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Thread: if you have a 6 inch reflector , then buy an 8 inch dobsonian ..how many times

  1. #11
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    Does that matter with the type of scope? I currently have a 4.5" Newtonian and want to get a 6" catadioptric. The difference is $450 between the 6" and the 8". Any recommendations? I should mention that I don't like dobs.

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    Default Re: if you have a 6 inch reflector , then buy an 8 inch dobsonian ..how many times

    Catadiopic telescopes (like an SCT, RCT etc.) will generally have a longer focal length than a newtonian. I'm speaking generally here. Here's some specifics:

    Celestron C8 has 203.2mm aperture and a focal ratio of f/10. Which gives it a focal length of 2032mm.
    Celestron C6 has 150mm aperture and a focal ratio of f/10. Which gives a focal length of 1500mm.

    Celestron 114mm (4.5") telescope with a focal ratio of f/7.89 has a focal length of 900mm.
    Celestron 114mm (4.5") telescope with a focal ratio of f/8.77 has a focal length of 1000mm.

    In order to accurately compare telescopes you have to know 3 things:
    OTA design (Refractor [Apochromatic or Achromatic], newtonian [astrograph, bird-jones etc.], SCT, RCT...)
    Aperture
    Focal Ratio (from which using the aperture you can determine Focal Length, or knowing Focal Length you can determine focal ratio).

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    Ok. For example the C6-A-XLT versus the C8-A-XLT.

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    Default Re: if you have a 6 inch reflector , then buy an 8 inch dobsonian ..how many times

    Quote Originally Posted by gus1911 View Post
    I can tell you from experience that jumping from a 6" to an 8" is hardly worth the trouble - not much difference. Jumping from 6" to 10" is big. From 8" to 10" is not a big deal either, but moving from 8 to 12 is big. This can go on forever, as you might imagine. You need at least 2 jumps in size (6 to 10, 8 to 12, 10 to 14 etc) to make a difference. The limiting factors are portability, weight, setup time, and of course, $$. Always $$
    Don't quite agree here, personally I think it's not about sizes as such but more about percentage of area increase.
    The jump from 6" to 8" is exactly the same as going from 12" to 16" this is a noticeable jump. Many make exactly this jump and notice a good improvement.
    Personally I find the jump from 6" to 8" very worthwhile on DSO the 8" is clearly able to go deeper. It will reveal quite a lot more detail in objects like globs too.
    Obviously holding out and getting a 10" or a 12" would be even more of a WOW! Factor though
    Steve

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    Default Re: if you have a 6 inch reflector , then buy an 8 inch dobsonian ..how many times

    Magnification isn't a factor. With the proper eyepieces, a 6-inch can produce any magnification the 8-inch can. The difference is light gathering power. The 8-inch mirror collects more light, almost twice as much as the 6, and images are brighter...that's what is important. ;-)
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    Sorry but I'm fairly new to this, I guess I meant what would be the difference between getting an 8" OTA dob and putting it on my existing GEM over an 8" catadioptric. I've read about coma correctors and what not. Just wanted to get personal experience recommendations.

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    Default Re: if you have a 6 inch reflector , then buy an 8 inch dobsonian ..how many times

    You will need a really big mount to properly hold a 8" dob OTA. If you want to go with an equatorial mount, I think you are stuck with a catadioptric.

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    Default Re: if you have a 6 inch reflector , then buy an 8 inch dobsonian ..how many times

    This thread is nearly three years old. No doubt, the original poster has already made his scope decision long ago.

    Thread closed.

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