In the past i’ve noticed a few posts in regards to improving pointing accuracy, and i think i recall seeing several references to “Offsets”. Can somenone please explain what these offeset’s are used for and how to configure them.
I normally use plate solving / SGP centering routine, but sometimes, the initial slew is way off (i.e. a few thousand pixels out and the auto centering funciton fails, and sometimes it just works flawlessly with the initial slew being within 50-100 pixels.
Just wanting to see if can find a way to get more consistent pointing, by building up a model.
First, what mount are you using?
Second, sometimes a pointing model can actually get in the way. If you are
using plate solving to center your target there isn’t any need for a
pointing model. I never bothered to set up a pointing model on my old G11
or my current Mach1GTO.
Finally, I’m not sure what you mean by “offsets” relating to plate
solving. The only “offsets” I’m aware of in SGP is related to
autofocusing. Ex. If I auto focus with LUM and use an offset focuser
position when changing to another filter after the auto focus.
I’m guessing the inconsistency might be due to some backlash in the drive
axes. Have you weighted the mount so that you are east heavy, and camera
side heavy?
I never really understood the concept of how to make my mount east heavy. I balanced my mount with all my imaging gear. So how do you make a mount east heavy ? Let’s say you are pointing north and it’s east heavy, surely when pointing south you become west heavy and make backlash worse.
Also in regards to the camera, how do you mean, side heavy ?
What a lot of people do is simply slide the counterweights further out from
center so that there is always positive weight on the gears. This results
in a slight imbalance in RA so that the teeth of the RA gears are always
engaged against the same side of the worm gear. But as you correctly
stated, if you do it this way then when you do a meridian flip the backlash
will also flip to the other side of the gears/teeth. But after the flip
the gears should stay engaged on the same side of the teeth again.
The best thing would always be to have the mount slightly weighted to the
east. What I did when I had a G11 was loop a cable FROM the east side,
OVER the RA axis, and attached the cable around the counterweight shaft.
Then on the east end of the cable I attached a 5lb weight. What this does
is “pull” the RA axis always toward the east no matter where the scope is
pointing.
What I meant about being “camera side heavy” was to simply slightly
unbalance the scope in DEC so that there is positive weight on the DEC
gears in the same manner as the RA above. I found it beneficial to have
the scope either slightly nose heavy or camera side heavy.
Hi Joel, many thanks for the clarification on the balance side of things. I guess there is a lot to be said about the benefits of a direct drive mounts where you don’t have to worry about such issues as backlash.
I would kill for something like a ASA mount, and to this day I don’t understand why all mounts are not direct drive as they must be simpler to design and build if they don’t need to worry about manufacturing precision worms / gears etc and just have have to design around a motor. Using gears / worms seems so old school these days.
Just noticed in the release notes for 2.6.0.8 that ir refers to Offset, as per copy of release notes below where it states “Removed Offset2 Telescope Sync option”
I knew i had seen something relating to “Offset” with ref to telescope Sync options. What is this offset / offset2 in regards to Sync ?
2.6.0.8 Changes:
Removed "Offset2" telescope sync option, but kept the logic for it and assigned it to the "Offset" selection. The behavior that was used with "Offset" has been removed. If you have sequences or profiles that were using "Offset2", "Offset" should automatically be selected for you. We realize that there are still known issues with this method (should work for most), but releasing this way is still preferable to a pretty nasty bug in 2.5.1.17.
Don’t use the offset options unless you need to (and you probably don’t). We typically recommend NOT building a model if you don’t need to. I’d really only recommend building a model if you have a permanent setup, other than that you’re just wasting time building a model that you could be imaging.
Tips for getting centered accurately and quickly.
Use Slew and Center options in the target settings. Scope will slew first and then center. So you’re doing the centering closer to your target.
Use blind solve failover. If your first slew is really bad this will save you.
Set the Centering to use multiple iterations. 3 is a good starting point. But more is ok too. Generally I only need 1, sometimes 2, rarely 3. But higher is generally better as SGP will just keep trying rather than failing.