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Is toooo bright red light affecting night seeing?

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#1 fdboucher

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Posted 30 March 2023 - 02:03 PM

My friend with 60 years' observing experience uses an expensive, miserable (…to me…) red light from a reputable astronomics provider to pore at his maps…

I prefer the red/white Coast HX4 flashlight I bought at Canadian Tire for 20 bucks. It provides a wider field of light projection and is significantly brighter, although I can not quote a measurement in lumens for the red light… it is rated at 80 lumens in white…

My friend tells me that even red light can ruin your night vision if it is too bright…

That is not my actual experience. While it does reduce my adaptation, the effect is minimal, short-lived and lasts for no more than 2 minutes…

Is there any actual data or biological plausibility suggesting that red light at a high luminous flux negatively affects night seeing?

Actually, green light is probably better for looking at maps without ruining one's night vision…

https://thehikingaut...r-night-vision/


Edited by fdboucher, 31 March 2023 - 09:59 AM.

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#2 Nemo51

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Posted 30 March 2023 - 02:08 PM

High flux, like a high colonic, varies from person to person….


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#3 norvegicus

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Posted 30 March 2023 - 02:09 PM

yes, brighter is worse at every wavelength


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#4 Astrojensen

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Posted 30 March 2023 - 02:13 PM

 

My friend tells me that even red light can ruin your night vision if it is too bright…

And your friend is absolutely correct. Even looking at the night sky with the naked eye affects your dark adaption, and you can reach significantly higher levels of dark adaption, if you keep your observing eye in total darkness, when looking away from the eyepiece. 

 

Basically, if your red light is bright enough for you to be able to read a map or write notes, it's bright enough to significantly affect your dark adaption...

 

NB! If you're observing from a light polluted site, you may never be able to reach levels of dark adaption that allows you to notice the impact a red light can have on dark adaption. 

 

 

Clear skies!

Thomas, Denmark


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#5 ButterFly

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Posted 30 March 2023 - 02:14 PM

Any light creates afterimages, which need time to clear.  Despite not necessarily triggering rods (depends on the red light's actual spectrum), the brain still sees afterimages.

 

For data relevant to you, collect your own.  Get good and dark adapted, unbleaching as much rhodopsin as you can.  That will take about half an hour to an hour.  Then clear your afterimages as best as you can.  That will take days, weeks, and months, to fully clear, but we usually only have a few hours.  Compare your views over several sessions (to average out seeing and transparency) at the one, two, three, and four hour marks.  Then, when you are comfortable knowing your own body, shine a red light directly into your face!  Use a red filter if you want, just to preserve your rod night vision.  Compare a view immediately before the offensive photo blast to right after.  If you used a red filter, you can be sure that your rhodopsin is still mostly unbleached.


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#6 ngc7319_20

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Posted 30 March 2023 - 02:15 PM

I guess my experience is that a bright enough red light will impact night vision.  Though the impact is generally minor.  Also, there is a wide range in what is marketed as "red" light.  Sometimes there is a small amount of blue light coming through "red filters".  Or the "red" is somewhat orangey and has some effect on night vision.


Edited by ngc7319_20, 30 March 2023 - 02:16 PM.

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#7 weis14

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Posted 30 March 2023 - 02:15 PM

My view is that under dark skies I want to use as dim of red light as possible.  I believe that bright red light matters, at least to my dark vision.  I also don't like to use LED screens without red filters due white to light leakage. 


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#8 Rustler46

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Posted 30 March 2023 - 02:36 PM

I was at the Golden State Star party a few years ago. One night I looked toward the west, and there was what looked like a railroad engine coming down the tracks towards me with a very bright red headlight. It turned out to be a newbie with a very bright red headlamp. Likely he had heard that what is needed was a red light to preserve night vision. So he got the brightest one he could find. There are many to choose from on the web. This certainly helped him see better as he was heading to his destination at the party. I tried to communicate with him about how inappropriate his light was. But it seemed like he didn't speak English.

 

So much for the "wisdom" found on the internet. As for reading star charts or seeing other things near your telescope, use the dimmest light that allows you to see. Use the deepest red you can find. Limit the amount of time your eye is exposed to light not coming from the eyepiece. Turn down the brightness on your electronic device. Employ night vision mode so that its color is toward the red end of the spectrum. 

 

We don't want to add any light pollution to what we must endure from external sources. My observing site at home is a "cocoon" protected from any direct view of local light pollution sources. I have neighbors on two sides that have very bright, white LED "security" lights. There are at least 3 street lights within one block of my home. All of these are blocked by vegetation or buildings from my observing position. It isn't perfect, but it helps a lot. If I need anymore light at all it is very dim and very red.

 

Russ


Edited by Rustler46, 30 March 2023 - 03:47 PM.

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#9 Jon Isaacs

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Posted 30 March 2023 - 02:39 PM

What I do:

 

I use a tablet running SkySafari Pro for my charts.  I use a deep red film screen to block the light leakage from the pixels in all colors but red.  

