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Thread: focusing a dslr

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    Default focusing a dslr



    I'm very new to AP, and thinking of buying a used C8-SGT to get my feet wet. I realize it's not the ideal AP solution, but I think it will work to get introduced to the hobby. It comes with a focal reducer, which from what I understand, that will help.

    I have the t-adapter for my canon cameras, and have tried using them in my 10" dob for moon shots. Well, I can't focus without unscrewing my barlow lens and inserting it on the bottom of the t-adapter. Will I have to do that with this C8-SGT schmidt cassegrain? Or will I be able to mount my camera and focus without the extra barlow glass in between?

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    Default Re: focusing a dslr

    Newtionan telescopes like your DOB often do not have sufficient back focus to focus a DSLR.

    The C8SGT has no difficulties with back focus. You can connect your camera directly to the telescope using a t ring and t ring adapter with no focus issues.

    A SCT has a focal ratio of f/10 which is on the slow side for photography. Many of us use a 0.63 focal reducer to lower the focal ratio to f/6.3. One aspect of a focal reducer is that it does reduce the back focus of a telescope; however, a SCT has sufficient back focus for a focal reducer ... even my small 4 inch SCT.
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    Default Re: focusing a dslr

    Thanks sxinias, much appreciated. This C8 does come with a focal reducer, so that's good.

    Now, although f/10 is a bit slow for ap, it just means longer exposures to get the same result, correct? Or does changing it to 6.3 improve other areas of ap as well?

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    Default Re: focusing a dslr

    Quote Originally Posted by MrDanner View Post
    Thanks sxinias, much appreciated. This C8 does come with a focal reducer, so that's good.

    Now, although f/10 is a bit slow for ap, it just means longer exposures to get the same result, correct? Or does changing it to 6.3 improve other areas of ap as well?
    It also means you get a larger AFOV which means you can fit larger objects - like Nebulae - onto the image.
    Plus, focussing is easier with more light and tracking is (slightly) less critical.

    Focal reducers are pretty much essential AP tools for DSO work on most scopes (except for dedicated fast astrographs)

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    Default Re: focusing a dslr

    I had to make a low-profile adapter for my scope. It gives me about an inch of focus travel. You might be able to buy one, I couldn't find one so I took a t-ring and an adapter, split them, and glued them together. It works fine.....that's the only problem with reflectors I've found so far....
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    Default Re: focusing a dslr

    I run a 10" F/10. It is nice to have a focal reducer although not always necessary. It really depends what you're trying to fit on your sensor. Also focal reducers will flatten your field.
    I also have that little glitch with my Celestron refractor. If I put the focal reducer on I don't have enough movement to focus. It's not a problem with SCTs though.
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    Default Re: focusing a dslr

    Yeah, I tested my SCT today with my canon and panasonic bodies and they all focused perfectly, with and without the focal reducer. Super excited for the clouds to clear and try this out.
    MLaferriere likes this.

 

 

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