What affects focus that I can’t control?

You can’t control the twinkling of stars which causes wander and blurring of the star in the eyepiece.  Wander is the star image drifting/jumping around in the eyepiece by about 3-5 arcseconds.  In a long exposure image wander blurs the airy disk out to 3-5 arcsecond diameter in the image. Twinkling also causes the airy disk to blur out and sharpens up -- the “seeing” changes as the atmosphere twinkles.  At moments of crisp seeing the airy disk is visible, at instances of bad seeing the star is a cottonball

video of Betelgeuse twinkling

airy disk for
out of collimation

airy disk for
in collimation

You can’t control twinkling or seeing, waundering or blurring but you can minimize the effects of the atmosphere by observing stars nearer overhead, where there’s less atmosphere to look through.

What affects focus that I can control?

One effect you can do something about is collimation -- making sure all the mirrors (primary, secondary, diagonal) are perfectly centered and aligned with each other. our Aline collimation tool will help you with collimation. Fortunately collimation is something you only have to check occasionally.

The other effect you can do something about, is turning the focus knob on the telescope, but as we see on the next page, with finesse.


Auto Focus Hardware
DC Focus Motors & Controllers

Motorize your focuser with a powerful 12V DC motor driven by our nFOCUS controller for fine focusing without vibration more...

STEPPER Focus Motors & Controllers

For computer controlled auto focus, motorize your focuser with our 0.10 degree resolution stepper motor and usb_nSTEP computerized interface more...

Focusing & Imaging Software
Autofocusing requires 3 suites of software, although some vendors combine these and other observatory functions.


A consortium of software developers and hardware manufacturers devoted to vendor-independent plug-and-play more...

ASCOM Yahoo Group

Autofocus Software

FocusMax aids astronomers in the difficult task of focusing CCD-based telescopes more...

FocusMax Yahoo Group

Imaging Software

Sequence Generator Pro
Sequence Generator Pro is a powerful image capture application that supports SBIG, QSI, Canon EOS and ASCOM cameras more...

Sequence Generator Pro Yahoo Group

Nebulosity is designed to be a powerful, but simple to use capture and processing application for Windows and MAC OS X. A huge array of cameras are supported for image capture and processing more...

Nebulosity Yahoo Group

MaxIm DL
Complete observatory integration. Controls your camera, autoguider, filter wheels, focusers, camera rotator, telescope mount, and dome. ASCOM compliant more...

MaxIm DL Yahoo Group