6/16/2010. And now
for something completely different. I've been using a Lumicon 1.5A prominence
filter for many years, and this week took steps toward improved sungazing.
The image above was made using a webcam a couple of hours after mounting
the Lunt LS60THa (that's shorthand for Lunt, 60mm, tilt-tune, hydrogen-alpha)
on a Giro alt-az mount. While I was hypnotized by the detail presented
by narrow-bandwidth sungazing, the fact is that I'm a photographer and
I felt positively evangelical about the intricate detail I was seeing
in the eyepiece: I had to show this to people! The usual afternoon
thunderstorm arrived just as I got the webcam working well but before
I could try it with the double-stacked etalons for "surface"
imaging.
Here are some Day 1 impressions.
As everyone else says about Lunt's 60mm hardware:
damn that's heavy, well-built gear! Amen.
The 6mm blocking filter (the aperture through which the
eyepiece sees what the objective delivers) is indeed a little claustrophobic
when it comes to finding the Sun (the alternative is a 12mm or 18mm version
which is more expensive and was not in stock from the vendor I selected).
The smaller blocking filter matters not at all after the Sun is found.
With a 20mm Plossl, the field of view feels very restricted (it is!),
but with the 7mm Nagler, you'd never know you were looking through a
keyhole: the view could not be improved with a bigger blocking filter
but the telescope would be more convenient to use when not equatorially
mounted and driven (center the Sun in the 6mm filter with this 500mm
focal length and the edge of the Sun will reach the edge of the filter
in less than a minute). The 7mm Nagler seems beautifully matched: the
magnification and field of view combine to minimize the "keyhole"
aspect of the small blocking filter while showing tremendous detail across
a wide apparent field of view. I have modified the foam in the storage
/ transportation case to allow it to remain attached.
With a single etalon (said to yield a 0.75A image), prominences
are bright and sharp. Detail on the disk is elusive: it's there but focus
has to be perfect, and you have to be ready to appreciate low-contrast
features. Think of planetary observing writ large. Tune the etalon, adjust
focus, look closely. Voila, disk detail is present, but it's well shy
of "arresting." The sky was clear much of the early afternoon,
but its color was a little milky. October's deep blue sky may show me
another thing or two.
With the second etalon in place (said to yield a 0.55A
or narrower image), the Sun's surface is considerably dimmer. But what
is revealed is beyond "detailed."
The face of the Sun becomes intricate, complex beyond words, with light
and dark structures flowing along magnetic field lines in patterns as
graceful and sweeping as the best-delineated spiral galaxies in big dobs.
The entire surface of the Sun is stippled with bright and dark detail.
The detail is as overwhelming as trying to enumerate the stars in a globular
cluster. The image is dim, but so what: the sight is breathtaking. This
view is up there in the top ten of my sky-gazing hits (M3 in the University
of Virginia's 26-inch Clark refractor; 3rd contact over the Sahara; the
1967 fireball; the 1984 "annular" eclipse; nightfall on Mount
Whittington; the Veil Nebula from Chaco Canyon in the 5-inch at F4.5
with O-III filter; my first look at the Trio in Leo...). Some kind of
cloak or hood would be helpful since the exercise is similar to what
19th century photographers faced: viewing a dim image in very bright
sunlight. Aluminized mylar or white nylon with a dark lining? Absent
sartorial splendor, a black garbage bag works well enough.
When viewed through a single etalon, the largest visible
prominence stood out brightly, with many striations, and appeared to
be pasted above the solar limb. It became three-dimensional when viewed
through stacked filters. That part which extends beyond the limb is seen
to be a continuation of a dark curtain silhouetted against the disk.
Just as plain as that. Bright stria in the projecting portion of the
prominence were matched by sooty veils in the projected bits.
Some longer filaments and bright patches around a pair
of active regions were the highlight of the afternoon's viewing. I hope
they don't turn out to be the highlight of the next year's solar observing,
but it seems entirely possible. That's how beautiful and striking the
view was today.
Here's a dimension that's hard to come by on the web:
the Lunt 60mm OTA is 90mm 89mm in diameter. Losmandy 125mm rings
work fine, and as a bonus, the shadows of the collimation bolts work
well as a Sun-finder. When using the clamshell, there is no similar natural
aiming device, but a Televue Sol Searcher would be inexpensive to buy
and something functional would be easy to cobble. We'll see about the
Losmandy 3.5-inch rings enroute from eBay; now that I've measured the
tube, I doubt they'll be useful for this instrument. They may work well
on the ST80 guidescope, though, so the 125's will be freed up for the
Lunt. I've modified a spare, short D-plate to attach to the clamshell,
and that might be the routine method of attaching the Lunt to the Giro,
the A-P, and for piggybacking it on the 5-inch refractor.
One more thing from the first day: if you have fasionably
sparse hair, try not to sunburn your scalp.
Here's a single frame grabbed from the Vesta Pro, before
stacking, before adornment:
