More Beginner's Questions

[Noidea]

Hi Again, all my questions were answered in my first tread, thank you to all. I would like to ask a couple more questions.

1. Can someone please explain Collimation to me? How and why it needs to be done?

2. I am wondering how the image in a sighting scope is upside down? I understand that in a reflecting scope it's because of the mirror but how can an upside down image be achieved in such a small thin inline scope?

Paul
:confuse2:

[mickoking]

G,day paul



Finderscopes have inverted images because that is the image a simple refractor makes. To make the image the correct way requires an extra lens which is not important in astronomy, the extra lens would add cost to the finder and rob it of some precious light ( the more lens elements you have the dimmer the image becomes). However you can get correct way round finders but you get used to normal finders soon enough. :thumbsup:

[vindictive666]

gday

do a search of the forums and you will fiond answers on collimation :)

[Noidea]

Thank you for that explaination. I am not concerned by the inverted image, it's ok with me. I was just interested to know how it works.

[Noidea]

Will do, thanks.

[davidpretorius]

Two I like to suggest using for a newtonian ie dob

The first one is very good to get the mechanical side of collimation going ie using a screwdriver to align the smaller secondary mirror near the top and then adjusting the bigger primary.

Take your time with the first link and do during the day.

This will get you to a stage of lets say 90% collimated and will do you for now.......fast forward a few months, you want your stars to focus pin point, your are imaging at high magnification and you want the image to be crystal clear etc etc ie you are getting a perfectionist!!!

This is when you star to get into the second article. It is about star testing. I hve been into the hobby 7 months and still am trying to perfect this seconf method.

So here they are

Easy starter: http://www.schlatter.org/Dad/Astronomy/collimate.htm

Fine tuning: http://www.schlatter.org/Dad/Astronomy/collimate.htm

Good luck and please ask lots of questions

[iceman]

Same link Davo

[xrekcor]

Dec 2005 AS&T has a great article on collinating telescopes.

or this is a pretty good article...

http://skyandtelescope.com/printable/howto/scopes/article_790.asp

if your going to learn you might as well learn the whole process. It looks
more difficult than it appears. And after a couple of goes at it you'll
soon get the gist of whats going on.

regards,CS

[janoskiss]

The Sky & Telescope article on collimation is pretty good: http://skyandtelescope.com/printable/howto/scopes/article_790.asp
(it's also linked on the page Dave P linked and Rob linked it too. It's a popular choice :))

As far as the inverted image is concerned it's very easy to understand once one gets the hang of the basics of ray tracing for ideal lenses and mirrors, which is nothing more than a few simple rules:

- incident parallel rays meet at a single point in the focal plane, and vice versa
- for convex lenses this occurs on the opposite side of the lens, for concave the same side, as the incident rays are on
- any ray passing through the centre of a lens will maintain a straight line course
- focussing mirrors work exactly the same way, except for the "flip" about the mirror plane (it is easier when ray tracing to just replace all mirrors with equivalent lenses (or nothing if its a flat mirror) to keep the diagram neatly flowing)

And that's about it. That's enough to get you an A+ in year 12 geometric optics, because everything else can be worked out from these simple rules :) (which I admit though need to be better explained and demonstrated than I've done here).

It's well worth investing a bit of time going through an introductory optics textbook, and getting to know the basics of ray tracing, because it lets one understand how a telescope and all the various eyepieces and other bits/attachments go together and work together.

[RAJAH235]

This isn't bad either >http://www.andysshotglass.com/Collimating.html
:D L.

[davidpretorius]

http://legault.club.fr/collim.html

sorry the star test one is this one!