noctilove
18
JAN
2015

A colourful conjunction

Comet lovejoy and the pleiadesComet Lovejoy continues to impress as it swiftly passes through the winter sky. A conjunction with the Pleiades and Hyades star clusters in Taurus set up a beautiful wide-angle photo opportunity last night for which I was lucky enough to have clear skies. The intensely green comet, the electric blue Pleiades and the vibrant orange of Aldebaran formed a colourful celestial triangle.

This is the first image I’ve taken using the excellent new softon filter which really makes the brighter stars in the constellations pop out, as well as emphasising their true colours. It should be especially good for wide-angle shots as a way of making the constellations more recognisable. As with all the filters I use, I bought the largest size possible, then simply use step-up rings to fit them to any of the lenses.

Image details: Nikon D7000Nikkor 50mm f1.8 at f4. 8 minutes (8 x 60 seconds) at iso 1600. Using didymium filter and softon filter. Stacked with Deep Sky Stacker and tracked with barn door tracker.

Comet Lovejoy imaged with Nikon D7000 at 180mm f2.8Despite painfully cold fingers, I persevered with the hand-driven barn door tracker to capture a few closer shots with the 180mm lens. The comet has certainly evolved over the few days since the last shoot.

Image details: Nikon D7000Nikkor 180mm f2.8 at f2.8. 5 minutes (5 x 60 seconds) at iso 1600. Using didymium filter. Stacked with Deep Sky Stacker and tracked with barn door tracker.

Comet Lovejoy stacked in DSS Using Deep Sky Stacker’s comet mode lets you fix the comet’s motion, revealing more detail in the structure of the tail.

Image details: Nikon D7000Nikkor 180mm f2.8 at f2.8. 10 minutes (10 x 60 seconds) at iso 800. Using didymium filter. Stacked with Deep Sky Stacker and tracked with barn door tracker.

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  1. Bill Krosney Reply

    Beautiful image of Lovejoy, the Hyades and Pleiades.

    Really, really, like the effect of the Softon filter. Enlarges the brighter stars and creates a more “natural” image and very visually appealing.

    Can you elaborate more about the specifics of the Softon filter you used? A Google search reveals Kenko produces a Pro-Softon A and B version. Also Hoya has both a “Softon” and a “Softener” filter. Interested in the specifics of the filter you’ve used.

    Thanks…

    … Bill

    • Nick Reply

      Hi Bill,

      Glad you like the effect – it really brings out the colour of the stars too.

      The filter is a Hoya Pro-1 Digital Softon-A, which gives a more subtle effect than the softon B filters, along with higher light transmission. I’ll aim to do a post/review of the filter in the next week or two.

      Nick

  2. Bill Reply

    Thanks Nick, I’ll certainly look to add that filter to my arsenal as well. Much appreciated.

  3. fco Reply

    Hi nick,

    Very beautiful shots especially this one. Very interested by your barn-door design, lends me to building a new manual one based on this “isoceles” design 🙂 — I already have a cam/controller-corrected motorized one but with vibration 🙁

    However a few things bother me (sorry to ask here, no comments possible on your barndoor guide page, no other contact info):

    – I calculated that 274.3mm with M8 rod assumes a thread step of 1.2mm;
    However references tell a M8 step of 1.25mm (a 4.2% difference); Since this is a bigger value it means that you must have spaced your beeps a small bit more than exactly 5s… is that the case ?

    – I calculated that with turning the handle every 5s, the pause between turns should incur a trail of approx. 75 arcsec, which should give about 13 pixels with 180mm lens and 16M DX sensor.
    The point is it should be very noticeable, but your shots are perfect; So the question is “what is the trick”, and how do you turn the handle ? Is it a turn-and-stop at every beep, like advertised on many sites, or do you turn continuously just using the beeps to synchronize the handle on the marks ?

    • Nick Reply

      Hi there – thanks for the comment, and glad you like the shots 🙂

      You’re right to query the figures as I haven’t included any calculations in the build guide. The guide I originally followed was for an imperial design, so converting it to metric could potentially have led to a few errors here and there. However once built, I manually calibrated the timing beeps to iron out any discrepancies with the calculations, or inaccuracies in the build itself, by adjusting the timing beeps by 1/25ths of a second until the tracking was spot on over several minutes. This has given a slightly longer beep gap of around 5.2 seconds, as you say.

      The guide site could do with a few updates as I have refined the design recently and added a few more enhancements, so I’ll also update the timings to read 5.2 seconds to avoid any confusion. If you fancy supplying the calculations/formulas you’ve used I’d be more than happy to add those to the site as it may help people make their own modifications.

      For turning the handle, I always use a continuous motion, especially when using the 180mm lens. For wider shots this probably isn’t necessary, but I think it also helps to stop any accidental knocks etc.

      • fco Reply

        Actually I’ve done the drawing and maths on paper, then wrote the maths as formulas in a spreadsheet. I will be glad to send you the sheet, if only you tell me the format you want to publish or examine (original format is GNumeric, I can easily make ODS or XLS), and an e-mail…

        As you already had several good ideas, now you told it, I’m very eager to see what enhancements you made 😉

        • Nick Reply

          That sounds great, many thanks – an XLS file would be perfect. I’m not sure what format I’ll display the formulas on the site, but the credits can go to you. My email address is nick[at]noctilove.co.uk

          One upgrade I added to the site today is using a laser pointer for polar alignment. This is not an original idea (and is sometimes frowned upon!) but it works extremely well. A second laser could also work for quickly targeting an object to photograph if mounted on the camera’s hotshoe. Other improvements I have lined up include a simplified, sturdier layout – but this part I still need to build!

  4. andreas Reply

    Hello
    My name is Andreas from Germany.
    I have a question for the barndoor tracker.
    Why did the length of 274mm threaded rods with M6.
    The correct length is 228,56mm.
    What is the advantage in 274mm.
    sorry for the English.

    • Nick Reply

      Hi Andreas,

      No problem – the advantage of the longer length is a larger margin for error when turning the handle, making the tracking more accurate.

      228mm is the correct length if the handle is turned once every 60 seconds. But for the M6 version I describe, the handle is turned more quickly (roughly once every 50 seconds).

      Hope that helps 🙂

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