why it is that you cant make a newtonian telescope that can be 'locked' in place after collimation is achieved. Why do newtonians require more adjustment than say, an SCT? Sorry if this is a dumb question
Smaller (<8") sonotube scopes should hold collimation extremely well requiring little or no readjustment after initial alignment. Assuming a good secondary holder is used and properly tensioned and that the primary is fixed in place with locking screws.
However large mirrors on pad floatation systems will move, and truss tube scopes can never be reassembled exactly the same way twice.
The small amount of time (less than 2 minutes with the right tools) required to collimate a large truss tube scope is a small price to pay for such excellent portability.
If the primary and secondary are well supported and well designed, there should be NO need to re-collimate. I've moved my scopes all around the world and never had to re-collimate.
Do newtonians need more collimation than SCT's, or do SCT owners in general just not bother?
As the others have said, a lot depends on the mechanical rigidity of the scope. My gso 10 incher only needs the finest of tweaks every now and then.
I certainly dont bother collimating every session, but I do check it occasionally.
Do newtonians need more collimation than SCT's, or do SCT owners in general just not bother?
I have a go at collimation with my SCT pretty much every night out but I'm on a bit of a collimation 'kick' at the moment. Don't know what other SCT users do, but I'd be interested to find out.
Hi Toc,
Firstly..it is not a dumb question..(if you never ask, you never know!)
Secondly...a collimation free Newtonian?..where the fun in that?..Seriously though..the design of most newtonian's allow for some movement in the optics for things like temperature variances, vibrations in transit, etc. I check my 10" dob prior to viewing and adjust when it needs it..after all...you travel all that way for a clear sky...fine tuning the optics is also worth the effort.
I have not had to collimate my LBvery much. I do mostly leave it assembled, it's only been apart twice so far for trips. I've marked the trusses to make sure I'm putting it back together the same way and it's never needed more then a slight tweak.
But I agree with some of the sentiment above, I actually enjoy collimating, it only takes a few minutes and you kind of build a relationship with your scope beyond sticking your eye up to it, which anyone can do..
The longer the focal ratio the less a reflector needs collomating. A well made F10 Newtonian may never need collomating after it's initial adjustment. I have a 300mm F5 Dob and I collomate it every time I use it. It only takes a few minutes and it guarentees the best possible image my telescope can deliver.
What effects focal length in your scope?
1. Temperature differences in the atmosphere (seeing)
2. Surface errors on the objective.
3. Errors on the secondary mirror.
4. Aberrations in the eyepiece.
5. Imperfections in your own eye.
6. Errors in collimation of the optical parts.
If each effected the on the incoming light ray in the same way and by the same amount the effects would be additive. We could tolerate a max of only 1/24 of a wavelength of sodium light in each (1/4 wave). We can do better, of course, and 2,3 & 6 can be kept to a minimum, but there is not much we can do about the others.
Errors that might not be obvious:
Wedging error in the mirror. If the mirror is thicker at the edge at one point than another there is more tilt to be made during collimation.
If the curve generated is off centre by a couple of millimetres then placing a central dot doesn't help as it is not "on-axis".
So we get it as close as possible and hope that all is well.
