I am not certain of the true focal length of my telescope to be able to use for the scale calcuation as I bought it used and it has a reducer and a flattener in it. I was told a number but want to confirm. Is there anyway to calculate scale using the image that is created and the pixel dimensions and pixel size?
If you want the most accurate answer, take a pic with a good number of stars and upload it here:
https://nova.astrometry.net/upload
Your image will be “solved” and the site will tell what the actual captured image scale is.
… or put in an estimate, plate solve within SGP and use the pixel scale to work it backwards - same difference from pix scale = 3600 x ATAN(pixel size/focal length)
Thank you.
I was able to get my scale from uploading an image, which is .906. I had to set to .91 in SGPro input only allows for to the hundredths place. I did some back tracking and want to confirm my focal length. If my scale is .906, and the pixel size of my SBIG STF8300m is 5.4 microns. Does that mean the focal length of my telescope is 1230mm. I ask because I was told by the previous owner, with the .67 reducer and flattener, the MM is 1056mm. Seems like this does not corelate to the scale.
Another question I have (if it’s not appropriate for this forum, let me know). I have an OAG-8300 for auto guiding and it’s attached to my SBIG 8300m camera. PHD2 asks for the focal length of the guider scope. The OAG has a .7 reducer incorporated in it. To get the focal length I put into PHD2, do I put 1230mm times .7 or 861mm?
Does that mean the focal length of my telescope is 1230mm
Yes, by my calculations your FL is 1228mm
To get the focal length I put into PHD2, do I put 1230mm times .7 or 861mm?
Correct, you need to put the reduced length in to account for the SBIG OAG’s built in reducer.
Sounds like you are all set!
Ok, thanks.