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  1. #1
    Astronewb's Avatar
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    Default Can't focus with Barlow& Barlow.



    Hi, just a quick question. Was out for a while last night setting up a iOptron 90mm for imaging with a Bahtinov mask. I was unable to achieve focus using the Bahtinov. All I really got was a large star with no spikes? I removed the barlow (2x) and was able to focus perfectly without it. Focus stars were Polaris and Duhbe, same results with both Anybody esle have any difficulty with a Bahtinov and Barlow? And, is there a fix?

    Btw, the barlow used for visual works perfectly (Zhumell/GSO 2x ED).

    Paul
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  2. #2
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    Default

    I know with my barlow I have to add an extension tube to be able to focus it for imaging.
    Currently using a
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  3. #3
    Astronewb's Avatar
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    Default

    Quote Originally Posted by Scott F View Post
    I know with my barlow I have to add an extension tube to be able to focus it for imaging.
    Good point, but I'm able to reach focus with the barlow during the daylight hours, it just won't give me any 'focus spikes' using the barlow. Should have kept some images to post, but I deleted them.. Well, I'll keep playing with it to see what happens. Thanks.

    Paul
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  4. #4
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    Default

    Try sliding the Barlow back until either the Stars grows fatter or gets smaller and you reach focus. If it hits focus, use a guesstimate of the extension required to reach focus. From experience, Field Flatteners and Focal Reducers have extended th Light path, so I would expect that a Barlow would also extend the light path. AlanP

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  5. #5
    Astronewb's Avatar
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    Default

    Try sliding the Barlow back until either the Stars grows fatter or gets smaller and you reach focus. If it hits focus, use a guesstimate of the extension required to reach focus.
    Thanks Allen, that's one thing I didn't try. Next clear night I'll give it a shot, I have plenty of extensions/spacers.

    Paul
    Life's a journey, enjoy the ride
    OTA's: Borg 125SD, AR152mm, ES152mm Comet Hunter Orion xx14g , SVR90T-AP, AT6RC, AT10RC, Borg 60ED. Borg 50mm Achro
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