FX Blue Channel for focusing an achromat

[rcalcagno]

Good day everyone! My name is Ricardo and I live in Argentina. A friend of mine is lending me a cheap Canon EF 75-300 lens to shoot some deep sky images this weekend. I know the images much likely would come up with chromatic aberration, mainly violet rings on bright stars.

I thought about mitigating this somewhat by shooting, say, 50/100 lights with the focus adjusted for the R and G channels, and then another batch of 50/100 lights with focus adjusted on the B channel. Finally, I would combine the R and G channels from the first batch, and the B channel from the second batch. I intend to do so by using FX -> Blue Channel to Mono and then focus the image for the second batch.

Could it work?

Any help is much appreciated. Sincerely,

Ricardo

[admin]

Hi,

blue channel to mono would work for manual focusing, since you would only see the blue image data on screen. Unfortunately you cannot select the blue channel to mono at the same time as SharpCap's focus tools, but some of them do have an 'Image Processing' option in the controls on the left that allow you to select one of the colour channels for measurement rather than the default approach of luminance data.

cheers,

Robin

[rcalcagno]

Ah! Good! My idea for the shots on the B channel, is to take short subs (say, 30s) and check the focus on the B channel each time, stretching the histogram if needed, until a bright star is at a minimum size. Then I would start exposing the subs and check the data on the B channe.l

Will let you know how it goes. Thanks again! Sincerely,

Ricardo.