Diffraction Spike Focusing

Id like to take the time to show 1 method of focusing i always use.
It is diffraction spike focusing.
There are many focusing aids on the market but i prefer this devise as it has never failed me yet.
Ive played with different masks including several versions of the Hartman mask design
and have always returned to my design for focusing.
The size of your telescope will depend on the size hoop used.
For my Meade LX200 classic 10 inch i used a 12 inch embroydery hoop.
Measure your scope opening and add the appropriate diameter to be sure it will fit correctly.
ex. for a 8 inch scope use a 10 inch hoop.
for a 10 inch scope use a 12 inch hoop.
for a 12 inch scope use a 14 inch hoop and so forth.

After you choose the appropriate hoop you will need 2 pieces of wood or similar material to make your spikes.
Experimenting on my 10 inch ive found that the spikes worked best at 2 inches wide.
Cut your spikes to length and glue them to the hoop creating a perfect x in the center.
Now we have a nice diffraction spike mask made to use for the perfect focus.
Place the mask over the telescope and point to a bright star,
orentating it so its not parallel to the chip
making sure the spike pattern goes from corner to corner of the imaging chip not up and down.

Now you will want to center a bright star on the CCD chip and hit the auto contrast setting and use a one second exposure.
You should end up with an image looking close to this.

The next step will be to adjust the white point of the histogram to the left to raise the brightness
and adjust the shadow to about 4 to 6. This should give you an image close to this.

As youi will notice the stars have holes in them and the mask gives you eight spikes.
Adjust focus until spikes come together

You will notice in the next few images as you get closer to focus the spikes will become one.

When you have the spikes lined up like in above image, You have the perfect focus.
Remove the mask and start imaging.

I hope this helps out your focusing problems.

Happy Imaging
Mark Sibole