Image of the day

Captured by
Erwin Forbragd

Leo Triplet

My Account

New to Astromart?

Register an account...

Need Help?

Collimating a Mewlon

Started by Hans Tucker, 05/17/2012 10:21AM
Posted 05/17/2012 10:21AM | Edited 05/18/2012 09:46PM Opening Post
Has anyone come across a easy procedure for collimating a Mewlon 250 that they could share or point me to.
Posted 05/27/2012 12:50PM #1
Hey Hans,

Easy? Indeed not. Suffice it to say that collimating a Mewlon can be a challenge. However, the best source is calling TNR and talking to Fred.

After facing a similar endeavor, I too called upon Fred's expertise. I'll paraphrase most of the discussion:

Collimate in the daylight -- Place the OTA on a bench at sufficient height so that you can look into the OTA from the front at eyelevel.

Cut a piece of cardstock 12X12 inches square and then cut a 3/4 to 1 inch hole in the center. Use the card by holding it up to your eye, move it back and forth or adjust your viewing distance from the OTA so that the card blocks most of what you can see and the center hole shows only the OTA opening. This allows you to align your eye more or less to the OTA optical axis.

Holding the card in place as described, you will see the secondary shadow more or less on the primary mirror and two sets of secondary spider vanes. One set is the actual spider vanes and the other set is the reflection of the spider vanes in the primary mirror. Note the position of the of the two sets of secondary spider vanes. In a perfectly collimated scope, the two sets of vanes will be perfectly aligned over top of one another appearing as a single set and the shadow of the secondary will be centered in the concentrical reflection of the primary giving a kind of donut appearance. This is your objective for collimation

If the OTA axis is misaligned/out of collimation, the spider vanes will not appear as a single set and the secondary shadow will not be centered in the primary mirror's reflection. Adjustment is required at this point using the three sets of correcting screws each paired with a push/pull screw at the back of the secondary mirror. Please use the attached, rather crude drawing provided by Fred of TNR. In two following posts I provide Takahashi's collimating instructions.

Once adjustments are made in the daylight, very close collimation is achieved sufficient for most applications including astrophotography. More precise collimation can be achieved using an artificial star or Polaris. These being relatively fixed points of light. Usually, you don't have to resort to this level of adjustments.

Attached Image:

reconair's attachment for post 144272

Scott Busby
A.K.A. Reconair

Carpe Noctum

Mortal as I am, I know that I am born for a day. But when I follow at my pleasure the serried multitude of the stars in their circular course, my feet no longer touch the earth.
- Ptolemy,c.150 AD
Posted 09/16/2018 08:13PM #2
Fred at TNR was instrumental in providing the information about collimating my Mewlon years ago (2005),  though as long as Ive used it, and traveled with it,  I have checked it several times and found it to remain solid.