Recently I discovered a - at least for me - new technique to focus.
I assume it only works for reflector telescopes (Newtonians with spider vanes), armed with a long exposure camera (eg SC or JG modified).
Other types of scopes can use a cross made of Chinese 'chop sticks' or similar material: fasten this at the sky end of your scope and you get your diffraction spikes!

My procedure: aim your camera at a relatively bright star and focus in the normal way.
Sometimes you immediately get nice diffraction spikes, other times you have to increase the exposure time to get those spikes.

The spikes themselves are nice to see - like from a fairy tale - and I use these for fine focusing!
Diffraction spikes focusing goes BEST when selecting 'Zoom 200%' in K3CCDTools and with Long Exposure it simply is magnificent.

Needle sharp diffraction spikes.

The spikes must be sharp as needles; when you have achieved this both your collimation and your focusing are perfect.
Of course focusing the telescope goes best with an electric focuser: I use my home made one.

I find this diffraction spikes focusing method much easier than trying to get very faint stars on the preview screen, or to use a Hartmann mask with whatever holes.
And after focusing in the 'diffraction spikes' style just aim your telescope at the target you had in mind, without changing the focusing, of course :-)

Here you see the diffraction spikes masks I made for the successors of my TAL-2M:

LX200 - Diffraction Spikes Mask LX200 - Diffraction Spikes Mask

This is the dew shield I made for my William Optics Zenithstar 80 ED II APO.
Please note the metal pins in the dew shield: they create diffration spikes, which are great for focusing and also look nice in the image.

This is the diffraction spikes mask I made for my William Optics Zenithstar 80 ED II APO.
In the plumbing department of my local DIY shop I bought a plastic ring which nicely fits in the dew shield I already made for my ED80.
To generate the diffraction spikes I used thin fishing line which gives more delicate spikes than the metal pins I used before.