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  1. #11
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    If you shoot from standard tripod you probably can not go over 15 seconds... unless you shoot with really short lens (<50mm) Some say you can do 20+ sec.
    Make a few test shot and you will know. If stars look like tiny eggs, you need shorter time. Use remote control!

    Crank up your ISO to 1600, take max 10-15 second shots and stack those. I am sure your result will be better and you get less distortion.
    If you use camera lens, make sure its is not fully open, close it one or two stops (f).

    When you select images for stacking, exclude all shots with defects. If you have to exclude 50%-75%, do not worry.
    10 good shots is better than 20 shots of mixed quality (at least this is my conclusion after few tests)

    If you have some free time and tools, build a "barn door tracker" and you can use longer exposure.

    Cheers!

  2. #12
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    Ok, so with your setup, over the hour it takes to get the lights, you are experiencing significant field rotation. This is what's causing the edge stars to look swirly while the central ones are more or less OK. This is likely also what's causing your difficulty with registration and stacking.

    Field rotation is a problem with all alt-az mounting situations, and your photo tripod is essentially an alt-az mount. Some software procedures like "drizzle" can correct for a certain amount of field rotation. This is different from star trailing; field rotation occurs "between" your frames, over the length of the total exposure, while star trailing due to tracking error is within the single subframes.

    You can build a simple "Barn Door" equatorial manual tracking mount for about ten bucks or so; it will take a bit of practice to make it and use it but you will be amazed at how much better your photos will look. This will take care of your field rotation problem as well as star trailing during exposure.
    Barndoor Mount

    If you put your lights, along with twenty darks and twenty flats, into a .zip file and post it somewhere, I'll download it and take a look later on this evening.

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    ETX125AT guiding WO Megrez 90 Apo/CGEM mount w/ polar scope
    WO Multiple Reticle Red Dot finder, Celestron SkyMaster 8x56 binos
    26mm SP, 12.4 mm SP, 8.8 mm UWA, 12 mm MA illuminated reticle, 2x Barlow, 3.5mm and 31mm Hyperions, TV 2008
    Meade DSI Pro II monochrome CCD; Meade LPI; Celestron NexImage; Canon EOS RebelXTi
    EQ-1 mount (emergency use only!)

  3. #13
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    Here are the files I have http://www.gentryoffroad.com/iris/1stIRIS.zip (607mb)
    I am trying drizzle in iris but the first try didn't seem to do anything


    Basically I want to take pictures like these but have the stars look like what I processed in iris minus the rotation. These will be taken while backpacking so guiding and even a laptop are not practical due to weight and space. Is there any way to get better results than what I have below?




  4. #14
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    Those are nice shots!
    OK, what you are trying to do is technically called HDR or high dynamic range photography, where you have very bright or very dark areas that you still want to show detail in, while also preserving the more average illuminated areas as well.
    There is lots of stuff you can do in processing for HDR and there are specialized packages of software that will help. But you may find that you are going to wind up compositing several shots together to get the final result you want.
    The first thing is going to be getting the mount situation straightened out. You can only do so much in software to correct field rotation, it is a difficult problem and is best cured by arranging some kind of simple polar tracking mount like the Barn Door. Once you've got a decent stack of many frames of the sky image, then this can be combined with a properly-exposed foreground, maybe even just a single frame of the foreground, to make the full HDR image.
    I see no reason why you can't do the data gathering in the field completely manually using a remote shutter release button and a Barn Door. For the really widefield stuff you are doing, guiding isn't necessary if you can just get the polar tracking down and use short stacked exposures.

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    ETX125AT guiding WO Megrez 90 Apo/CGEM mount w/ polar scope
    WO Multiple Reticle Red Dot finder, Celestron SkyMaster 8x56 binos
    26mm SP, 12.4 mm SP, 8.8 mm UWA, 12 mm MA illuminated reticle, 2x Barlow, 3.5mm and 31mm Hyperions, TV 2008
    Meade DSI Pro II monochrome CCD; Meade LPI; Celestron NexImage; Canon EOS RebelXTi
    EQ-1 mount (emergency use only!)

  5. #15
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    Thanks for all the input, I think it is finally starting to sink in.
    I think this barn door mount will fit in my pack.

    The last one I saw a picture of was really bulky and made of plywood.
    Do you know if they sell a mount that acts like a barn door, is manual, cheap and more compact? Just the name of it would also work I can't seem to find it.

  6. #16
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    take a look at those.
    Some are good and some are pure overkill
    Building a Barn Door Tracker for Camera Astrophotography

    I like this one. It is simple and reduces tangent error. Just leave out the motor and drill some large holes to the board to reduce weight.

  7. #17
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    I downloaded and used Deep Sky Stacker.
    With the default settings i got pretty close to the same thing as IRIS produced. This was probably due me being a little too to figure out IRIS.

    On the second run I used the "Use Bayer Drizzzle algorithm (no interpolation, no debayerization). I also turned up the brightness on the raw files up to 8.0 because I shot them at ISO400 and DSS was having trouble picking up stars.

    Then I ran it threw Photoshop with auto level and auto curves this is the result.


    There is still some field rotation but not as bad. I am going to try and turn on the Drizzle x3 and play with the aligning options. I bumped my virtual memory up to 80,000MB so hopefully that will stop the out of memory error.

    I also came across a nice lightweight compact motorized (9V) barndoor.
    Barndoor


    It seems to take nice pictures too.

  8. The Following User Says Thank You to whokrz For This Useful Post:

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