To See or Not To See

Discussion and instructions for astronomy-related projects
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Apollo XX
MSSF Coordinator
Posts: 2741
Joined: Sun Jul 11, 2010 8:11 pm

To See or Not To See

Unread post by Apollo XX »

Greetings Fellow ASSNE Members,

We've all been there (well most of us anyway). We've traveled to a nice dark observing site, brought all the important gear to see really dim things that are really far way, played by the rules and shut off all the white lights - and still, no faint fuzzy in the eyepiece!

Lights Too Bright.jpg
Lights Too Bright.jpg (1.7 MiB) Viewed 2424 times
Many of the so-called astronomy-friendly red lights available to astronomy enthusiasts these days are none too dark-adaptation friendly. In fact most of them significantly hinder complete adaptation. Light pollution is becoming a bigger and bigger problem with the recent proliferation of LED's and the observing field is no exception.

Could the problem lie in your choice of red light use in the field? In all likelihood, the answer is yes. The red lights that many of us use when navigating our charts and accessory changes are WAY too bright to facilitate proper dark adaptation of our eyes, and there are not a lot of good options available in the astronomy marketplace to help you address that.

The attached document addresses this issue and shows you how to construct good red flashlights for a pittance in funds that will help enable you to get the most out of your deep-sky observing sessions. I hope you find it useful.

Keep Looking Up!

Mike M.
"The purpose of life is the investigation of the Sun, the Moon, and the heavens." - Anaxagoras
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Paul D
Equipment Manager
Posts: 2108
Joined: Fri Mar 19, 2004 2:13 pm

Re: To See or Not To See

Unread post by Paul D »


I will go one better and say the imagers on the field using computers and cell phones are worse than the red lights. The red lights are usually only turned on for an instant while looking at a map or star chart and then turned off. The imaging computers and cell phones run constantly all night long. Regardless of mini tents or red screen covers there is still way too much light bleed.

Now I have done some experimentation on this matter, and this is what I found. Use of an amber colored light is ideal. Finding one is very tricky and amber LEDS are few and far between. Using a red light, the issue is not necessarily the light itself, more the light being reflected off a white page. Even the brightest of red lights used on a black atlas with white stars is very dim. Yes, dark adaptation is lost when using a red light on a white page because of the spread of light. (Notice your own image where all the red lights are pointing to the center of the page but yet the whole page is glowing red.) But the dark adaptation returns much more quickly than looking at a computer screen or cell phone. Red lights do not dilate the eye as much as other sources of light unless they are shined directly into a person's face.

Just my own observations and test.

16" f/5 Night Sky Truss (Midnight Mistress)
10" f/5 Home built Dob with Parks mirror.
Pre-Meade PST
Celestron Skymaster Binos 25-125x80
Meade Travelview Binos 10x50

See that 16" in the sleek black dress? She is all mine. :)
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