Focus tools

[Ronald]

Ronald from California
How do I adjust the black level and noise reduction to achieve the green bars in the graph before the actual physical focus? With the fwhm is it done over the roi or an area excluding the roi and after the best score is achieved do i reset the graph and do a mechanical focus? Thank you for any help

[chongo228]

https://docs.sharpcap.co.uk/3.2/#Settin ... ck%20Level See the section about FWHM black level.

As far as noise reduction I usually don't mess with it. I think I have it set to something in the single digits. This will change is you have a non cooled camera or crank the gain up.

If I read your second question correctly -The black level is set over you ROI so that it excludes any faint stars or any other background light. You only want it looking at the star you pick. Don't pick a star that is super bright either. If it's too bright your exposures will have to be very short and focus scores might be affected by "seeing". I pick a medium brightness star and use that. I try to do exposures of a 2-4 seconds. I find the bar graph easier to read when playing with the settings.

You can check your focus with a mask after.....until you are sure you have a system down you should probably do this. I can usually get SC to agree with my mask when the scope is pointing towards the zenith. The atmosphere is thinner and I don't have any light domes to worry about. I have not been able to get consistent results when aiming low....it's close but I can do better with my mask about half the time. I'm planning on sitting down one night in the next few weeks and dialing in my focus method. I'll post in tips and tricks when I do.

Last- don't worry about matching the numbered position too much when comparing SC vs your mask. For example, If you find location 5050 with your mask and then go to the routine and get 5030 as the best result check it with your mask. If the mask shows you are dead on then the difference in 20 clicks is because your backlash isn't set or the focuser slips a bit. A moonlite or Feathertouch will minimize this but not eliminate it. Unless you have a high end focuser you should pick "go to best score" when trying to find focus.

[Ronald]

Hi
When using the multistar fwhm Focus tool , the graph comes out all Green bars at the same level but my scores go down as more stars are detected with the boxes. Is this the normal function for that tool or am I missing something , thanks in advance

[admin]

Hi,


The scores on any of the focus tools will change as you adjust the various settings. That doesn't really matter – the important thing is how they change when you leave the settings alone and adjust the focus. If you are using multi-start FWHM for instance then as the focus improves the stars will become smaller and the score will go down. The graph always tends to show the best values in the greenest colours and the worst values and colours that are more towards the orange and red end of the spectrum. The colour of a particular bar in the graph can change as new readings are added that might be either better or worse than the old best/worst values.

Cheers, Robin

[Ronald]

Hi Robin
Follow up, focus tools working fantastic for me! the proper reducer flattener also helped out tremendously learning patience with the multi-star fwhm helped as well, better mount comes next


CHEERS. Ronald

[admin]

Hi Ronald,

Good to hear that you are making progress – even if it sounds like expensive progress

Cheers, Robin