Different collimation for f/5 and lower newt?
- StarLord101
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Different collimation for f/5 and lower newt?
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Re: Different collimation for f/5 and lower newt?
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Re: Different collimation for f/5 and lower newt?
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Re: Different collimation for f/5 and lower newt?
Sometimes the secondary will seem to be offset more so if a spherical mirror but nothing to worry about.
Read the Astro Baby Collimation Guide, honestly the last place I go for good advice is youtube...
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Re: Different collimation for f/5 and lower newt?
As show in the image below fig b. , when one is using a centered secondary part of the light cone misses the secondary due to the angle of the fast primary and in general cutting across downwards on a triangle actually slices through a thicker portion while cutting on an angle away slices through a thiner portion,
Fig a is the correct mirror offset and fig c is somewhat doable that you can actually collimate a fast scope with a centered secondary but you would need to tilt the focuser after to avoid of axis tilt.
In addition you will find that visual scopes will have a smaller secondary as full illumination isn't as much in favour visual over imaging and that less obstruction is more ideal which gives you better contrast while viewing and also that the focal point is alot shorter for eyepieces so the fold of the light cone can be made higher towards the apex.
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Re: Different collimation for f/5 and lower newt?
When I did my first collimation with a short focal length F6 telescope this "centered" misinformation gave me a lot of headache! The important thing that the "experts" and collimation manual should say is : No collimated reflector does appear completely "centred" then looking down a Cheshire Collimating Eyepiece.....it is just more apparent when this is done with a fast reflector.StarLord101 wrote: ↑Thu Jun 04, 2020 9:18 pm I picked up an avx mount with the six inch celestron Newtonian reflector. I've done collimation before but it's been years, so I read some guides watched some videos for a refresher. Came across a few mentions that fast news f/5 and lower, you actually don't have everything all centered when it's properly collimated. I see a few examples that show what looks to me like a very non collimated state with some things centered and others offset. My issue is that with collimation, you have this target. It's correct when everything is round and centered. With that caveat though, I have no idea how to tell what my target is since I'm not necessarily trying to get something in a center mark. I could not find any clarification other than an aside like " oh by the way, fast will look more like this"
Here is a example of collimator instructions :
Here is a example of A perfectly aligned Newtonian telescope with focal ratio about 1.75. Displaying centered and
non-centered features: The reason is that the oval shape secondary mirror is "distorted" by 45 degrees so that it appears to be round when looking down the focuser tube. The centre of the image is not the centre of the mirror when looking at it at a zero degrees.
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