Focusing a CCD Camera

Focusing

How I focus the cameras

Pete's Pages

Focusing

I use both types of masks regularly and get on very well with both types. I think the wire type is better for brighter stars and the three hole type seems better for dimmer stars. However both will do the job, so it's just a matter of personal preference.


This three hole mask is made from an old bucket whose bottom just fits around the LX-200 rim. I cut it about half an inch form the bottom leaving a rim that fits around the scope. The hole size does not seem to matter with the focusing, but larger holes can focus dimmer stars with greater ease. The hole in the middle is to take it off the scope so no finger marks are put on the end lens.	The wire mask is just an old fire guard that fits around the scope. I made some prototypes before I had this one, out of wood and card and it does not seem to matter how thick the cross pieces are or how many of them there are. Just make sure they are parallel and at right angles to each other.

The out of focus star through the three hole mask.	The out of focus star through the wire mask.

The in focus star through the three hole mask.	The in focus star through the wire mask.

First I find a star near the object I wont to image. I find it's best to focus every time I move the scope any more than about 4 degrees as the focus tends to loose it's edge because of mirror shift. Then I just put one of the masks on and start to focus via the program I am controlling the scope with. It's a good idea to keep the histogram widow open all the time as the image needs adjusting constantly to get the best results. To find out which way to go, in or out, adjust it a little and see if the stars or lines move apart or not. It's that easy and with a little care foolproof. It's a good idea to make which ever mask you use fit loosely over the scope so as not to disturb it when putting it on and taking it off. It will not fall off as the scope always points upwards.