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  1. #1
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    Default Problem shooting flats



    I have an Alnitak/Optec Flat-Man 7 5/8" and shot a series of flats recently on my 80mm Takahashi FSQ 106 scope with narrowband filters. I'm getting weird results. See attached showing 4 images as follows (left to right, top to bottom): luminance 1", OIII 10", H-a 60", SII 70". I thought maybe the dew shield was responsible for vignetting in two of them (I collapsed it as far as possible; it doesn't seem to be removable) but why not all of them? Likewise, two are sharp and two are fuzzy.

    I'm mystified why I am not getting full screen illumination on all of them. Does anyone have any ideas?

    Thanks.

    Geoff
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  2. #2
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    Default Re: Problem shooting flats

    What was the adu of the frames? What duration?

    They are very odd looking as though they are way underexposed or something.

    Might also want to try a T shirt flat or something and rule out the device you are using.

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  3. #3
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    Default Re: Problem shooting flats

    Thanks for your reply. I don't know what the exact adu is but the camera is an Atik 11000 with 10.7 mega pixels and a pixel array of 4007 x 2071. Likely not the problem, especially since the lights I want to calibrate are fine. The durations are indicated as 1, 10, 60 and 70 seconds. Sorry that was confusing. The Flat-Man is set at 100% intensity and is illuminated uniformly so I don't think the problem is there either.

    Yeah, that's why I'm stumped too!

  4. #4
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    Default Re: Problem shooting flats

    You should know what adu your flats are coming in at. 30,000 is pretty common but it varys from one camera to the other.

    I remember shooting flats for my ATIK 383L+ with narrow band filters and they were taking like 3-10 minutes using my home made flat box turned all the way up. When I shot rgb flats it was less than a minute and I had to turn the box down.

    Something about the badwidth of the led light really effecting the duration of the flats.

    My guess is that your under exposing the flats. You really need to find the proper exposure duration and the best way to do that is to look at the adu. Resolution and pixel size is irrelevant.

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  5. #5
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    Default Re: Problem shooting flats

    very strange, When you do flats are you keeping your scope focused at infinity? You should not have to drop or remove your dew shield, just place the flat-man perfectly flat across the dew shield. Does the flat-man look evenly illuminated when it is off the scope? Does your camera show vignetting with this scope when you take a picture of something during the day?
    John

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  6. #6
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    Default Re: Problem shooting flats

    Replying to Super Giant: first two questions are yes and yes. I’ll try the third. Good idea.

    To Ulterior Modem: by adu are you referring to the histogram output? At the exposures I’m using the pixel readout is already to the far right. I’m not sure I’m looking at the right graph though because the values max at around 1000 instead of around 65000.

  7. #7
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    Default Re: Problem shooting flats

    I discovered the cause of the first two images (top row). Light was leaking into the filter wheel through a USB port so I taped over it. Still looking for the cause of the bottom row.

 

 

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