which again should ensure the gears are in constant mesh and not in “free fall”.
As an aside, my Vixen GPDX and Skysensor 2000 warns me as I approach the Meridian, and will command a Meridian flip if you accept the warning notification. It also avoids cable wrap by going the long way around on GoTo slews as required.
MMm, the dark secret of the GEM - the Sphinx knows about this too, puts up a warning and offers to reverse direction for you or you can override (or ignore) then it lets you continue for about 30 mins past 12 but then it goes into a nodding pattern.
Sometimes the automatic reversal is not correct and the slew has to be stopped. If this happens I pick a target on the other side of the meridian and slew to that - adjust the balance, check alignment and the go back to tthe target I was on when it is clear of the 30 mins window. Of course the target is now the other way up in your fov - and if you were autoguiding you will need to reverse correction directions (or better re-calibrate).
And this, Meridian Flip, is the primary reason I love fork mounts. I can leave it running automated and not care about crossing the meridian other than scripting a re-focus.
I hate to think the horror of automating a meridian flip - making sure you're back on the same spot of sky and somehow getting the pointing accuracy to do that and retain a guide star.
When I do photography with my GM-8 I stick to one side of the meridian for the entire night, rather than complicate the whole process with a flip that will potentially mess up balance, image rotation, having to find a new guide star, etc etc.
Sorry, can't help other than to suggest buying a fork mount
I hate to think the horror of automating a meridian flip - making sure you're back on the same spot of sky and somehow getting the pointing accuracy to do that and retain a guide star.
You'd actually be surprised. With the integration of the right software tools you can plan your exposures to mitigiate a meridian flip causing issues. Tools such as CCD AutoPilot - http://www.ccdware.com/products/ccdap3/index.cfm and Observatory Control Software - http://acp4.dc3.com/index2.html
will actually finish the exposure, wait for the flip, re-focus, re-calibrate, find a guide star and re-commence imaging automatically. Very powerful. It does take some time to set up and I've had a few mishaps. It makes imaging aquisition much easier.
I agree it should be that easy, but I doubt it would be, not for me at least I use CCD Commander and it's capable of handling Meridian Flip like you suggest those others can, but I know it wouldn't go well for me. My narrow FOV makes pointing accuracy and suitable focus stars and guide stars tough at the best of times, let alone when you move the hole way across the sky, flip over and back to the same point
I personally find the use of a lowly paid astronomical apprentice solves my problems; they do all the meridian flipping and target re-acquisition, whilst I throw lavish soirees and keep the guests entertained.
I let them come indoors when it rains…..more than 100mm per hour that is……..
After a meridian flip, the OTA is on the E and the Dec shaft/counter weights are on the W. You now have to slide the counter weights up the shaft so the OTA is slightly "heavier" which again should ensure the gears are in constant mesh and not in “free fall”.
Dennis
And here is why - look what happened to my guiding when I did not rebalance after hitting the meridian - the mount keeps on tracking but...
