On Tue, Jun 4, 2024 at 06:06 AM, BBasiaga wrote:
I'm set up on a permanent pier, which has 4'of concrete in the ground, and 8 embedded bolts per the 'pier bible' how-to book.? It's an 8" pipe on top of that and the MA Adapter is bored down directly with no 'rat cage'.??
I can get great PA and see guiding that shows minor oscillations in Dec both ways.? Then the next session I'll see good guiding but Dec is always correcting the same direction, and if I re-run PA it confirms I am off by a fee arc-min.? Easy enough to adjust, but with a permanent pier like this I would have expected less.??
I'm wondering if I have forgotten which direction the last move should be, and perhaps I'm seeing some settling of the gear after making adjistments.? So if I'm in front of the scope looking South, which way should my final move be- clockwise or counter clockwise??
Hi Brian,
My G11 is on a permanent pier so perhaps I can give a few tips. As Paul mentioned you should not be seeing much change night to night as the pier is not moving. I may see a few millimeters of change from summer to winter depending on how much moisture is in the soil and freeze/thaw moving it sideways ever so slightly. My concrete base is 4 feet deep into all clay, which probably yields a bit more than going into a rocky base.
But for the altitude and azimuth adjustment bolts, I switched to the Losmandy replacement knobs and also used some different washers underneath. I have two thin 3/8" ID washers sandwiched around a Belleville washer. So, by the time the Belleville gets flattened out the tension is about right. One washer under the knob or bolt can start turning a bit while tightening and start changing the resting position. Each final snug side to side on the knobs needs to be rechecked for PA changes. But even with the knobs tight you should still be able move the ALT/AZ adjustment knobs a bit for a final tweak if needed. When using the Altitude knob, I try to make the last tweak push the mount upwards to keep pressure on the inner gimbal. If there is no pressure or your last adjustment is downward, the ALT can sink gradually over time with the weight of everything pushing downward. If ALT changes your PA will not be correct anymore.
Not sure how you are measuring PA, but after I use the Pole Master inserted into the polar scope threads, I do a final polar alignment use the drift method in PHD2. Your main scope and guide scope need to be well centered with each other, so the drifting with the guide scope matches the cone error of the main scope. If using an OAG, you can select a smaller subframe in PHD2 and still use the drift method. Select Polar Drift Align under Tools and follow the instructions. You will need to adjust AZ with the scope pointed south and ALT with the scope pointed east. The Slew button in the Drift tool should move the scope the equator/meridian position. You will need to find a spot low in the east at the meridian using Stellarium or whatever planetarium app you use.
With all the dovetails and ALT/AZ locked down, my PA will stay put for months at a time. The only time it will change much is if I change scopes or bump into the gear in the dark.
Good luck,
John
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Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, Sequence Generator Pro and PixInsight user
Paul Kanevsky