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Equipment Discussions >> Reflectors

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Dennis_S253
Pooh-Bah


Reged: 11/22/11

Loc: West Central Florida
inner and outer focus different
      #5554746 - 12/04/12 10:12 PM

I try reading proceedures but I don't find the answers I'm looking for. If my inner focus looks really good and then I start going to focus things start looking bad and as I go to outer focus I'm way off, what does that mean?

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dave brock
professor emeritus


Reged: 06/06/08

Loc: Hamilton, New Zealand
Re: inner and outer focus different new [Re: Dennis_S253]
      #5554952 - 12/05/12 12:59 AM

We need a more detailed description of exactly how the inner and outer focus images look.

Dave


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Dennis_S253
Pooh-Bah


Reged: 11/22/11

Loc: West Central Florida
Re: inner and outer focus different new [Re: dave brock]
      #5555348 - 12/05/12 09:33 AM

OK, I'll try.
When in outer focus, perfect donut, diffactions rings look picture perfect. As I start going toward focus I start seeing spikes to one side. Then when going to inner focus, I no longer have a perfect donut. If I make adjustments to make the donut perfect, then when I go to focus I start seeing spiking and as I go to outer focus it's not a donut again. It's like I'm chasing my own tail.


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: inner and outer focus different new [Re: Dennis_S253]
      #5555421 - 12/05/12 10:25 AM

Quote:

OK, I'll try.
When in outer focus, perfect donut, diffactions rings look picture perfect. As I start going toward focus I start seeing spikes to one side. Then when going to inner focus, I no longer have a perfect donut. If I make adjustments to make the donut perfect, then when I go to focus I start seeing spiking and as I go to outer focus it's not a donut again. It's like I'm chasing my own tail.




The Celestron 150HD is what Celestron calls a "Hybrid Newtonianin." These use a fast primary mirror, probably spherical, and a corrector to increase the effective focal length. However, unlike the typical Short Tube/Jones-Bird, I believe the corrector is mounted to the primary mirror side of the secondary mirror so that it sits between the secondary mirror and the primary mirror. Adjusting the tilt of the secondary also adjusts the tilt of the corrrector.

Collimating these scopes is somewhat different than collimating a standard Newtonian...

Jon


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Dennis_S253
Pooh-Bah


Reged: 11/22/11

Loc: West Central Florida
Re: inner and outer focus different new [Re: Jon Isaacs]
      #5555485 - 12/05/12 11:04 AM

Yes, I would agree Jon. Does anyone know where instructions can be found for this scope?

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