M31: up to 200mm

Experience with tackling M31 using the fixed tripod and the 50mm lens made me realise that these objects (let’s not forget M31 is one of the most accessible) need longer exposure and longer focal length lenses.

That means using the equatorial mount, and all the issues of polar alignment and motor drives that go with it.  The first kit upgrade is therefore a set of motor drives, one for each axis of the EQ3-2 mount.

200mm @ f/6.3, ISO 6400, 330 sec.11 x 30 sec. frames stacked in DSS.

200mm @ f/6.3, ISO 6400, 330 sec.
11 x 30 sec. frames stacked in DSS.

Polar alignment here was by eye (using the hole where the polar scope would go if I had one), followed by several phases of 2-minute drift alignment using the 500mm reflex lens.  The whole process takes just over half an hour.  This gives acceptable results with 30 seconds exposure at 200mm.

200mm f/6.3, ISO 200, 5 min.

200mm f/6.3, ISO 200, 5 min.
Single frame of 300 sec.

Made bold by success with 30 seconds, I push the capabilities of the new motor and my skill at aligning to try five minutes per exposure.

200mm f/6.3, ISO 200, 40 min. 8 x 300 sec. frames stacked in DSS.

200mm f/6.3, ISO 200, 40 min.
8 x 300 sec. frames stacked in DSS.

After a few tweaks in Photoshop, this stack of 8 frames of 5 minutes each looks pretty good.

4 thoughts on “M31: up to 200mm

  1. Dear Simon,
    Thank you for this nice webpage, and wonderful photos on it!
    I just bought my Skywatcher 130/650, and have a Nikon D60 with 18-105 and 55-200 lenses, almost just like you. I was very happy to find your Andromeda photos, using with my own equipment.
    I have some questions, if you would be so king to answer them. Unfortunately I couldn’t find any contact to you.
    Yours sincerely
    Andie (from Hungary)

      • Okay, thank you for the quick reply!
        (and first of all, sorry for my poor english, which is not my native lang)

        So, as I already told you, I have now almost the similar equipment, what you had years ago: A Skywatcher 130/650 (which is not coming in mind at this moment), and a nikon D60 with the 2 lens above.
        I tried to make a photo of the Andromeda some nights ago. I attached the nikon to the telescope’s back (piggyback), with the 18-105 on front of it. Zoomed to 105, and positioned to the M31. I made 20 shots with iso800, max aperture and 8 sec / shot. Made 20 darks and 20 bias after that.
        Loaded them in DSS, and tried to process, but the max I could get was a very noisy picture, with a 10×10 pixels fox in the center (that was the M31 for sure)
        I try to show you: http://kepfeltoltes.hu/141015/andro2_16_www.kepfeltoltes.hu_.jpg

        So, what did I wrong? How could I do it better, to get closer to your beautiful pictures? As far as I see, the first step is to buy a motor onto the Eq2 to drive it for 1-2 minutes shots – am I right?

  2. Hi Andie

    First, you don’t need to apologise for your English, it looks fine to me!

    It is very difficult to say what is wrong with a processed photo, but here are a few ideas and suggestions.

    Make sure you are stacking RAW files, not jpegs (Nikon RAW files have the suffix .NEF).

    Dark frames – yes, okay, but at the start, try stacking only the light frames and see whether this makes a difference.

    Bias frames – these are not needed if you are using dark frames. The dark frames also contain the bias information, so bias is eliminated by dark frame subtraction.

    If there is some vignetting, however, flat frames will help this.

    Try changing the settings in DSS. Start with the recommended or default settings and then make changes. I got very different results when I changed the “save” settings for the processed photo. The “autosave” was never satisfactory.

    My memory of DSS is that it was inconsistent and frustrating. Sometimes it worked well, but other times it just refused to cooperate. In the end, you will love it or hate it, but don’t give up! Keep trying different settings until you have learned what they all do.

    Let me know how it goes!

    A few more thoughts…

    Are you using your telescope “piggy back” instead of a fixed tripod? When I took my first image of M31 it was from a fixed tripod see here: https://simoninthelakes.wordpress.com/2012/09/18/m31-andromeda-first-attempt/

    For the fixed tripod, you need to remember “the 400 rule”. Divide 400 by the focal length of your lens, to find the maximum exposure length without star trailing. So for your 105mm lens, 400/105 = 4 seconds. With 8 seconds, the stars will trail. The next step is the motor for the RA drive of your EQ mount.

    At maximum aperture, there will be some distortion, so I always close down the lens a couple of stops to eliminate this.

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