PixInsight Forum (historical)

PixInsight => General => Topic started by: Seldom on 2020 February 24 10:03:14

Title: Fits Header Focallen doesn't agree with my scope specs.
Post by: Seldom on 2020 February 24 10:03:14

I'm imaging with an NP101is.  Sometimes with a .8x Televue field FL reducer.  Specs say the base focal length is 540mm and the reduced focal length should be 432 mm.

I'm trying to recall if I used the focal length reducer on an image I took with a Canon60Da but after I run a Photometric Color Cal on the original image FitsHeader reports a focal length of 480mm.

When I'm imaging with an ASI1600MMC FitsHeader reports a Focallen of 443mm when I use the .8x focal length reducer.

Thoughts on how to interpret the 60Da focallen would be appreciated.

Title: Re: Fits Header Focallen doesn't agree with my scope specs.
Post by: Andres.Pozo on 2020 February 24 11:39:17

There are at least two possible problems: You could be setting a wrong value for the pixel size of the camera or the focal reducer is not at the right distance.

Title: Re: Fits Header Focallen doesn't agree with my scope specs.
Post by: Seldom on 2020 February 24 12:22:08

Thanks, Andres.  I know I had the focal reducer located wrong back then.