When the cap and Hotech disagree

[Bigwings]

My 10" DOB (f4.7) gave me stunning views of the Orion nebula on a night last week of good seeing. 

Today I decided to check the collimation

The Hotech Lazer collimator showed it to be a fraction off so a little tweak was given.....then I popped the collimation cap on and it looked a bit off.....which is right?

Star test when I get to see some on Saturday.

Wonder what a big frac would cost.....only joking.

Clear skies

[alan potts]

If used correctly I would believe the Hotech, I have a deluxe Cheshire but I feel the Hotech is the one I trust on my M/N 190mm and 18 inch Dob. My SC and Mak I do only by defocused star, they don't need much attention but the Dob requires collimation every time of course as I biuld it.

[alacant]

Hi. I think either will get you close (if you're observing only, close enough?) but only the star test will nail it dead centre. You could always use an artificial star and so save time under the stars for when it clears.

To answer your question, if I had to go with one, I'd go with a Cheshire collimation cap. If you can get one with cross-hairs, you could do both secondary and primary. I find in the latter case there is very little difference if any, between it and the star test.

HTH

[Jason D]

18 hours ago, Bigwings said:

.then I popped the collimation cap on and it looked a bit off.....which is right?

Can you clarify what looked a bit off? Was it the collimation cap pupil reflection with respect to the primary mirror center spot? Was it the secondary mirror placement under the focuser?

You might the following post (and the one below it) helpful:

Jason