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    Question 8" SCT + GSO Crayford Focuser + TV 2x Barlow



    I'm considering purchasing a few upgrades for my Meade 2080 (8" SCT, f/10). I would like some feedback from the community. FYI, I am only interested in planetary imaging. My imaging camera is an ASI120MC and I'm using the stock mount with equatorial wedge.

    First and foremost, I'd like to upgrade my focuser. I find it very hard to achieve focus with the coarse knob. It requires the tiniest adjustments and since I'm using the stock fork mount, the view wobbles for a good 5 seconds after. Really makes imaging a pain. I would like to augment it with a GSO Crayford 2-speed focuser. I've heard good things about this and it fits within my price range. There also seem to be added benefits of 1) no image shifting 2) no mirror flop (though I haven't observed those effects yet) and 3) less wobble when adjusting focus since I'll have more delicate control.

    I also would like to update my 2x Celestron barlow (came as part of this kit) to a Televue 2X barlow. The Powermate is far outside what I'm willing to spend at this point and I've seen the barlow available used for reasonable prices.

    I welcome any and all advice/comments, but I have a few specific questions:

    1) From my research, the Crayford adds up to 378mm of focal length, bringing my total focal length to ~2400mm (f/11.8). Since I do planetary, this is fine with me. However, if I add the barlow in, that brings it up to f/23.6 (or more if the magnification is > 2.0). That puts me at 0.16 arcsec/pixel. I'm worried this might be too much focal length for nights of average seeing. Without the Crayford I'm at 0.19 arcsec/pixel.

    2) How much improvement should I expect to see going from the generic Celestron barlow to the Televue barlow?

    Thanks in advance everyone!

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    jaetea's Avatar
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    Default Re: 8" SCT + GSO Crayford Focuser + TV 2x Barlow

    Hi,

    First off, welcome to the forum. Glad you're here.

    Two things for you to consider:
    #1 Will focuser add so much onto the back end of the OTA that this gear will hit the mount when you try to slew to the zenith. My understanding is that the 8" SCT just doesn't have the clearance for this. If this is the case, consider the FeatherTouch Micro Focuser. It replaces your stock focuser. I have one they are great and well worth the money.

    #2 I routinely use my 2X barlow in my 11" f/10 SCT effectively giving me 5600mm of focal length. Remember that a night of average seeing is only average to the human eye. When you are taking 30-60 images per second what you are striving for are those very brief periods when the seeing is superb. So always go with as long a focal length as your mount will still provide smooth tracking.

    I use the Celestron 2X barlow imaging and don't know what extra value the TeleVue will give you.

    Cheers,
    JT
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