Last time I was out I wanted to continue on with a project.
So I open up an image through SGP and rightclick and plate solve. Then I use that information to slew and center and take my first shot, discovering that the center of the image is not near the center of the image I platesolved. I tried and tried - to no avail.I finally had to resort to nudging.
My scope was sitting on one end of a losmandy bracket, perpendicular to its longitudinal axis, and I had a dslr mounted on the opposite end of the bracket, so the imaging scope was offset by 6 inches from the mount. Could that have been the reason for platesolving issue?
Yes, and the image appears to be correct except that it is moved to the
side, which is why I suspect it could have to do with scope being off axis
from the mount.
Well of course you want to make sure that everything is well balanced. That’s one thing. Let me ask you this. Are you setting up your gear each time or does the mount live in an observatory? If you’re setting up each night make sure that you clear out any sync data in eqmod before you start for the evening. It will make your mount slew incorrectly if a bunch of snyc data is in there and it does not apply anymore. Also I always start in the park position for the first slew.
My mount is on a tripod and it gets moved around. In case of this anomaly,
the image I used to platesolve was taken from home and the images I was
trying to get was from a new location. I don’t know how much difference
location would have made.
I do clear sync data before syncing, and as I was testing it using a
planetarium software, it looked like the mount thought it was in the right
place, except the image did not support that.
Yes, J2000 is what I use, and I am pretty sure that I checked that as well.
So you are thinking that being off-axis we should still be able to
platesolve to the center of a reference image and expect the scope to be
pointing to that center, right?
Yeah I would imagine it could get it there but keeping it there might be a problem. I’m not positive on this, I need to dwell on it for a little while! ha ha
I do know this though and that is if I have sync points from last nights imaging still sitting in EQMOD and I broke it down and set it up again that it will make my mount struggle to track. SGP will plate solve and get it on target but those erroneous sync points will make my tracking terrible.
I don’t even star align anymore. I just pull up an image from the prior night, plate solve it, save it as the target and click on center. After that I just bring up guiding and start imaging.
Yes, that is my explanations - the difference of 6-inches, some say is
negligible, but my pictures say otherwise.
I religiously clear EQMOD since I struggled a lot to learn solve and sync,
and a lot of the struggle had to do with these various EQMOD settings and
residual data.
I never star align - with plate solving I either have the address or I get
the address by using another image. And that last one was my first time
doing it so I am not sure what forces were in effect.
You do know how far stars are away do you? A very long way. So far that a difference in position of hundreds of millions of kilometres hardly matters. Six inches is totally negligible.
It’s not the different position that matters, it’s that the two scopes are pointing in slightly different directions. Like the way that a finder has to be adjusted so that it is aligned with the main scope.
Chris, yes, I had some idea about stars being far away.
Ed, I don’t get Chris’s message. What is it that you set to 50 pixels, and
do you think that I need to set anything especial in order for this to
work? Are you only talking about your guiding?
No, not guiding, plate solving to move the telescope.
Yes, you need to specify how close to the target coordinates you wish to point the telescope during plate solve moves. If you specify 0 pixels it will probably take many plate solves I found 50 pixels is usually good enough to get the target towards the middle in a satisfactory manner, but I do photometry where exact centering is not needed.
In Equipment Profile Manager: My settings—
Equipment profile >>Plate solve>>”Attempt to center” --> 5 “times” --> “until error is les that” 50 “pixels (I don’t have a rotator)