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Thread: Questions about focal reducer and filters/t-adapter...

  1. #11
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    Default Re: Questions about focal reducer and filters/t-adapter...



    Thanks everyone who has responded, it helps me a lot.


    Quote Originally Posted by OttoMann View Post
    Oh..
    Can you show me which one you use?
    Camera Adapters & T-Rings | Orion Telescopes: Shop

    The deal is the distance to the camera sensor needs to be 55mm. The image train I posted before is perfect for that. I am
    un familiar with the Orion adapter you use..
    It's this one:



    Also, what is the explanation behind it needing to be 55mm? Can you elaborate on that?

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    Default Re: Questions about focal reducer and filters/t-adapter...

    That's meant for a refractor ashelyy, get the reducer and the Celestron universal t adapter and call it good. That Orion is adding a lot of vignette.

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    Default Re: Questions about focal reducer and filters/t-adapter...

    Quote Originally Posted by OttoMann View Post
    The deal is the distance to the camera sensor needs to be 55mm.
    Are you sure that you aren't quoting the requirements for a Coma Corrector or Field Flattener ?? They often have 55mm Focal Plane requirements.

    SCT Focal Reducers do not otherwise most folks with a DSLR would be unable to use them - remember that the T-Ring spec calls for 44-45mm from the outer face of the T-Ring to the Focal Plane - leaving only 10mm for your stipulated 55mm distance of which even your suggested "#93633-A t-adapter" is longer than...
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    Default Re: Questions about focal reducer and filters/t-adapter...

    Quote Originally Posted by kegmont View Post
    That's meant for a refractor ashelyy, get the reducer and the Celestron universal t adapter and call it good. That Orion is adding a lot of vignette.
    Actually, given that the C6 SCT has only a 27mm Exit Baffle size, it wouldn't be the 1.25in Adapter (Orion or Celestron) that produces the bulk of the Vignetting...
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    Default Re: Questions about focal reducer and filters/t-adapter...

    Your saying the focal point is inside the exit baffle? then you'd be getting vignette at the eye piece

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    Default Re: Questions about focal reducer and filters/t-adapter...

    Quote Originally Posted by seigell View Post
    Are you sure that you aren't quoting the requirements for a Coma Corrector or Field Flattener ?? They often have 55mm Focal Plane requirements.

    SCT Focal Reducers do not otherwise most folks with a DSLR would be unable to use them - remember that the T-Ring spec calls for 44-45mm from the outer face of the T-Ring to the Focal Plane - leaving only 10mm for your stipulated 55mm distance of which even your suggested "#93633-A t-adapter" is longer than...
    The fact of the matter is through trial and error I learned
    Scope+focal reducer + 93633-A t-adapter+ tring + camera..... gives you the correct distance
    Phil Leigh and others confirmed this.

    But a 1.25 filter will not work in this configuration.
    Kurt

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    Default Re: Questions about focal reducer and filters/t-adapter...

    Thanks, so if I understand correctly, the longer the t-adapter is the more vignetting I'll get, and I would be better with a shorter one than the one I currently have?

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    Default Re: Questions about focal reducer and filters/t-adapter...

    Quote Originally Posted by ashleyy View Post
    Thanks, so if I understand correctly, the longer the t-adapter is the more vignetting I'll get, and I would be better with a shorter one than the one I currently have?
    No. Length has very little to do with Vignetting - in this case.

    It is the restriction of the smallest Inside Diameter element between your Scope and your Camera.

    As you are using 1.25in components, their inside diameters will be somewhat less than that - probably as narrow as 1.1in...

    However, the Exit Baffle (the "inside diameter") of your C6 Scope is also only about 1.1in (27mm per Celestron) - so there is rather little extra Vignetting being introduced by the rest of your 1.25in rig.

    Now, in general, "Length" of an Optical Train does have a potential to impact the Vignetting recorded at the Camera Sensor. This is because the Light coming from the Scope basically forms a Cone, with it's Base at the last Lens or Mirror and the Tip at the Camera Sensor. So, any restriction in the Optical Train is going to first impact that Cone if it is Closer to the Lens.

    But, the Light Cone in an SCT is rather "flat" - the Secondary Mirror is usually a very slow F/12-F/15 - compared to "faster" Refractors and Newts...
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    Default Re: Questions about focal reducer and filters/t-adapter...

    The Celestron focal reducer for the 8se is terrible, im not how it holds against the 6 but it also really depends how picky you are with AP.

    Check out my other post and the link inside which compares reducers and flatteners... nobody replied and that surprises me.

    TeleVue 0.8X Reducer/Flattener on a 8SE/C8 Scope?

    LINK to Comparison

    Someone else might be able to speak about the difference that you might get from a C8 vs a C6 scope and those reducers
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    Default Re: Questions about focal reducer and filters/t-adapter...

    Ok, so I actually got the focal reducer, and I tested it out with my existing T-Adapter... I can confirm that with the incorrect T-Adapter, it does have a fair bit of vignetting, but I was able to correct it—just not without some effort. Here's a sample of what I was able to achieve with the focal reducer:




    However, I actually just ordered a new AVX mount (which comes with a 6" Newtonian f/5 scope with 750mm of focal length) so I'm figuring now that I have that, maybe there's no reason to even have the focal reducer? I suppose could reduce the new scope, which would make it insanely fast at f/3.2, which would be nice, but I'm not sure if I would ever really need that. I'm considering returning it, but something tells me I should just keep it to have that option.
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