I've been testing flexure this new moon cycle. This is the latest configuration of the scope.
What's changed recently:
- I've moved the rings on the main scope out to near the ends of the dovetail plate. This seems to give some stability to the overall system.
- I've removed the ring around the focuser on the SV70ED guide scope and replaced it with the foot that it uses. Hopes are that this will provide a firm base rather than a floating tube.
- I've added a direct support for the DSLR camera via the tripod socket. This has helped remove any movement that the camera has. Now the remaining flexure is just from tube movement rather than from focuser sag.
- I've also added another layer of aluminum strip metal under the main rings to shim them up and remove the gap that was left over after I removed the felt. It's an ugly job but it works.
- I still have the metal straps in place. I also have added an additional finder on the scope but it's just floating rather than providing support.
Here are the results from this work.
I noticed that there was still drift while imaging. So I turned PEC off to see if it made a difference. The RMS value didn't change, so PEC was not adding anything at the time. Easier to run with it off.
I think it's interesting that last night and the night before (11 & 12) both are exhibiting flex in X & Y, whereas before it was just in Y (RA). Not sure what is going on there. Maybe it's the insulation that I put under the tripod screw. I'll remove that and see if it makes a difference. Most of the X drift is between .25 and .6 pixel. Still significant enough to blur the stars.
What's left to try?
- Tripod screw tightening.
This is one of the main things I've changed recently so it may be the factor.
Update: This screw was loose. I've tightened it.
- Tweak east bias balance.
Since the drift curve is sensitive to the position of the mount at zenith, it makes me wonder if the position of the counterweight shaft makes an impact.
Update: I'm going to try using the hanging weight on a string to keep consistent pressure on the RA.
- Since I've added and moved bits along the axis of the setup, I'm going to make sure that DEC is balanced "camera heavy."
- Secure the shake reduction movement of the CCD.
I don't know if this moves when the camera is on or not or even what the tolerances are. The fact that the X & Y are acting up makes me think this is unlikely.
- Tightening up the guiding tolerances on Maxim/Increasing guide cam resolution:
Currently the guide cam is 2.55 arcsec/pixel vs the imaging scale is 1.9 arcsec/pixel. Usually I get RMS values of .3 pixel which is well under visibility on the main camera.
- Drastic changes would be to go with a side-by-side setup.