FocusMax Settings

I now have my V-curves in FocusMax and want to enable the focus convergence. To do that I need to work out Critical Focus Zone (CFZ) and translate that into focuser steps.

CFZ for a scope can be worked out with this fomula:

CFZ(in Microns) = 2.2 x (Scope_Focal_Ratio²)

My RC8 having a focal ratio of 8 gives me a CFZ of 140.8 microns.

That sounds tiny in everyday speak, good thing that I have an awsome high resolution stepper motor focuser.

According to Moonlite focuser manual, 1" travel of the drawtube requires 6135 full steps, wow! that's a lot of tiny steps, 1 micron = 4 steps to be exact.
This leaves me with CFZ = 35.2 steps
So, for the step width in focus convergence setting, I want to set it with  approximately 1/10th to 1/4th of the CFZ step value say 5 steps.

Now to set the various Half Flux Diameter (HFD) values, I'll need to look at my V-curve log.

 The smallest value on the linear parts of the v-curve before it reaches focus seems to be about 6. Increasing this value by 1/4 gives me 7.5(8) to set as Near Focus HFD. This value can be increased by a 1/3 to set as Focus Start HFD, which is 10. The smallest value on the plot is 4.2, increase this value by 1/2 to set as Focus Routine Max HFD, which is 6.3.

Next thing to do is fine tune the V-curve. I'll leave that one for another night....so much too learn...

My Imaging Rig

My current imaging setup: EQ6 mount with EQDIR, GSO RC8, QHY9, QHY Filterwheel, Orion Starshoot Guider, Moonlite Focuser.

I'm hoping to replace the mount in 2011. An Astrophysics mount would be nice.

I'm also working on converting my 9x50 finder scope into a guiderscope, which will replace the white refractor sitting on top. At the same time I should be able to run with one less counterweight.

Moonlite Focuser

Here's the new Moonlite focuser installed on the RC8 with QHY9 and filterwheel hanging off it. I promised to Michelle that this will be the last astro stuff I'll be purchasing 'this' year. Hahahah... Happy New Year!

Just over $720(Awsome exchange rate!!!) landed in Australia, it comes with stepper drive and a USB controller. The flange is manually rotatable and collimatable. Most importantly it shows no sign of flex what so ever.

1st night out I used Bahtinov mask and jog function to reach focus. 2nd night out I fired up Focusmax and followed instructions to run v-curves.

Screen capture shows my initial v-curve runs. To my surprise everything just worked as it automatically stepped through exposures and focuser positions OMG!

There are many parameters to adjust to suit my system, so will need to hit the forums to work out my critical focus zone (CFZ), step size etc..