Focusing tip

I was imaging the moon last night, and I came across a neat little trick, maybe you guys know this, maybe not.  As you know, I'm using an f5.5, 127mm refractor.  The focusing is quite critical with such a fast lens.

When I image the moon, I use an el-cheapo Meade 2X barlow.

What I did last night to get an almost perfect focus was to focus as best I could normally.  then I de-focused just a wee bit on the inward side.  I then loosened the camera to barlow screw and slid the camera out of the barlow very carefully, and I was able to get a much finer focus.  The barlow acts something of a "vernier", making the focus a little less touchy.

a useful tip for us guys using fast scopes......which kinda makes sense, as a barlow actually increases the focal length by a factor of X, which would increase the acceptable focus adjustment by a factor of X.

I've done that trick on the 70mm which is a bit slower too.  Also, as you slide the camera out of the barlow, you get a little bit more magnification.