Focusing on Planets

[groberts]

99% if the time I concentrate on DSO imaging but this time of the year + with Jupiter at opposition, I thought I'd wheel out the ZWO120MC and give it a go.  The first problem is that because I do this so infrequently I can't remember what to do but then I seem to muddle on and with luck end up with something vaguely recognisable.  No such luck last night with Jupiter but hopefully there will be clear skies again in time to give it another try - some hope!

My WO GT81 is not ideal for planetary imaging but OK'ish, however, my usual nemesis focusing seems to be the big hurdle.  Using Firecapture I can get a reasonable size image on the screen - allowing for current poor seeing conditions - but is there some way to improve focus.  I understand that for planetary imaging focus will  come and go due to the atmosphere and Registax will sort out the wheat form the chaff thereafter but even so reliable focusing seems to be near to impossible, or is there a trick I'm missing?

Thanks, Graham         

   

[cuivenion]

You can focus on a nearby star first, or what I do is up the gain and focus on one of Jupiters moons.

[knobby]

I struggle with this too, If I can I use one of Jupiters moons but it does really fluctuate with the seeing.

Next time out I'm thinking of taking several runs and just tweaking focus slightly each run .

[ShrewView]

I also up the gain and try using a bat mask on one of Jupiter's moons, ideally one not too close to Jupiter itself.

[martinl]

I used my TV85 quite a lot last year for Jupiter, should be similar to your scope. What worked best was to temporarily set gamma to 0 for focusing, this creates a contrastier image and allows you to focus directly on some surface detail. If you can’t see any surface detail the seeing is probably not good enough to produce a usable image anyway.

Note that in FC you can create different “filters” with different camera settings. I have an “F” filter with gamma=0 and exposure settings for easier focus and use the “L” filter with gamma=50 and exposure settings for a ~60% histogram for capture.

A Bahtinov mask never really worked for me, but YMMV.

[groberts]

Thanks for the guidance everyone, will give them a try once the clouds part!  

[Owmuchonomy]

As MartinL says a neat trick for focussing is to drop the gamma from neutral (50 in Firecapture) and then put it back when you capture.  You may need to up the exposure a bit whilst you are focusing.  Nothing, as you say, will defeat the poor seeing at lower altitudes I'm afraid.

[kirkster501]

Why can’t you focus on a star?