What focus method do you use for planetary imaging?

[Stonius]

As far as I can see, there are three options;


1) slew to a star and run a V-curve autofocus routine then slew back to the object. For me that would mean getting pin-point accurate gotos setup, and making a Voyager Profile that is just for focusing a planetary camera (I don't think Sharp-cap or Firecap have autofocus routines? Helper tools, yes, but I've never found them to be that useful. Maybe I'm missing something?).


2) Bahtinov Mask. Again, this would work best on a star, as planets are a disc.



3) Just eyeball it. With seeing going in and out, I find this method really difficult to gauge because you're comparing flashes of good seeing with another moment that happened a few seconds ago. Was the previous flash more in focus than the one just gone? Who knows?


What would be best would be some kind of in-situ tool. I've just downloaded Firecap's FC edge plugin. Maybe that'll work better. I see sharpcap has some tools including fourier detail detection, and edge contrast detection. Maybe I should switch?


What are your experiences? I'm curious how others approach this problem.


Cheers Markus

[glend]

Assuming your equipment is temperture equalised, a Bahtinov mask works fine, your can focus on an adjacent star in your field of view, or nearby. Don't over complicate it, which many imagers do.

[multiweb]

3 for sure. Bahtinov Mask is too coarse. With experience you'll be able to judge your focus based on features on the planet and/or the limb. Jupiter is quite easy. Especially if you have moons in the field. Saturn the rings and cassini division are there for that. Mars can be a little tricky but with time you know what to look for. Most capture program can stabilize the planetary disc so you don't have to follow a jumping ping pong ball.

[Merlin66]

I agree with Marc.
For solar imaging I use FireCap and #1 eyeball.... aided by a SW focuser motor.
Seems to work well for me.

[DarkArts]

Nearby bright star and Bahtinov mask for me. I've tried eyeballing, but usually can't quite get it.

[Tulloch]

Use the planet - dial up the gamma to increase the contrast on the screen (and increase the brightness so you can see the planet again), then use the clouds on Jupiter, the Cassini division on Saturn, or the edge of the disc on the others to focus on.

I usually spend at least a couple of minutes before capturing a video just moving the focus knob a little bit forward, a little bit back, too far forward, too far back, wait and watch for a few seconds, move it a little more etc etc. After a couple of minutes, I know what I should be looking for to get the best focus I can, given my equipment and the seeing at the time. That way I know I'm at the best focus for the capture to come.

Since I don't have an electronic focuser, I have rigged up a piece of pipe insulation and one of my wife's long hairclip, which allows me to push forwards and backwards without introducing vibrations in the mount. An image of this arrangement is shown in this link.
https://www.cloudynights.com/topic/707728-focuser-or-not-focuser/?p=10194236

In conjunction with Firecapture's Auto-align button, it holds the planet rock steady while I am focusing.

Andrew

[Stonius]

Thanks for the insight guys. I just find it difficult because the focus is *so much more critical than for deep sky (as well as needing great seeing and spot on collimation). I'm not really sure I trust my own eyes, TBH.


I have a new scope coming that might make things a bit easier - a 16" Goto Dob. I'm hoping to get better contrast than my RC 10. We'll see. I'm determined to nail some planetary photographs at *some point.


Cheers M

[Tulloch]

My dream scope - hope it works out for you. The next couple of years will be the best for planetary imaging for a long time ...

What other bits have you got?

[Stonius]

I've got a Hubble Optics 16" F5 coming. I'm hoping it will solve several issues for me.



One is that I don't really have a good scope for planetary work. Of my other three scopes, the esprit 120 loses too much light before the appropriate image scale can be achieved, the RC10 lacks the required contrast (it's a deep sky astrograph, really) and my current 16" is manual and doesn't track the planets.


I also realised that I like the looking at stuff more than the process of star-hopping and finding it. Plus I won't have to adjust the scope to keep the object in the field, which I'm hoping will be less distracting.


I've got a bunch of barlows and powermates to get the right image scale, TV 2x, 2.5x and 4x but I mostly use an ES 3x at the moment because that's what I need and TV don't make one.



Cheers


Markus

[JA]

Hi Markus
I did see a video on Planetary astro that covered a lot of ground and spoke specifically also about focus. I will have a look through my history and see if I can recall it to post it here.

EDIT (that was quick, found it)..... Longish Video Presentation 55min - Wonderful jupiter Image at ~12:20 onwards followed by camera/focusing discussion, a few years old now also lovely animation of Jupiter at ~41min
https://www.youtube.com/watch?v=puoh1ikzonA&t=836s

Best
JA

[DarkArts]

Damian Peach: "... you get to kind of know when the telescope is in proper focus just through practice in using that focussing system ...".

I obviously need to improve my practice! :rolleyes:

[The_bluester]

I reckon you could do it with Voyager if you have that set up. Slew using the planetarium software to the planet, then in Voyager plate solve and sync, back to the planetarium to re slew back to the planet from wherever the fist slew put it. Once you have the planet centered that way, you could tell Voyager to go off and do a robostar focus, at the end of which is should plate solve back to the planet again, disconnect in Voyager and connect with whatever software you use

[Stonius]

Thanks JA, that was a great presentation. I watched a lot more than just the bit about focus.

[Tulloch]

Here's a few tutorial video about planetary imaging that also might help. Ignore the bit when Steve recommends the Celestron NexImage 5, these are a few years old :)
http://planetaryimagingtutorials.com/

[Startrek]

Method 3 eye ball it and use the electronic focuser
Takes time , with the planet jumping around on live view but you develop a skill set to improve your focus the more you do it
Like everything experience helps a lot

[Tulloch]

I'm a bit puzzled by your comment with "the planet jumping around on live view", how are you capturing your planetary images? Or are you using your Canon through BYE for planetary captures?