Need Help in Collimating a Newtonian Telescope

boothee · Post by **boothee** » Sat Mar 29, 2008 9:40 pm

Hi!

I've been trying to collimate my friend's 8" Newtonian Telescope. Having some difficulties. Even both secondary and primary mirror aligned I still see the basement of the focuser misaligned. You can have a look in the attached picture.

I started from secondary mirror. Try to make it center, right below the focuser and adjust three screws to see the primary mirror.
Secondary mirror aligned nicely as follow:

Secondary Aligned?

Then, I move to primary mirror. Try to adjust primary mirror screws to be seen 4 spider arms equally in primary mirror. Looks like primary mirror also aligned nicely as follows:

Primary Aligned?

After all, I'm not happy as I couldn't see my eyes/camera lens right in the center.

I started again and again about 3 times. No improvement at all.
[smilie=crying3.gif]

Please help!

Thanks for your help and looking forward to your reply,

boothee

kayheem · Post by **kayheem** » Sat Mar 29, 2008 11:01 pm

Hmmm...I think you are seeing the effects of "secondary offset". Google this and you will find that this effect is seen when a scope is properly collimated.

Maybe other more experienced guys can contribute.

Post by **weixing** » Sun Mar 30, 2008 2:04 am

Hi,
That's the "secondary offset" after collimation. You can check the collimation using a star at high magnification.

Anyway, your method may not be that accurate for a fast scope. Should use at least a Cheshire/sight tube.

Have a nice day.

boothee · Post by **boothee** » Sun Mar 30, 2008 3:48 pm

Thank you for your kind replies. Now I have one more topic to read.

My friend is traveling to Kunming in early April. So I should ask him to get a sight tube for both of us. I hope he could find it there.

Regards,
boothee

rlow · Post by **rlow** » Sun Mar 30, 2008 4:12 pm

So I should ask him to get a sight tube for both of us.

You need a sight tube and chesire tube, separately or combined as one unit like the Celestron collimation eyepiece.

Alternatively, you can consider getting a well-aligned laser collimator, which is more convenient to use. One of the better laser collimator is from Howie Glatter, who provides great service. My collimator is off-alignment and he willingly service it free-of-charge to 15 arc second accuracy.

boothee · Post by **boothee** » Mon Mar 31, 2008 3:29 pm

rlow wrote:
So I should ask him to get a sight tube for both of us.
You need a sight tube and chesire tube, separately or combined as one unit like the Celestron collimation eyepiece.

Alternatively, you can consider getting a well-aligned laser collimator, which is more convenient to use. One of the better laser collimator is from Howie Glatter, who provides great service. My collimator is off-alignment and he willingly service it free-of-charge to 15 arc second accuracy.

Thanks for your suggestion.

For this time, I have to ask my another friend and use his laser collimator.

Clear Skies!

boothee

Post by **weixing** » Mon Mar 31, 2008 8:02 pm

Hi,
You need to center spot your primary mirror to use a laser collimator.

Have a nice day.

boothee · Post by **boothee** » Mon Mar 31, 2008 8:12 pm

weixing wrote:Hi,
You need to center spot your primary mirror to use a laser collimator.
Have a nice day.

Oh! Yes! I've cleaned and put it back. I forgot that!
Owner has made a center spot with white ink

. I have to clean it and make a new circle with sticker.

Thanks,

boothee