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In Over My Head?

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Posted by Steven A. Crosby on September 25, 2001 16:33:25 UTC

Thanks for the response.

Now that I think I'm beginning to understand what I'm doing (maybe), let me ask about something else that's bothering me about the light cone. I'm afraid the answer is going to be more in depth than my current level of understanding can handle, tho....

So where exactly is the focal plane in relation to the ocular? As I understand it, the "light cone" is really truncated because the "top" of it is a circular area lit to varying degrees by light arriving at the primary mirror. Where I get lost is as the light comes near the ocular. I would suspect that the lenses of the ocular will change the light path; it will no longer be a straight edged cone. I also assume it is the ocular's job to present the final image to the retina. So, where is the focal plane of the primary mirror - at the first lens element of the ocular, somewhere inside the ocular body, at the exit (pupil?) of the ocular, at the retina, or some other point I haven't mentioned?

How does the focal plane relate to "Spare Focuser In Travel" found in NEWT? I've been told to set that spec to about .5", but I don't understand why. Is there some measurement I need to do on my eyepieces to set this spec correctly?

I guess the bottom line is that I want to make sure that I will be able to get each of my oculars to properly focus, whether I use a 4mm or a 40mm ocular.

Thanks in advance for any help.

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