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  1. #1
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    Default Is A 3.5mm eyepiece too much for my Celestron C8?



    Ok so I bought an Orion 3.5mm Stratus and tested it out on a mountaintop 1.5 miles away and I can't even get my C8 to focus the thing. I believe the eyepiece is just fine so that means that either my scope needs to be collimated or a 3.5mm is just to much magnification for the celestron C8. I suspect it is the latter.

    Anyone else use something this high powered with a C8 or similar scope?
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  2. #2
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    Quote Originally Posted by HeXploiT View Post
    Ok so I bought an Orion 3.5mm Stratus and tested it out on a mountaintop 1.5 miles away and I can't even get my C8 to focus the thing. I believe the eyepiece is just fine so that means that either my scope needs to be collimated or a 3.5mm is just to much magnification for the celestron C8. I suspect it is the latter.

    Anyone else use something this high powered with a C8 or similar scope?
    I would say that it within the 50x aperture limit of your scope but the limiting factor is most likely atmospheric turbulence. Those Stratuses are supposed to do with SCT's--but when seeing is poor due to atmospheric turbulence, all scopes have a hard time with higher magnification.


    But the lack of focus could be an focuser travel phenomenon--have you tried the eyepiece in both 1.25" and 2" mode--it can do either.
    Location: 30° 19' N; 97° 54' W; elev 248 meters; yellow/green zone; NELM 5.7
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  3. #3
    HeXploiT's Avatar
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    Quote Originally Posted by MarkM View Post
    I would say that it within the 50x aperture limit of your scope but the limiting factor is most likely atmospheric turbulence. Those Stratuses are supposed to do with SCT's--but when seeing is poor due to atmospheric turbulence, all scopes have a hard time with higher magnification.


    But the lack of focus could be an focuser travel phenomenon--have you tried the eyepiece in both 1.25" and 2" mode--it can do either.
    I don't even know what you mean by that statement. You mean connect it to a 2" adapter instead of the 1.25"?
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  4. #4
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    3.5 mm eyepiece plus a C8 SCT = blurry image

    Elementary HeXploiT, Elementary.


    The C8 is a 200mm f/10 telescope with a focal length of 2000mm. A 3.5mm eyepiece provides 571x

    Celestron advertises their newest C8s as having a highest useful magnification of 480x
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  5. #5
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    Quote Originally Posted by sxinias View Post
    3.5 mm eyepiece plus a C8 SCT = blurry image

    Elementary HeXploiT, Elementary.


    The C8 is a 200mm f/10 telescope with a focal length of 2000mm. A 3.5mm eyepiece provides 571x

    Celestron advertises their newest C8s as having a highest useful magnification of 480x
    Ok ok no need to be that way. I rather knew this to begin with but I wanted to try it for myself to SEE what too much was. I've learned over the years that if you automatically trust everything without trying it yourself you'll miss out on some things.
    In this case the worst case scenario is I turn around and sell the eyepiece for 10% more than it cost me.

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    Have an F/10 SCT C8 myself (specs sheet say its mirror is 203.2 mm in diameter with a 2,032 mm focal length) and I've never been able to use my 3.2mm TMB planetary on it because of too much magnification resulting in a blurry image. Maximum useful magnification really depends on the seeing conditions in one's observing site and the shortest focal length that I've successfully used on my C8 was one night with very good and steady atmosphere using a 7mm Meade Research Grade Ortho on Saturn, the planet looked really good and sharp - that's 290x. On the other hand, the Hyperion 8-24mm zoom allows me to dial in the right magnification of the moment given the stability of the atmosphere like when observing Mars earlier in the year during opposition, I can go from 10mm to 12mm or on very good night at 254x using the zoom's 8mm setting. One paramount consideration is the collimation of the scope - when I was very new to the hobby, I didn't know that my C8 was sorta off, and when I learned how to collimate, it really made a big difference - as acknowledged SCT guru Uncle Rod Mollise says, the difference is like day and night.

    Best,

    Hernando

  7. #7
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    I have a 4mm eyepiece that I use in my C8 WHEN I DO MY FINAL COLLIMATION TWEAKING.... so it actually serves a very useful purpose in my opinion...

    Bob G
    CPC1100 housed in a slotted domed observatory (Exploradome) 4 and 5 inch refractors for use from the lawn, a 8" Sct (NS 8i) for star parties...
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    Quote Originally Posted by HeXploiT View Post
    I don't even know what you mean by that statement. You mean connect it to a 2" adapter instead of the 1.25"?
    Before you pack up this EP for sale (if that is what you intend)--it may be useful to see how it can be used in either mode in case you get a similar dual function EP. I am guessing you have tried the EP in the 1.25" mode by sliding into your focuser with the 1.25" adapter in place. Now take the 1.25" adaptor out of the focuser and reinsert the EP and lock it down--it should fit fine--this is the 2" mode. Many folks actually prefer to use Stratus in this way because the center of gravity of this weighty EP isn't sticking out so far vs 1.25" mode.

    I forgot about the long focal length you have in this 8" instrument; 571x is too much power.
    Last edited by MarkM; 04-14-2010 at 01:45 PM.
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