Collimation

[PSALM19.1 (Shaun)]

Would collimating my Dob every time I use it be overkill? As in, would I wear out the threads? It's just so its perfectly lined up each time I suppose....

[Allan]

You should check your collimation every night you start out. Many times it won't need adjusting, but it's good to know everything's right. Many keen planetary observers re-check their collimation throughout the night, such is the importance of perfect collimation for planetary observing.

[PSALM19.1 (Shaun)]

Thanks mate

[doppler (Rick)]

My collimation is always pretty good and I only do one when I take the mirror out for a clean. If you do it right the first time and tighten the lock screws I can't see why anything should move?
My scope is a 40 y/o 200mm f6 newt so maybe the mirror (pyrex glass) and cell is made different than the newer designs?
But I would be interested in some explanations as to why collimation would change so frequently in some reflectors.

[AEAJR (Ed)]

If you check and everything looks good then there is no need to adjust anything. You are just confirming so nothing to wear out.

At first I was checking collimation about every other use but it was holding pretty well so now I check it maybe every 6-8 uses, about every other month. Mine lives in the garage on a cart and I roll it about 100 feet to the observing area, lift it gently off, then back on the cart and back into the garage. Rarely goes in the car and does not have to go through a cool down cycle, it is at ambient temperature. I have not had to adjust anything in months.

I would expect that if you travel a lot with the scope, bounce it around in the car, it is more likely to go out of adjustment. If it gets gentle treatment I presume it will hold.

I use a simple collimation cap for mine. I had checked it a few sessions back. One night I had friends over that evening. One has a Z8 and had his laser tool with him so he checked it. Said it was right on the money so that added a level of confidence that I am doing it correctly and that it is holding well. If you know someone who could check it after you think it is right that is another level of confidence you can achieve.

A simple eyepiece check is to put the scope on a bright star, centered in the eyepiece. I have heard around 10 mm as a good choice of eyepiece. Now, defocus the star. If it produces a concentric circle, even all around, you are well collimated. Nothing to adjust and you don't need any tools to do that. I do this every time I go out just as a spot check.

[raymo]

I'm with Rick on this one. I was ridiculed, and howled and booed off of this forum several years ago for saying that I rarely had to adjust the
collimation on my 10" dob. My present 8" Eq mounted Newt has nice
concentric star test, and I can't remember the last time I had to do a
tweak, and I do occasionally take it out in the car, and I have to take it off the mount after every session. I am very probably about to be
ridiculed again, but for normal every day visual use the collimation can be
quite a way off before the average user will see any observable effect.
Incidentally, I checked the collimation on my 1980s orange tube C8
when I bought it years ago, and have never had to adjust it since.
I understand that some types of scope are more sensitive to
miscollimation than others, and also some designs such as truss tube
scopes are usually going to need a tweak after assembly; I am primarily
talking about solid tube Newts, and, amazingly, the several SW collapsible
dobs I have owned or used.
raymo

[janoskiss (Steve H)]

I always check it but it rarely needs adjustment. But occasionally it does. If you have the locking screws in firm (you should be gradually tightening these, checking collimation as you go), your scope should hold collimation well for a long time.

But checking takes just a few 10s of seconds so it's good practice and you'll always know for sure. And in the unlikely case, when there is a problem, you will catch it early.

[barx1963 (Malcolm)]

The frequency of collimation checks is very dependant upon the type of scope. A solid tube newt is going to be more stable than a truss tube dob naturally. I always check my dob after assembly. As 90% of the time I am assembling in twilight or daylight, the couple of minutes needed is not taking away from observing time so why not check. It always needs a tweak but it is nice knowing that it is ready to go.
One of the first lessons I learnt with collimation was in relation to the locking screws found on many Newtonians. I always struck me as odd that we had an adjustment knob, a spring and a locking knob. If you tightened the locking knob, why was the spring there? And if felt like I had to do the primary collimation twice, once with the adjustment knobs and then again with the locking knobs.
Then at one of the early Snake Valley camps I attended, another user of the same scope advised my that the best thing to do with the locking knobs was remove them from the scope, walk down to the lake and pitch them as far into the water as possible. Al you need is adjustment knobs and good strong springs. To check the springs are strong enough t hold collimation, just move the scope to a variety of positions while checking.
Some scopes will have adequate springs, certainly the early GSO dobs had springs that were utterly inadequate.
The other thing to remember as far as primary mirror alignment is concerned is that the purpose of collimating the primary is to ensure that the coma free area of the image created by the scope is centred in the focuser (here I am assuming that the secondary and focuser have been setup correctly) and so get the best possible image. In a fast scope (<f5) the coma free area starts to get quite small so accurately centreing it is the way to go. Slower scopes have a larger coma free area so if it not precisely centred, the image will be OK as the stuff you are looking at is still within the coma free zone. That is why I regularly advise beginners who often have f6 or even f8 dobs and are getting stressed about collimation to relax and make sure they get it as close as they can and just go out and enjoy using their scopes.

Malcolm

[cosmo58]

i have a 5" starview eq 150 and does not have any collination screws or any sort of adjustment screws at all.it is just a straight piece of tube with australian geograhic on the side.but,however i always wanted to know what collimation was,the allignment of the primary and secondary mirrors.