Hi,
I am using a C11 and Starizona Microtouch focuser. I find I am balancing the step size with focus range. If step size is too big, get funky points on the graph. If step size is too small, often “just” miss the focus point.
For instance, the points on the right side of this graph represent really out-of-focus stars:
A bigger step size might have captured the curve better on the left, but the out-of-focus stars “look” like they are in better focus.
Also, I often get this, even when it is already pretty much centered on the focus point (ie. two ends of graph fall off quickly):
Appreciate any suggestions to improve the settings. I can supply AF packs if that would help.
How out of focus are the stars when you are at either end of the curve when you get the ‘drop-off’? Are they massively out of focus and hugely donut like?
Also, how in focus are you when you start the focus routine?
Hi @PhotoGav,
Thanks for the response. Here is current focuser “Other” settings:
And yes, the points on the ends are significantly out-of-focus, and donut-like.
Hmmm, just noticing that my focus exposure seems to have gone back to 1 second. I thought I had set that to 8 sec last month. Will have to experiment with that some more, next night out (maybe tomorrow night) - that could be a significant contributing factor.
For my setup, HD11, my step size is 200, backlash=1,200 and minimum star size is set to 6. I focus at 4x4 @ 5 seconds. This is with using the Rigel N-Stepper primary mirror for focusing.
Your results may differ. May need to try different settings. As Frank said, start close to focus helps.
I find it interesting that the out of focus regions you point out are the regions where the HFR is the smallest. You want the HFR to be minimized.
On my EdgeHD11 the settings are: 7 data points, 100 step size, 10 sec exposure. Backlash compensation of 300 IN. I have the Starizona Auto Focuser with Feathertouch focuser. These settings are with the 0.7x FR in place. They work very well for me.
Those small HFR values are artifacts of not reading the donut size correctly. I don’t think there is a real need to measure donuts properly because all you have to do is stay close enough to focus that they never happen.
You can tell the real part of the plot because it is making a nice parabolic curve near focus.
As all say above, try reducing your step size to 100 or less and ensure that you start the night pretty much in focus (a quick exposure to ensure that stars are points not donuts is good enough!).
Good to see that you have the backlash set up - that is essential.
Good luck and it looks like you are very close to an optimal set up.
To show solidarity with a fellow SCT user here’s a AF run the other night with my C14 with Lakeside Focuser on the primary, working at about F6.5… After many nights of testing I’ve settled on 100 steps + 450 backlash in. I use 10 secs exposure with Lum filter - I’m under bright 53 degree north skies at the moment + very light polluted - so longer exposures only way.
here’s a AF run the other night with my C14 with Lakeside Focuser on the primary, working at about F6.5… After many nights of testing I’ve settled on 100 steps + 450 backlash in. I use 10 secs exposure with Lum filter - I’m under bright 53 degree north skies at the moment + very light polluted - so longer exposures only way.