A Challenge to the Quarkers out there – – –

To quote Holmes: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth”

I have been musing over my recent post concerning the apparent lack of fine detail on my solar images (https://roslistonastronomy.uk/h-alpha-question-puzzle). While they are comparable with other LS35 images I have seen, and with GONG images, they do lack the fine detail you sometimes see in other published images. I am not 100% convinced it isn’t a stacking artifact, but setting this aside what else could it be?

Daytime observing suffers from atmospheric turbulence big-time, and you need a fast shutter speed to reduce this. I wonder if I simply have not got the sensitivity to employ an appropriately fast speed.

Simple optics would inform me that a Quark with an 80mm scope has the potential of being at least 2 stops faster than my LS35, everything else being equal.

So, the challenge to the Quarkers – I know that there are at least 3 of you out there, and one of them at least (mentioning no names, Andy), has a Mikrokular, the same as I use:

Can you get finer detail than I get using a fast shutter speed? Simple stacking is likely not to help, as the images you stack will be slightly displaced due to the turbulence, thus blurring the final stack.



4 Responses

  1. Hi Roger

    The Daystar QUARK is a 4.2x Barlow type lens married with a 21mm h-alpha filter, with an integrated 12mm blocking filter.
    Here the settings I was using for the disc shot in http://roslistonastronomy.uk/first-light-for-new-solar-setup. The camera is a Celestron Nextimage 5 clone that I paid about £35 for.

    USB2.0 YW500 Camera]
    Colour Space=MJPG
    Output Format=AVI files (*.avi)
    Frame Rate Limit=Maximum
    Timestamp Frames=Off
    White Balance=4500(Auto)
    Backlight Compensation=0
    Apply Flat=None
    Subtract Dark=None
    Display Brightness=1
    Display Contrast=1
    Display Gamma=1

    One thing I have noticed is that JPG photos seem to lose loads of definition compared to TIFFS

  2. For what it is worth, here are the camera settings as reported by “Sharpcap” on the last set of solar posts I did.

    Prominence exposure:

    Frame Divisor=1
    Colour Space=MJPG
    Backlight Compensation=0

    Disc exposure:

    Frame Divisor=1
    Colour Space=MJPG
    Backlight Compensation=0

    I don’t believe these exposures! I don’t know what the speed means with web-cam type electronics.
    I normally do the disc using “auto” mode.
    For the prominences, I let the image drift to one side of the frame in “auto” mode. The exposure then increases and when I am satisfied with it, I press the “auto” button, that then freezes the exposure, and then re-centre the image.

    The Lunt is 400mm focal length, giving f/11.4
    With a X3 barlow that goes to f/34.2

    When imaging with barlows and a short scope focal length, you can’t trust the nominal magnification. This depends on all sorts of optical dimensions. The X3 was determined experimentally using a nominally X5 barlow.

    The Lunt has an external etalon mounted in front of the objective lens and is tilt-tuned. Etalon filtering works best for parallel light rays, so I would expect the higher the focal ratio the better.

  3. I was being a bit economical with my typing – -!

    After you account for various barlows etc but it should have said

    “Simple optics would inform me that for the same image size on the chip a Quark with an 80mm scope has the potential of being at least 2 stops faster than my LS35”

    That, I think, is true.

    Not sure about the speeds. Also not sure that Sharpcap reports them correctly.

  4. Roger, when Andy comes round again we’ll have to try out your theory…

    But>>>>> “Simple optics would inform me that a Quark with an 80mm scope has the potential of being at least 2 stops faster than my LS35”

    I’m not sure that is correct. The extra aperture offers increased resolution for sure over 35mm. But the Quark runs optimally at f/27-32, so much slower than the Lunt which I presume is around f/7-8. The eye would compensate for that difference but not a camera, which I believe would ‘see’ the dimmer view of a Quark at that focal ratio.

    What shutter speeds are you getting/using to help aid a future comparison – could you post your usual settings for surface capture and that of prominences…


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