What’s the best step size for focusing

[Howardk]

I have a zwo EAF and a 9.25” Edge at focal length 1645mm in average seeing conditions

When using the multi star fwhm focus assistant what is a good step size to use?

Is 20 too small for example?

I am getting best focus at around 4.2 fwhm with step size of 50
Is this acceptable ?

I use sharpcap to do the backlash adjustment at 150 steps

[admin]

Hi,

if your best focus comes out to be about 4 FWHM, then the thing to do is to run the focuser from a bad focus position of about 10 to 12 FWHM on one side of best focus through best focus to about 10 to 12 on the other side. See how many steps it is in total between the two end positions - let's say for example it is 1000 steps. Now pick a focus movement step size so that moving a total of 1000 steps will take at least 8 but probably not more than about 13 to 15 separate movements. In this case we would choose 100, so the focus scan would be 10 movements of 100 steps each, giving a total scan distance of 1000 steps.

Taking this approach means that SharpCap can measure the focus over a fairly wide range from 'quite out of focus' on one side through good focus to 'quite out of focus' on the other. This should give a good strong focus curve where noise in the measurements has little effect and reliable focusing. You don't need to take tiny steps as SharpCap will find the best point of the curve even if it didn't measure at exactly the best point.

It's basically impossible to give a correct answer to your original question of how many steps should you use, because the right answer depends on your telescope, electronic focuser, how it is connected, any reducers, etc etc - only someone with *exactly* the same setup would be able to answer that question directly!

cheers,

Robin

[Howardk]

Will try this tonight

[Howardk]

Yup

Got it all working tonight

Best focus seems around 3.2 fwhm

I have average seeing and am at f/l 1645mm so this seems pretty good??