SHO Change Filter Every Shot?

Depends on how long your exposure is set for. If you are 10 minutes or longer, maybe only 1 shot and then change filter. You can gain time efficiency by using filter offsets if your acquisition software allows it (like NINA). Basically, you can calculate focus runs ahead of time to know the focuser position offsets needed per filter change so you can just blindly run and a filter change will automatically force the focuser goes to the correct position without the need of running an autofocus run with each filter change. Assuming you are using some sort of autofocuser as well.

If the answer is no for an autofocuser and software, then Steven's recommendations are the best. There can be quite a difference in focus range due to thickness of certain filter 'sets' since some are .5 mm in different glass thickness for example.

I don't think it will productive to change Ha-OIII-SII after each exposure.  I do change with each RGB when using MaximDL.  When using Sequence Generator Pro I rotate every 3 to 5 Red, then green, then Blue. But SGP lets  you set dithering to different amounts of subs.  Such as doing one R, one G, one B, then dither and repeat. That way all reds, greens and blues or dithered between each sub.  I see that is the only advantage to rotate between each Ha,OIII & SII.  Howere my RGBs are rather short and dithering between each one can add time.  The Ha, OIII & SII can be 5 to 10min. Dithering doesn't add a large percentage of time.

But,  when doing HOO or SHO, I complete all subs with each filter if I can.  You must consider the moon.  Ha & SII will not be affected at 3 to 5nm.  !2nm can be.  I usually start with the Ha no matter where the moon is, unless I am imaging very close to the moon.  Then I will have to wait.  If it is new moon, then it is best to get your OIII.  Now, this is assuming you will be needed more that one session.

Ones the Ha subs are complete, you can process the Ha image.  It can be nice as image unto itself.  Ones you have the Ha & OIII subs complete, you can process a HOO image, while you wait to complete the SII.  I do another  RGB session just for stars.  Those are short subs and can usually be done in one session. But or best with no moon.  However any gradient in the RGB star image is not a factor since you will only be using the stars and they will not show a gradient.  That also eliminates issues with blown out and  magenta stars in the Ha,OIII or SII images.

Lynn K.