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Thread: Flat frames always come out black.

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    Default Flat frames always come out black.



    Basically I've been trying to do my flat frames from what I see and read on the Internet and I keep getting the same result. My master flat frame always comes out way to dark almost black. I've always been doing them right before dusk and I've done them with a T-shirt over my objective and I've tried doing them with no T-shirt over the objective. I've even tried doing them inside using my laptop as a white screen. Can anybody give me any pointers on what I could be doing wrong? Should I try doing them when the sky is brighter with a T-Shirt over the objective?
    Scott
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    Default Re: Flat frames always come out black.

    Scott,

    are you sure they're black and it isn't the screen stretch? Unless you take them in the dark with no light, there's no way they could be black unless you forgot to remove the cap.

    Dan
    Dan Crowson - O'Fallon MO

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    Default Re: Flat frames always come out black.

    You shoud shoot your darks with the camera on aperture-priority automatic ("Av"). The camera will choose an appropriate shutter speed for the correct exposure. Unlike darks, which must be shot at the same exposure time as the lights, flats can be at a different exposure time. The result on automatic will be a medium gray, which is what you want.
    neal_mlc and stepping beyond like this.

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    Default Re: Flat frames always come out black.

    I have my camera set to AV mode. I did notice the ones I did yesterday, the individual frames came out a dark bluish color. I had a white t-shirt over the objective and the sun was just below the horizon. I'll try again another time when we have clear skies again
    Scott
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    Default Re: Flat frames always come out black.

    If your camera is in Av mode and the frame is coming out black, there is something wrong with your camera. Check to see if the exposure compensation (the +/- control) is set to zero. It should be. Maybe the camera batteries are low?

    If your camera's automatic exposure isn't working properly, you'll need to set the exposure manually. Do a series of frames, changing the exposure time on each one until you get a good exposure. If you check the histogram, the peak should be in the middle of the graph. Once you know the right exposure, shoot your flats.

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    Default Re: Flat frames always come out black.

    Keith to make sure I am doing this right, I should be taking flat frames right at dusk when the sun goes below the horizon and put a white t-shirt over the front of my scope?
    Scott
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    Default Re: Flat frames always come out black.

    Quote Originally Posted by jazzin View Post
    My master flat frame always comes out way to dark almost black.
    Are your individual flats black too? What does your histogram look like when you image the individual frames? What software are you using to capture them? And to stack them? How many flat subs are you using?

    Paul
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    Default Re: Flat frames always come out black.

    My individual flats are always a dark bluish color. Also I haven't quite yet figured out how to get the histogram graph to show on my Canon T1i
    Scott
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    Default Re: Flat frames always come out black.

    Quote Originally Posted by jazzin View Post
    My individual flats are always a dark bluish color. Also I haven't quite yet figured out how to get the histogram graph to show on my Canon T1i
    I'm not a Canon DSLR user but I believe most use software called BackyardEOS to capture images with Canon cameras. Hopefully that could help you.

    Try it out and see.

    Paul
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    Default Re: Flat frames always come out black.

    Could it be that I'm just not waiting till the sky is dark enough?
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    Scott
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