I am having a devil of a time trying to get my field totally flat. now i am using a zwo asi183mm pro with the william optics z73 with flat 73r and a filter wheel. it said to adjust the ring back 1.8mm for a camera with 17.5mm backfocus.. i did and no matter where i adjust it, it is always seeming to be not flat. Am i needing to add or remove distance if the stars are flying away in the corners? or is it just basically trial and error until i find it? Thanks for any tips/hints !
need a little help with William Optics Flat73R
Hi Richard,
for getting the right distance between the flattener (or reducer) and the sensor i use a trial-and-error-approach. First, calculate the desired arcsec/pixel-scale for your gear using astronomy.tools. For your gear the desired total focal length will be 344 mm (430 * 0.8 ). The size of your pixels is 2.4 um. That should result in a scale of 1.44"/pixel. Now you just take a picture (a few seconds) of any part of the sky and upload it to nova.astrometry.net (or plate-solve it by any other tool). The website (or your tool) will tell you within a minute or so what the actual pixel scale of your image is. If you are at 1.44"/pixel your spacing is right. If not, add or remove a spacer-ring between flattener and sensor, take an image, upload it to nova.astrometry.net and check the scale again. Redo this until you hit your pixel scale. With this approach you can reach the right spacing fast and you can be sure that you did anything right - once you reached 1.44"/pixel. Hope that helps!
CS Michael
for getting the right distance between the flattener (or reducer) and the sensor i use a trial-and-error-approach. First, calculate the desired arcsec/pixel-scale for your gear using astronomy.tools. For your gear the desired total focal length will be 344 mm (430 * 0.8 ). The size of your pixels is 2.4 um. That should result in a scale of 1.44"/pixel. Now you just take a picture (a few seconds) of any part of the sky and upload it to nova.astrometry.net (or plate-solve it by any other tool). The website (or your tool) will tell you within a minute or so what the actual pixel scale of your image is. If you are at 1.44"/pixel your spacing is right. If not, add or remove a spacer-ring between flattener and sensor, take an image, upload it to nova.astrometry.net and check the scale again. Redo this until you hit your pixel scale. With this approach you can reach the right spacing fast and you can be sure that you did anything right - once you reached 1.44"/pixel. Hope that helps!
CS Michael
Helpful Supportive
Thank you Michael. I believe I just figured it out right after i sent this, I need to have the 55mm backfocus from the edge of the reducer to the sensor first before i start adjusting… it just popped into my head …. so tonight ill be adjusting accordingly. once again.. thanks for the info
Clear skies Richard
Clear skies Richard
I'll keep my fingers crossed! Keep us informed!
it worked like a charm… now have a flat field across almost the whole field, only a little flying away in the very corner of one corner. I thank you again for the help.
Good news! Glad you made it!