collimating a refractor; testing it?

I've put togather a widefield refractor (62mm F4.5), but I am having
trouble verifying it's collimation.

Specifically, I can adjust the objective by several degrees, and cannot
see any difference in the performance. I have tried both a 26mm and 4mm
eyepiece (11 and 70 power respectively), I cannot tell the difference
between way off, and close collimation.

Any suggestions as to what I should see with an improperly collimated
refractor vs. a properly collimated one?

Is it perhaps that I am not at sufficient power to see the
imperfections? Or do I need to be in dark skies to see them?

Mark

Hi Mark,

70 power should almost be enough to see some collimation effects. At
f/4.5, collimation would probably be more crucial than at slower f
ratios. Mainly, I would think that you would be looking for round star
images inside and outside of focus. I don't know how well versed you
are at star test collimation, but tell-tale signs are coma and/or
astigmatic star images. Star images that are sharply focused should
have a dot-like star, (also called the Airy Disk), that's is centered
and surrounded by a diffraction ring or two. Use a relatively bright
star to see this.

You can also use the Cheshire eyepiece with cross hairs that Orion
Telescope and Binocular sells. This way you can achieve collimation
anytime you wish, day or night. With the Cheshire you can align the
focuser to the objective's optical/mechancical center. The Orion
Cheshire would also work well with some other scope designs too. Its a
good tool.

Refractor collimation is probably more difficult to describe in words
than it is to do in practise.



Mark De Smet wrote in message ...
I've put togather a widefield refractor (62mm F4.5), but I am having
trouble verifying it's collimation.

Specifically, I can adjust the objective by several degrees, and cannot
see any difference in the performance. I have tried both a 26mm and 4mm
eyepiece (11 and 70 power respectively), I cannot tell the difference
between way off, and close collimation.

Any suggestions as to what I should see with an improperly collimated
refractor vs. a properly collimated one?

Is it perhaps that I am not at sufficient power to see the
imperfections? Or do I need to be in dark skies to see them?

Mark

"Mark De Smet" wrote in message
...

I've put togather a widefield refractor (62mm F4.5), but I am having
trouble verifying it's collimation.

Specifically, I can adjust the objective by several degrees, and cannot
see any difference in the performance. I have tried both a 26mm and 4mm
eyepiece (11 and 70 power respectively), I cannot tell the difference
between way off, and close collimation.

Mark,

Use a Cheshire, and everything should be fine. Take it outside on a nice,
sunny day. Put the lens cover on and insert the Cheshire directly into the
focuser and rotate is so the reflective portion is pointed toward the blue
sky. Look through the Cheshire and adjust the lens until all the
reflections you see are concentric. No need to worry further.

Clear skies, Alan

"Alan French" wrote in message
...
"Mark De Smet" wrote in message
...

I've put togather a widefield refractor (62mm F4.5), but I am having
trouble verifying it's collimation.

Specifically, I can adjust the objective by several degrees, and cannot
see any difference in the performance. I have tried both a 26mm and 4mm
eyepiece (11 and 70 power respectively), I cannot tell the difference
between way off, and close collimation.

Mark,

Use a Cheshire, and everything should be fine. Take it outside on a nice,
sunny day. Put the lens cover on and insert the Cheshire directly into
the
focuser and rotate is so the reflective portion is pointed toward the blue
sky. Look through the Cheshire and adjust the lens until all the
reflections you see are concentric. No need to worry further.

Clear skies, Alan


And please, please, please do not point it at the sun on this sunny day!
even for a moment! Hard boiled eyes are not attractive, and there is the
chance that the heat will melt cements, or other parts of the telescope.

Harvey