DSLR Focus with a Bahtinov Mask

This is the surest way to go for the inexpensive route! I've read about other methods for people with software and motorized focus, such as FWHM (Full Width Half Max), but a Bahtinov mask is simple to use with simple equipment.

The plastic Bahtinov mask on my DSLR telephoto lens working at 200mm:

Thanks again to Ian Doktor for 3D-printing it! Ask around the club for someone to print you one as a favour, make one yourself, or purchase one. For larger apertures, the slots need to be of different size and spacing but one like this can be used across a range of lenses without losing its basic effectiveness.

For the complete beginner there is a slight surprise. When you look through the camera's viewfinder the image, you can't see the expected diffraction spikes. But you still see the somewhat fainter stars. Use LiveView at 10x, and chances are you still won't see the spikes, instead you'll see a triple star, like this:

Slightly out of focus the side dots skew:

Place the mask with the vertical slots and bar pointing "up" relative to the camera, that way the 3 dots are "horizontal" on the image frame to give you an extra reference.

Take a test picture, then zoom in to confirm the position of the diffraction spikes. In focus the horizontal spike will be smack through the middle of the X, like in the middle image below left.

I use a magnifying loupe (variants can be found at coin and stamp stores).

Better yet, I have since moved to a phone app DSLRcontroller ($10.99) which means I can focus electronically without vibrating the camera turning the focus by hand.

While the newest camera models can be controlled wirelessly, anything older than a Canon 60D must be wired (as shown above). Works on Nikon, Sony, etc.