Dark comparison, sort of...

  1. KathyNS
    KathyNS
    Here are two darks, one taken with the JTW, with its temperature stabilized at minimum value, and the other for comparison taken with a 350D. Both are ISO 400, 60 seconds. Processed in PixInsight. Processing consist of identical Histogram stretches on both frames. Obviously, there is a colour balance issue and perhaps a sensitivity issue. I may need help from someone more knowledgeable about doing this kind of comparison. It looks to me like we are comparing apples and oranges.

    JTW dark frame:


    350D dark frame:
  2. whiteLion
    something is wrong.....what are doing oranges here?
  3. dp297
    dp297
    There are no color issues with darks.
    I would suggest to use ISO 800 or 1600. Nobody uses ISO 400 for imaging. And use perhaps 5min or 10min subexposures. If u have the time, it would be nice to see 10 consecutive 5 or 10 min subs in order to get the sensor hot enough.
    Now, for stretching by Pixinsight, just adjust the Histogram Transformation parameters (Shadows, Midtones and Highlights to the same values).
  4. KathyNS
    KathyNS
    On the contrary, ISO 400 is the recommended setting. Higher ISOs are only needed if you plan to import the image into 8-bit software that doesn't have the dynamic range to resolve a lot of different dark values. I do all my imaging at 400. The histogram transform is fine. I applied the same transformation to both darks.
  5. dp297
    dp297
    Keith if you look at many reviews by Honis, Stark and several posts in Cloudy nights u will see that the recommended settings for 350d and 550d is 800 and 1600. The darks should be at the same Iso. There is no reason whatsoever to use low iso since u are increasing your exposure time needlessly. This is called unity gain.
    I fail to understand why the Jtw dark is orange. It should be dark!
  6. ChuckWalters
    ChuckWalters
    On an unrelated email I received from Mark about my power supply shipment, he included the following statement in his email......I did not solicit this information! But I did think it was timely....take note of the ISO he lists.

    I got confirmation of shipping of the spare parts I ordered, they should arrive tomorrow, so you will be up and running. Hopefully you will not be looking at a clear sky now and cursing me. It is cloudy here… Looking forward to hearing your experiences, even if it’s cloudy get used to the camera. Make some dark frames, experiment with the ISO (6400 is best IMHO), get used to making the flats using TV mode. Etc. J
  7. KathyNS
    KathyNS
    Increasing the ISO simply amplifiess the signal (and noise, of course) after the image is captured. You can do exactly the same thing, with more control, in software. The ISO doesn't change what the sensor sees. On a 5-minute exposure, the sensor captures exactly the same number of photons whether the ISO is 100 or 6400. Cranking up the ISO just affects how the image looks. But how it looks is the job of post-processing, not of the camera.
  8. Phil Leigh
    Phil Leigh
    I ONLY use ISO 400. This is NOT causing you any kind of problem!!!
  9. Phil Leigh
    Phil Leigh
    THe JTW statement on ISO makes no sense at all. High ISO = high noise. Boosting the ISO is a POST SENSOR amplification so it can only boost noise as well as signal equally. Boosting signal alone is only possible by using longer exposures. Increasing SNR by stacking is only relevant if you have enough basic signal in the subs to get well away from the noise floor in the first place and ISO plays no part in that, only exposure time does.

    I don't listen to gurus, I go by actual results and my actual results are that ISO 400 (or below)is the cleanest for me on the following cameras:
    450D, 7D, 550D.

    Of course you do need to use proper 16-bit software such as PixInsight to process the data correctly...

    YMMV
  10. Phil Leigh
    Phil Leigh
    ... And as Keith said, stretching in post-production is always going to be cleaner than any combination of analogue and digital amplification applied in camera by boosting the ISO...
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