Friday 25 November 2016

Preparing for very large sketch works - LMC sketch, pt 1

I have recently been commissioned to do a sketch of a very particular object, the Large Magellanic Cloud.  Both an honour to be commissioned by a professional astronomer for this piece, and also terrifying by the very nature of the beast I’ve been asked to chase down.

Every now and then, I find that a particular object I am considering to sketch, some preparation needs to be made.  Some of these preparations come from previous experiences and how they relate to my style of sketching.  As an example of one aspect of my sketching style is how I don’t use a “field of view circle”, or as I affectionately call it “The circle of Death”.  I tend to develop the scale of an object pretty much on the fly, letting the natural action of my wrist and fingers begin the scaling process and the rest takes care of itself.  And to this, an A4 sheet of paper is usually plenty big enough.

There are a few objects however that I recognise as being so large that an A4 sheet wouldn’t be sufficient to accommodate them.  For these I sought out an A3 pad of black paper in order to sketch them.  The Orion Nebula is one example where I deliberately used this larger sheet size.  As too the sketch of the Andromeda Galaxy.

This last one however brought to my mind that there are even some objects that even A3 is not big enough.  For me, the finished sketch of M31 is a little more “constricted” than I would have preferred.  If I had started the sketch with a slightly tighter wrist, and made the initial brush strokes tighter, then the final sketch would have been less constricted.  But the difficulty is anticipating the ultimate amount of expansiveness that M31 is to reveal.  So for the Andromeda Galaxy, I feel I still did pretty good, despite my own critique.

Now, the LMC is a different beast altogether.

While M31 has a maximum angular dimension of some 3°, the largest dimension angular dimension of the LMC is some 10.5°!  Flaming enormous!  Knowing my own style of sketching, I can see that even with an A3 sheet I would struggle to fit the LMC.

So, I need to build a larger easel to accommodate a larger sheet as the one I currently have can take an A3 sheet and no larger.

It is also not just a simple matter of scaling up what I currently have.  I also need to consider the experiences that I’ve had with sketching in the night air, and work out some ways in which to counter some of the problems that can be encountered.

One thing that is seen through the eyepiece during an extended examination of an object is the apparent rotation of the object in the field of view as the objects transits through the sky.  So to work with this is to rotate the sheet.

Another difficulty that can arise comes from dew.  While the shielding that the Coreflute wrap that I have over my current easel works very well most nights, it is those occasional nights of excessive humidity that overwhelms the shielding and the paper warps as it absorbs excessive moisture, and the texture of the paper is also altered to the point that it becomes soggy and impossible to continue working on without causing damage to sketch that’s been laid down.

Even how to illuminate the large sheet needs consideration.

So, time to work on Sketch Easel Mk II

I decided to utilize the same clamp mechanism to hold on to the sheet.  It is simple and effective, and with a little thought it can be made to allow for a broad rotation range of the sheet.  To help control any possible flapping from gusts of wind, I devised a few clips made from wire that I bent into shape.  These clips gently hold the paper down and their long reach allows them easily reach the paper even when it is tilted for rotation purposes.

While the shielding I’ve made has more overhang than the first Easel, if the night happens to be a humid one, particularly with the longer amount of time that this piece will take me, I’ve had to come up with some system by which to help control dew soaking into the paper.

I’ve long thought of different way that this could be achieved.  Heating the paper is one way, but the power requirements of such a heater is large and complex to design and fabricate.

I then thought about the way we control dew with our scopes – with the movement of air.  Dew does not form on a surface that has a constant stream of air flowing over it.  So I came up with a battery of fans to blow gently down the face of the page.  I’ve used two fans rated at 12V, installed in series so to reduce the airflow to a gentle blow, and not have the easel become airbourne.

Of course, this dew mitigation method for paper is purely experimental, though not without pedigree.   Time will tell how effective it is.

The lighting aspect I’ve addressed by having additional anchor points for the dual lamp that currently use.  I’ll also have some extra little reds lights in my pocket and tape in case I find I need some addition illumination.

Now that the Easel is done, I just need some eyepiece time with the Large Magellanic Cloud…



  1. Good luck with your project, Alex

  2. Alex, on the issue of dew formation it occurs to me the primary cause of the formation of dew is that the surface temperature of the paper falls below the dewpoint. This is largely a function of the radiant surface of the paper being exposed to the sky. Even in summer the radiant temperature of the sky will be shockingly low, often 70 Fahrenheit degrees below that of the ground or more. So one way to help with that would be to have some light, very reflective overhang to reflect some of the infrared being emitted by the ground back to the paper. Toward that end a foil-backed bubble insulation might be helpful. The link below is to an American example of the type of product. It ought to be moderately stiff over distances of half a meter or more in one layer

  3. Thanks Peter. It's going to be one of those that's going to suck my eyeballs out of my head!

    Hi Lee. Dew control in astronomy can be a vexed thing. Site selection is the best way of reducing it. That is why my preferred dark sky observing sites is up on ridge tops of mountains, and away from grassy lawns and agricultural land. Dew I've only experienced once up where I usually go two hours west of my home. But paper sometimes has a mind of its own...

    Warming the paper I have often thought about. Any method of powering up a heat source is difficult to implement, and then there is the issue of power supply in remote areas as heating is a major power drain.

    Your suggestion of reflecting heat up to the paper is innovative. I have seen similar products here in Australia too. Not a bad idea yours to utilize the overhang this way. I'll look into it.

    Your suggestion had me explore a little more the heating idea. It so happens that there are 12V heated pad for cars out there. These are thin, and some come with power regulators and not expensive. While still a power drain, it's not as much as my original ideas were about heating. A couple of car batteries would last the night for sure. Can be set up with a pulse mechanism so power is only intermittent instead of constant. Thanks for the kick along!

    I'll first give these fans a try. It cost me nothing to make this rig as I already had all the components. If it works, brilliant. If needs a reworking, I now have options.