Sky and Telescope - October 2016 - 6

Letters

I really enjoyed Alan Hirshfeld's "The
Nebula War" (S&T: June 2016, p. 36) and
the involvement of 19th-century amateur
astronomer Isaac Roberts. Although Roberts concentrated on astrophotography of
deep-sky objects, he is also known for his
photos of Neptune and for the ﬁrst-ever
photograph of an asteroid, 80 Sappho, in
December 1886.
Roberts mounted his photographic
plates at prime focus of his 20-inch reﬂector, to avoid the loss of light that would
occur from using a secondary mirror.
Moreover, his best deep-sky images were
taken from 1890 onward, after he moved
from Maghull, north of Liverpool, to his
Starﬁeld observatory on Crowborough
Hill near the southern coast of England.
His reﬂector ended up in London's Science Museum.
Philip Corneille
De Haan aan zee, Belgium

Debating Red vs. Amber Light
My congratulations to Robert Dick for
his very excellent article on night vision
(S&T: June 2016, p. 22). His explanations
are extremely clear and understandable.
My experience with color vision and
measurements comes from working for

TOM SALES

Mating a pill vial with a
small ﬂashlight can yield
amber-colored illumination
for use while observing.

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October 2016 sky & telescope

UNIVERSITY OF CAMBRIDGE

In Praise of Isaac Roberts

On the night of June 14, 1887, Isaac Roberts used his 20-inch reﬂector to take a 60-minute-long
exposure that captured the short trail of asteroid 80 Sappho (circled). He ﬁrst imaged it in 1886.

RCA on the development of color picture
tubes. This article has ﬁ lled in some gaps
in my understanding.
George Gadbois
Lancaster, Pennsylvania
I agree that the main problem with using
red light is that you can't see anything
with it! If it's true that an amber light
of just 1 or 2 lux will suﬃce for a nightvision-friendly ﬂashlight, then this represents a huge breakthrough for astronomers, especially amateurs.
I wanted to fashion an amber ﬂashlight for myself, so I tried to locate a 590nm LED. But I managed to jury-rig an
amber light by pairing a Garrity singleLED ﬂashlight with an old amber-colored
pill vial. (I knew they had to be good for
something!) I've tried it, and it works! It's
possibly a tad too bright, but if I don't
stare directly at the LED, it seems to leave
my night vision intact.
The best part is that it gives out a
gentle glow when placed face down, making it into a miniature amber lantern. I
accomplished that by lining the inside
with several layers of parchment paper to

diﬀ use the light sideways. The light is a
pretty color, reminiscent of candlelight,
and is easy to read charts by, even in "lantern" mode. Yet, when used as a ﬂashlight, the beam passes nicely through the
bottom of the vial, which then simply acts
as an amber ﬁlter.
Tom Sales
Somerset, New Jersey
Robert Dick responds: Thank you for taking
the time to explore this topic. One key aspect
of any luminaire is to eliminate glare. Glare
from a red LED will compromise your night
vision too. So the optics and shielding are
almost as important as the spectrum of the
light. Most ﬂashlights can't be dimmed very
well, and as you pointed out this is necessary. The peak in the spectrum is not too
critical, so what you are using is ﬁne. Minimizing (avoiding) blue is critical, however.
Upon reading "Is Red Light Really Best?"
in the June issue, I arrived at a conclusion
opposite to the author's - using the same
data. He makes it clear that studying a
star chart in faint light requires the high
resolution that only cone cells provide.

Sky and Telescope - October 2016

Table of Contents for the Digital Edition of Sky and Telescope - October 2016