Focusers:

To accomplish good focusing there are a number of tools available, Auto focusers, motor focusers and manual focuser.

Auto Focuser use a program to  control the motor focuser by sampling the image and determining if the focus needs to  be adjusted. This sometimes is needed during long imaging session where the ambient temperature varies greatly. Unfortunately these devises and associated software can get rather pricey.

Then there is the motor focuser. This device usually replaces the focuser that  comes with  the telescope or controls the existing focuser with a small motor.  The great benefit in having one of these devices is that you  do not need to  touch  the telescope to  focus it. Simply touch  a button to  drive the focus in or out. Touching the focuser with your hand causes all kinds of jitter which  has to  quiet down to  see if you  actually  are turning the thing in the right direction.  I feel that  a motor focuser is a must for astrophotography.

The manual focuser is what you  usually get  on the scope when you  buy it and requires you  to  grab the knob of the focuser to make any adjustments. OK for visual observation but a real hassle when using a camera to  watch the focusing process.

Focusing Aids:

Focusing a camera while doing normal photography is rather simple if your eyesight is good. But focusing a star or other dim objects in the night sky can be challenging at best. To  assist us old folks in getting good focus we use focusing masks . Probably  the most common is the Hartmann Mask.

This mask usually consists of three holes or triangles cut out of some material and placed in front of objective lens or opening of the telescope. This mask causes spikes on bright stars and the object it to  get  these spikes clear and aligned across from each other. This is sometimes easier said than done. IF you  want to read more about the Hartman mask click HERE. If you  want to  create a Hartman mask, this LINK will get you  to  a mask generator that  you  can customize for your scope.

I have been using a Hartman mask for a while until I found out about a new mask designed by a Russian named Bahtinov. The Bahtinov mask uses a series of slits, instead of holes or triangles, that  generate an spikes around a star that resemble an X with a line thru it.

As you  adjust  the focus knob the center lined moves up  or down depending on the direction that  you  are turning the focuser.

When the center line is in the middle of the X  your in focus. It's that  simple!
(click on the picture to  enlarge)

You  can buy masks on line for $50  to  $150. But I found it easy to  make myself for peanuts.

This mask is the best focusing tool I have found yet.  The job of getting near perfect focus now takes a few seconds where using the Hartman mask  focus was somewhat  iffy and could take a few minutes

I created my mask out of 1/4 inch foam core board. It is Styrofoam sandwiched between heavy poster board. It's quite rigid and easy to  cut with  a craft knife. It is mounted on an embroidery hoop and easily slips over the front of my  SN8 scope or over the dew shield.
Others had good results in printing the mask on transparency film. You can get that  done at you local office supply store ( Staples, Office Max) that  has a copying service.

If you  are interested in making your own goto to http://astrojargon.net/maskgen.aspx where you  will find a mask generator. I used Firefox to  print out the mask. MS Internet explorer doesn't do a good job. Another program that  you  can use to  printout the resulting mask is called INKSCAPE. It's free and can be downloaded from www.inkscape.org/ .

Have fun!!

Have fun!