Focusing on a star vs. a planet

[Dirty Harris]

I am seeking any help on focusing on a planet vs. a star. I understand that the best way to focus of course is to go to a nearby star and use the FWHM feature in frame and focus. Well that works well for the star or maybe nebula and galaxies, but when I slew back to a planet say Jupiter then I am a bit out of focus. Just enough in fact, that when I run the video through Registax-6 and come to the wavelets/sharpen sliders and slide them all the way to 100%, there is very little if any improvement in the image. Oh you can tell that it's Jupiter with it's equatorial bands and others near both poles, but it's just a bit fuzzy or out of focus.

 

Now I know there are many variables in the equation for focusing. Seeing, transparency, jet stream, camera noise, light pollution etc. I can account for all of these, even the noise can be smoothed out, but the blasted image is still just fuzzy. And it's so frustrating because you can tell it's soooo very close to being great, but falls short, or long?

 

I was wondering if instead of focusing on a star, that maybe I should be focusing on the planet itself right from the start and use the same FWHM mode in frame and focus? This eliminates my subjective focusing by eye, and instead uses BYEOS objective.

 

Here is my set up- CPC/SCT 11inch Celestron fork mount on a wedge polar aligned, and go to sky aligned, Crayford dual focuser to eliminate mirror flop, dew shield on and warm, using a Canon 1100-D( T-3 Rebel) dslr camera, at f-10 with a 2.5x Televue powermate barlow. Approx. 20 fps video that runs about 2minutes in length. Capturing in BYEOS Avi format.

 

I welcome any suggestions and eagerly await some wisdom from anyone on this focusing subject. Thanks.

[Jim]

I haven't tried but would using a Bahtinov mask with one of Jupiter's moons be possible?

 

Jim

 

[astroman133]

I have never heard anyone complain that a minor slew causes a focus shift.  I would use the Precise Goto function of the NexStar hand controller to slew to a star near your target (Jupiter), focus while locking down the mirror when you are sure that the external focuser can reach critical focus and then complete the slew to Jupiter.

[worcspaul]

Could it be that because Jupiter's so big, its curvature means you're not able to get pin-sharp focus across the entire disc?

 

(See http://www.damianpeach.com/jupiter.htm for examples)

 

 

[Jerry_K]

I have never heard anyone complain that a minor slew causes a focus shift.  I would use the Precise Goto function of the NexStar hand controller to slew to a star near your target (Jupiter), focus while locking down the mirror when you are sure that the external focuser can reach critical focus and then complete the slew to Jupiter.

 

I agree with Rick 100%. I always use Precise Goto for every DSO I image and never had a problem with short slew throwing target out of focus.

As far as curvature of Jupiter goes it is natural that center will be sharp and edges will be fuzzy, After all center is perpendicular to surface of the Jupiter whereas edges are at shallow angle and light has to travel through thick layer of atmosphere. No problem for Moon because it doesn't have an atmosphere.

That's just my opinion,

Jerry

[PoppaChris]

Instead of using FWHM in "Frame and Focus" to focus on a planet or the Moon, try Standard Deviation focusing.  Just remember that the bigger the number the better the focus.  Just the opposite of FWHM.

[admin]

Hi David, I will move your post in the BackyardEOS forum.  You will get more traction there.

 

Guylain