I am working on a Sequencer focus routine for my new Esprit 100 and was wondering what step granularity anyone has used to success? The routine is used periodically during the night to refocus. My assumption is that the focus will change over time as the temp changes and this routine will hopefully bring it back. It needs to work if the focus has moved in or out.
When called the routine will move "out" about 300 steps then start going "in" with a step size of 50 and run for 20 steps. Is this granularity small enough to get a good focus? This Esprit seems to focus well and I can get a Multistar FWHM score in the 2s easily when using the autofocus routine but I usually run at least two focuses back to back and can manually narrow down the focus window.
In this routine I want one shot at focus and back to imaging so I need to have the start position and granularity correct I believe to get a spot on focus. Another option is to do two focus routines back to back with the second routine having a much smaller step granularity and a much closer "out" starting point.
Any suggestions are appreciated. Thanks
What granularity do you use in the Sequencer focus routine
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Re: What granularity do you use in the Sequencer focus routine
Hi,
the difficulty here is that the answer to this question will depend both on how big the step size is with your focuser (does it take 100 steps to move 1mm or 1000? or 5000?) and on the telescope in use (how far off focus do you need to be for the misfocus to be pretty obvious in the focus score graph).
So, the thing to do is to run a manual focus scan and judge how many steps in total does it take to go from clearly out-of-focus on one side through in focus to clearly out-of-focus on the other side - far enough out of focus each side that the curve in the graph is clear and fairly smooth rather than being noisy. Maybe that will be 500 steps. You then need to divide that 500 step range up in the right way to get just enough steps without making the number of steps so big that the focus scan takes ages. 7 is the absolute minimum, but 10 to 15 is probably a safe range. As long as the curve is fairly smooth then the way SharpCap interpolates the curves between the measurement points means that the best position will be found even if it isn't right on a measurement point.
cheers,
Robin
the difficulty here is that the answer to this question will depend both on how big the step size is with your focuser (does it take 100 steps to move 1mm or 1000? or 5000?) and on the telescope in use (how far off focus do you need to be for the misfocus to be pretty obvious in the focus score graph).
So, the thing to do is to run a manual focus scan and judge how many steps in total does it take to go from clearly out-of-focus on one side through in focus to clearly out-of-focus on the other side - far enough out of focus each side that the curve in the graph is clear and fairly smooth rather than being noisy. Maybe that will be 500 steps. You then need to divide that 500 step range up in the right way to get just enough steps without making the number of steps so big that the focus scan takes ages. 7 is the absolute minimum, but 10 to 15 is probably a safe range. As long as the curve is fairly smooth then the way SharpCap interpolates the curves between the measurement points means that the best position will be found even if it isn't right on a measurement point.
cheers,
Robin
Re: What granularity do you use in the Sequencer focus routine
"SharpCap interpolates the curves between the measurement points means that the best position will be found even if it isn't right on a measurement point."
That was the information that I needed. Thanks
That was the information that I needed. Thanks