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Thread: Guidescope for SC8?

  1. #1
    Join Date
    May 2004
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    São José dos Campos, São Paulo, Brazil
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    254

    Guidescope for SC8?

    Hi,

    I have a Meade LXD75 SC-8AT f/10. I was told that I should get an autoguider for better deep space imageing, but I don't know how to choose a scope for it. I don't know which ones are compatible with my SC-8. Could you help me?
    English is not my first language.

  2. #2
    Join Date
    Dec 2006
    Posts
    3,275
    With moving mirror scopes use a off axis guider rather than a guide scope. It will save you a bunch of headaches.

    Rick

  3. #3
    Join Date
    May 2004
    Location
    São José dos Campos, São Paulo, Brazil
    Posts
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    Rick, is that because the focusing mechanism allows more flextures?

    Talking about SCT particularities, which kind of motorized focusers are indicated for it?
    English is not my first language.

  4. #4
    Join Date
    Dec 2006
    Posts
    3,275
    RoboFocus makes motorized a focuser that turn the focus knob on the scope. No separate focuser needed. Works well according to those I know who use it. Backlash isn't an issue as the unit always comes to focus from the same direction. Couple with FocusMax (free software) and you will have a perfect focus system.

    Flex comes from many sources. Meade claims to have removed the mirror flop in this scope but so far I've not seen any reports from users. Even if true there are other flex points with separate guide scopes. When I used one I had to support the scope with super rigid rings including the focuser and camera as even very expensive focusers had flex from the camera weight. Both imaging and guide focusers flexed, just differently. Once I gave up and went to off axis guiding all these issues vanished as both guider and imaging CCDs saw the exact same flex. It was still there but didn't matter. I know imagers who still use separate guide scopes but they are guiding short focal length scopes at 3" and greater resolution, not the much higher resolution of an SCT. Even then they end up throwing out a frame or two most nights due to flex issues. Then too due to this they are limited to 10 minute subs before flex starts to show up more often. I can run for 60 minutes with narrow band filters without an issue. I can work all night and not need to align my subs as those taken hours later are still dead on. Though usually if working with that many subs I'll dither the frames which then does require alignment. No way that would be possible with a separate guide scope. While expensive they do make image splitters that pass an IR image to a guide scope of the same field the imager is seeing at visual frequencies so you can guide on anything in the field. Handy for asteroids and comets. But you do need a guide scope that is sensitive to IR light, many aren't. I've not tried this but have a friend who swears by his unit. 50 years ago in film days a friend tried something similar (manual guiding back then) using a beam splitter that sent 10% of the light to the guiding eyepiece and 90% to the film. Didn't work well as at 10% he often didn't have enough light to see a guide star.

    Rick

  5. #5
    Join Date
    May 2004
    Location
    São José dos Campos, São Paulo, Brazil
    Posts
    254
    OK, an off-axis guider seems indeed more practical for me.
    English is not my first language.

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