Monday, 6 August 2018

Sunset at the Straight Wall reveals amazing detail

Hi all,

This is my second lunar sketch done using eyeglasses.  I’ve adapted a headband magnifier so it can carry a pair of spectacles suited to my eyes.  I’m getting used to the new way of sketching as there is now an additional step in my eyepiece-to-sketch-pad routine.  But the difference using these specs makes is well worth any initial discomfort.

I got up very early on Sunday morning for the chance to sketch something during the ¾ phase of the Moon.  As it turned out, seeing wasn’t the best despite the wee hour and cool temperature, but the occasional glimpses of remarkable clarity made the effort worthwhile all the same.

With all the lunar features on view tonight, it was an old favourite that most caught my attention, Rupes Recta, the Straight Wall.  I’ve sketch the Straight Wall during the ¼ phase as the Sun rose over this escarpment (see below), but this particular phase had the Sun setting, and the wall instead of being a dark shadow, was brilliant white, and the very low angle the sun was at cast the most remarkable long shadows and revealed a textured surface and details of this area of Mare Nubium that were jaw-dropping remarkable.

From the above sketch of the Straight Wall, the higher angle of the Sun leads one to think that the flooded ghost crater the Wall sits in is relatively smooth and not particularly textured.

Now, move the phase forward some 14 days, with the Sun casting its last rays across this same area at a glancing angle, and a staggering textured and tortured surface is revealed.  The Straight Wall and Rima Birt are not the only geological formations here.  Just west and running parallel to the Straight Wall is a long straight “depression” or fold that is roughly as long at the Straight Wall itself.  This long depression is crossed by Rima Birt, and continues on straight northward.

Rima Birt itself is remarkable in that its official selenologic origins are somewhat uncertain.  Most likely it is a rift fault that then allowed lava to erupt up along through the fault.  And as my sketch progressed, I picked up two volcanic domes (Birt 1 & 2) at the northern end of Rima Birt, the larger of the two sitting right on top of the rile!

The glancing angle of the fast setting sun also reveals so many other obscure features.  The oh-so-faint rims of several ghost craters are just barely visible – one being outlined by the chain of mountains, west of the Straight Wall, that circumvents and suggest the basin in which the Straight Wall sits in.  A highly pock-marked field of craterlets lies scattered south of Birt.  The faded ray system that extends southward belonging to Birt.  Several winding folds of old lava flows form wrinkles across the moonscape.  Long string-like streaks of light are cast eastward from the northern end of the Straight Wall across a jet black otherwise invisible plain.  And of course the curious twin peaks of dark shadows cast by the crater Birt across the brilliant white escarpment.

Object:  Sunset along the Straight Wall and surrounds.
Scope:  8” SCT
Gear:  10mm Pentax XW, 200X
Date:  5th August, 2018
Location:  Sydney, Australia
Media:   White and grey soft pastels, charcoal and white gel ink on A5 black paper

This was a remarkable session for me.   From starting not wanting to repeat a feature I had sketched before, a little time spent with it showed an astounding amount of invisible details revealed only by having the sun at as low an angle as possible before it dips below the horizon.   Quite superb!


Using Eyeglasses with Telescopes - one solution

Well, age has caught up with me.  I started to wear eyeglasses over the last couple of years as I’ve started to struggle with close up focusing.  This was fine with reading, but now I’m needing to use glasses with my sketching.  This has created a problem when I go to and fro between sketch pad and eyepiece and now needing to lift and replace the glasses from my nose.  This is a problem not just for those who sketch, but also for those people who make observing notes, and for microscope users too.

Lifting, holding and replacing traditional eyeglasses constantly is a fool’s game.  There had to be an easier way to make the switch.

I started looking into headband magnifiers.  Many of these come with an assortment of different lenses that provide different degrees of magnification.  I purchased a set that appeared to be light weight and as an added bonus has a pair of white LED lights built in.

My initial testing at home was most promising.  This headband set has a double articulating joint which allows or the lens to be lifted and for the whole LED assembly to be lifted too, and as the lens is attached to this element, the lens is able to clear the eyepiece safely.

The ultimate proof is using the headset at the scope while doing a sketch.  I used the headset on two occasions with the supplied lenses, once with a lunar sketch and the other with a DSO session.  As it turns out, the concept is good, but the supplied lenses are not.  The lenses are designed for close up work, and these lenses are not suitable for my purposes that has the sketch pad at a longer distance than these lenses work at.

Another problem with these lenses comes from the way they are made.  As the individual lenses are attached to each other with no spacing, the field of view when using these lenses is very narrow, and ultimately impractical.

My eyeglass script is mild, and at a pinch the ready-made glasses available at pharmacies  work well for me.  So, the thought occurred to me to swap the lenses that came with the headband for one of these inexpensive pharmacy eyeglasses.  If the experiment works, I can look at making a new set of lenses of my script.  By making use of these eyeglasses, I would also make the field of view much, much larger

So, I chopped up one of the supplied acrylic lenses to use the coupling mechanism it has, and attached it to the eyeglasses also using acrylic.  The arms on the eye glasses I cut off.  If I unscrewed the arms to remove the, it would have left two long tags would become a hindrance and get in the way when moving to and from the eyepiece.

Now for the third field test and proof of concept.  This was a lunar sketch.

The result was successful.  The new lenses are much easier to use, with no noticeable eye strain, and with a much larger field of view.  With this successful test, I can look at having a new eyeglass script made up for me that I can modify to fit this headband.  Of course, not having to use eyeglasses is easier, and I will need to get used to the actions of lifting and lowering the lens, but the gain of clarity of image is well worth whatever hassles using glasses presents.  I’ll post this latest lunar sketch in a separate blog entry.