Camera setup/plate solve

Viewed some tutorials, and read the related instructions but I am still left with two questions.

  1. In control panel in the camera tab, setting and specs, one is asked for scale (2.11 in my case)
    Then there is a line for pixels W X H , what value goes here?
    My pixel pitch is 4.3 , pixel area is 18.4um and the sensor size is 22.3 X 14.9 mm?

  2. When plate solving, if one does not have a reference image, can one assume that the image taken after a slew to target can be used as the ref image, plate solved and then used to correct the pointing?

Thank you


  1. This is the number of physical pixels of the CCD chip. So mine for example is 2750W x 2200H (ICX-694 chip).

I’m not quite sure what you mean in #2. If you “slew to” a target it does not automatically take an image. If you mean you slew to a target, start the sequence and get your first image, then yes you can use that image as the reference. Just right click, plate solve the image and then when the success dialogue comes up tick the box to use as the reference image:

After the reference image is set then all other plate solve functions will use that info.

BTW, the Framing and Mosaic Wizard add-on is well worth the cost. Set up your target with that and you’re all set!

Thank you
Looks like my Canon 60Da is 5184 X 3456.

As far as #2 I may not be sure what I mean either. After plate solving ,which I have successfully done, the next action would be to slew to my intended target after plate solving corrects the pointing. My initial slew is with the planetarium software where I find my target and check the meridian ect.
All the tutorials I have watched used a reference image that was an image of exactly where you want to be at the end of the whole deal? That is seldom the case after a slew with the planetarium software, especially at long focal lengths.

I think you’ve got things a bit backward. All plate solving does is tell the mount where it is actually pointed. So if there’s a difference between where the mount THINKS it is pointed and where the ACTUAL pointing is the mount computer will be synced to the ACTUAL position.

I think you may be confusing two different things. You say that “After plate solving ,which I have successfully done, the next action would be to slew to my intended target after plate solving corrects the pointing.” Plate solving has nothing to do with a pointing model. Again, it just gives the mount an accurate position reading. So what I think you are doing is when you first get the mount and equipment connected and running, you are doing a “solve and sync”. This accurately syncs your mount to the position in the sky.

Completely separate from that is centering on your target. If the location coordinates of your intended target are entered, then when you do a “Center Now” SGP will take an image and plate solve it to tell it where the telescope is pointed, then automatically slew the telescope to the target location (coordinates), take another image and plate solve it. If the resulting plate solve info is still some distance away from the intended location, SGP will slew the mount again. This process is repeated until the mount is centered on your target location.

So the bottom line is you need to enter the target location coordinates in the target settings window. There are any number of ways to do this. In the “Reference Data” line, you can find an image on astrobin or flickr and the info will be filled in automatically (if it’s available with the image), you can load an image you have taken and plate solve it to fill in the coordinates, or you can use the framing and mosaic wizard to automatically create the target coordinates.

OR, like I said above, you can load any image in the main window in SGP, right click and plate solve the image, and then set that as the target coordinates (“location” in the target settings window).

Thanks Joel, my verbage is poor.

Yes, I get the syncing to the actual position.

I am using target coordinates imported from SN7, so I am good there.

I will look into the framing and mosaic wizard, more to learn.

I guess the reference image in all the tutorials was used just to get the target coordinates, that is what confused me a bit, as it was not stated specifically.

Thank you for your time and patience.


No problem Peter, we’re all here to help. And yes, the reference image is just to get the target coordinates (“Location”).