Plate solve image scale


Hi all, just a query about plate solving!!
As I calculate my image scale, I get 3.39arc sec / pixel.
O.k so when I try to plate solve a recent image, plate solve fails due to the scale hint being incorrect at 3.39…odd…
However; after an astrometry check, it shows the image scale as 2.85…if I use this in the hint box …success :smile:
But here is my issue, the hint box will not retain the correct image scale, reverting to 2.1arcsec/pixel despite changing it in the scope configurations tab…
Anyone any ideas how the scale hint box works??



Ray, there are several ways to plate solve in SGPro and your description does not make it clear which workflow you are having difficulty with…

Please provide concise steps.


Ahh: o.k. Ken, thank you for replying…i use what i assume is a pretty STD method in that I use a local astrometry search! for a recent image I’ve taken.

By using the gear icon I select my image and then solve, I don’t normally blind solve…I expect and usually find that it solves within 20sec…fine.

It’s just that I have to keep changing the hint from 2.1 arcsec/ pixel to the correct image scale…if I dont, it keeps failing.
Not a major issue, just trying to understand it.



Well, when you open an image in target settings, it will grab the scale from the image’s FITS headers. If your image does not have SCALE in the headers, it means that SGPro did not have information to calculate scale when the image was captured.


Ahh o.k. I understand that!

Just clarify for me Ken…when I take an image, does the Scale for the fits come from my settings???

In other words, if I put in an incorrect scale on my telescope tab, then the hint box will populate with that incorrect hint taken from the image.

Sent from my Hudl

Ken wrote:


No we do not trust scale input by hand, we will use these for hints in the solve of real time images, but that’s about it. If you want scale in your light images, you must have gone trough some sort of solve and sync process prior to capturing the image. You can do it manually or it will happen automatically as part of the automated centering process. We only write scale to the headers if it came directly from a solver.


O.k thanks Ken

Sent from my Hudl

Ken wrote: