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Thread: The no-cost 10-step checklist for a better image

  1. #11
    Phil Leigh's Avatar
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    Quote Originally Posted by tedrampart View Post
    sorry to post to this again when no one has replied since my last post.. but I'm wondering about the 160 multiples and if those that only have 100 multiples (like ISO 100,200,400,800)... would it be the same basic idea to just do a +-EV to accomplish the same task? which could be done on camera or in processing?
    Sorry Ted - I thought your "Googling" had answered your own question about the 160 multiples?

    My understanding is that the in-camera method used to create the 160/125 multiples cannot be replicated exactly inside or outside of the camera using +/-EV adjustments.

    This is because the EV compensation alters exposure or aperture, NOT ISO... (except in "auto ISO" mode...?)
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  3. #12
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    Quote Originally Posted by Phil Leigh View Post
    Sorry Ted - I thought your "Googling" had answered your own question about the 160 multiples?

    My understanding is that the in-camera method used to create the 160/125 multiples cannot be replicated exactly inside or outside of the camera using +/-EV adjustments.

    This is because the EV compensation alters exposure or aperture, NOT ISO... (except in "auto ISO" mode...?)
    okay, I read in some forum someone saying it would accomplish the same basic task.. but what you're saying makes more sense.

    I'm hoping this firmware hack actually works the same way the pro cameras get 160 multiples. I couldn't find exactly how they accomplished this, but I didn't dig into the code for it. I'll have to see tonight if it stays clear.
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  5. #13
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    Default Re: The no-cost 10-step checklist for a better image

    Here are a few others...

    #???. Don't use an AC-to-DC transformer, or a DC-to-AC inverter, unless absolutely necessary. These can induce a very slight 60hz ripple voltage that adds noise to the camera electronics. It can also add tracking errors in some mounts.

    #???. Add a ground wire to your telescope setup when running on 100% battery power. I have a heavy copper wire attached to my aluminum tripod, which is attached to a long copper spike that I drive in the ground under my telescope. I also connect it to the negative side of my battery before I plug in my equipment (which all runs from the same 12v truck battery). This provides a solid 0v reference to the electronics and grounds out any RF energy the equipment might pick up. Think about it, long unshielded electrical leads, long aluminum or steel tripod legs, all act as antennas for whatever RF signals (or magnetic fields) are around. Grounding your equipment can significantly reduce the electrical noise introduced into your electronics by outside sources (especially nearby power lines). One thing, though. Make sure all of your powered equipment uses a negative ground on the chassis side (usually has a positive tip on the 12v connector).

    #???. Put rubber pads under your tripod feet to reduce vibration. You can also use black rubber pipe insulation (held on with tight zip ties) around the aluminum legs to reduce unwanted tripod harmonics.

    #???. Reduce unwanted light from entering your tube assembly any way you can. Light shields (dew tubes) work great, and can be made out of almost any lightweight tubing (I just started using a piece of 8" diameter cardboard concrete slip-form). Just line the inside with black rubber 1/16" hobby foam or flat black construction paper. In addition, put something between your scope and any nearby light sources. I often park my wife's Dodge Durango nearby, then throw a sheet of black plastic over it. This allows her to stay in the truck and read with the dome light on, but doesn't bother me even though I am only a few yards away.

    #???. Be quiet when the shutter is open!! Loud noise, especially low-frequency bass, can reverberate down your optical tubes just like organ pipes.

    Regards,

    Rodger
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  7. #14
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    Default Re: The no-cost 10-step checklist for a better image

    I have a couple of questions.

    (#4) What is binning and how do you do it one a DSLR. I always thought that was something done on a CCD, so I never paid much attention to it.

    (also #4) What is deconvolution?

    (#9) Do most of you dither between subs? Astronomy Magazine just had a short article on it, but the author suggested only shooting up to 16 frames and not using darks or flats. In his article he made some strong claims about the quality of dithered, stacked subs. I usually program my scope to take a series of subs and then do something else while the camera does it's thing. I didn't think about manually taking the subs so I could dither in between.
    Rob
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    Default Re: The no-cost 10-step checklist for a better image

    I don't dither between frames because I prefer not to touch the scope any more than I have to. The worst case is that a few hot pixels are missed in processing, but I can check for those manually using the dark frames. When dark frames are stacked up, the hot pixels light up fairly quick. A bunch of stacked darks should never have any bright pixels, so they are fairly easy to spot then mask out.
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  10. #16
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    Default Re: The no-cost 10-step checklist for a better image

    I do dither and I can only say that it makes a different.
    And I would also like to know how to perform binning on a DSLR. Did not know you can do that
    Gusztav


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    Default Re: The no-cost 10-step checklist for a better image

    I always dither... BYE interacts with PHD and does it for me automatically.

    As for in-camera "binning"... This is not relevant to DSLRs except for some video modes on high-end large sensor models.
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  13. #18
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    Default Re: The no-cost 10-step checklist for a better image

    Not all CCD pixels are made equal. Dithering helps spreading the error of individual pixel response (such as bias) across your image, rather than concentrating them in the one end-result pixel. You should end up with a higher quality image. Letting the image drift a little and then start imaging again is a form of dithering, but can lead to a 'streaky' type of background noise. The best way of dithering is to spiral outwards from the first frame.

    Hardware binning is great when you're trying to image faint subjects. While you won't benefit of reduced read noise, software binning can still make the difference between a usable and an unusable data set. With the huge sensors we have in our DSLRs these days, it is even often a good idea. This is because your scope or seeing conditions simply may not allow you to resolve a single pixel's worth of detail - in other words in those cases your data looks 'blurry' and detail is spread of multiple pixels.
    What you can do in those cases is two things; you can attempt to mathematically reverse the blur (deconvolution, which is only really useful if your signal is good), or you can decide to trade your excess in samples for a better signal until 1 pixel worth of data really corresponds to 1 pixel of detail.

    For example, binning to 25% resolution (averaging 4 pixels to make one new pixel) cuts your noise levels in half - this can make a huge difference!
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    Default Re: The no-cost 10-step checklist for a better image

    Great thread. Much food for thought and implementation. Thanks.
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    Default Re: The no-cost 10-step checklist for a better image

    good thread
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