 

I have an app called Screendim Full that I use to a the screen.  I use my SQM to measure the brightness of the tablet's screen.  I adjust the screen brightness so it is at least 0.5 magnitudes darker than sky overhead.  

 

 The skies are generally darker than 21.0 mpsas and I shoot for 22.0mpsas on the tablet.  It's pretty dim but with my stronger than normal readers, I can see it quite well.

 

I need to remember to turn up the screen brightness when I am finished because if I don't, then I can't see anything and I have to go into a closet or dark room to see if it is on or not.

 

Protecting my night vision is my first priority.

 

Jon


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#10 fdboucher

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Posted 30 March 2023 - 02:39 PM

High flux, like a high colonic, varies from person to person….

lol.gif

This is hysterical…

Excellent point!

Actually, my own eyes will readapt very well in 1-3 minutes after looking at my (dimmed) computer screen… (after a first adaptation…).

This surprised me at first, because it DOES take me 20-30 minutes for the initial adaptation… ("SIRI: éteindre TOUT!").

But you are right: it is a very variable and personal experience.


Edited by fdboucher, 30 March 2023 - 02:45 PM.

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#11 fdboucher

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Posted 30 March 2023 - 02:40 PM

NB! If you're observing from a light polluted site, you may never be able to reach levels of dark adaption that allows you to notice the impact a red light can have on dark adaption. 

THAT is, sadly, very true…


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#12 Mark SW

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Posted 30 March 2023 - 02:45 PM

"What's the point about red light at the telescope?
At the telescope, we use red light for reading charts (at least we should!), to keep our photoreceptor cells dark adapted. This is true only for our rod cells, as the red-sensitive L cones will be activated by red light (and should be, as we want to read our charts). In order to impair rod function as little as possible, we should choose a red light that activates rod rhodopsin not at all or at least as little as possible. This is best achieved by deep red light in the range above 630 nm."

 

That is part of an article written by Reiner Vogel.

Look here if you need more detail.

 

http://www.reinervog.../vision1_e.html


Edited by Mark SW, 30 March 2023 - 02:54 PM.

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#13 desertstars

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Posted 30 March 2023 - 03:46 PM

NB! If you're observing from a light polluted site, you may never be able to reach levels of dark adaption that allows you to notice the impact a red light can have on dark adaption. 

 

I've found this to be true. I have fairly gentle red lights I put on the clipboard for notes and sketching, and at home (moderately light polluted Tucson, AZ) it presents no problem. But I tell it reduces dark adaptation at a darker observing location. I often need to "rest: my eyes after completing a sketch, and before going on to the next faint fuzzy on the list.


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#14 columbidae

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Posted 30 March 2023 - 03:48 PM

Is there a lower practical limit to dark adaptation? I've noticed that when I use an eye patch over my observing eye, the sky seems to "blow out" after transitioning to the eyepiece. Kind of like a grainy gray color that darkens and smooths out over the course of about 20 seconds. I thought that might just be dark unadaptation, but there's no advantage before it due to the lack of contrast.

#15 Redbetter

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Posted 30 March 2023 - 04:01 PM

My friend with 60 years' observing experience uses an expensive, miserable (…to me…) red light from a reputable astronomics provider to pore at his maps…

I prefer the red/white Coast HX4 flashlight I bought at Canadian Tire for 20 bucks. It provides a wider field of light projection and is significantly brighter, although I can not quote a measurement in lumens for the red light… it is rated at 80 lumens in white…

My friend tells me that even red light can ruin your night vision if it is too bright…

That is not my actual experience.

Is there any actual data or biological plausibility suggesting that red light at a high luminous flux negatively affects night seeing?

Actually, green light is probably better for looking at maps without ruining one's night vision…

https://thehikingaut...r-night-vision/

The quoted article is full of crap.   

 

The author is wrong about green's impact on night vision.  Yes, green is easier to see, both our cones and our rods see it better.  In fact our rods see green light much more effectively than red...and that is not a good thing for night vision.  The fact that our rods see it better means that it is bleaching the rhodopsin in the rods at a much higher rate, damaging night vision.  Green is energy efficient, red is not.  Sure I can use much lower levels or green light than red to perform tasks, but it will still be more damaging to my night vision because its bleaching efficiency is so many times greater.  

 

The military comparisons are off from what I have gathered.  Night vision equipment and lighting isn't designed to maintain maximum unassisted dark adaptation.  It is designed to allow people to detect things with the devices and to perform tasks under low light that they can not perform simply by being fully dark adapted. Red would not be as effective for this, no surprise, but it is a different application and purpose.  (Red is problematic for detecting blood from wounds as well...something one becomes aware of after suffering a simple nick while observing.)   Night vision equipment is passive in that it isn't a flashlight illuminating the target.  Instead it is intensifying the light that is available. 

 

The biggest problem for red as an illumination source is that it is low efficiency even for cone vision.  It takes a lot more red to do the same task, burning through batteries more quickly, and creating a much brighter profile for any sensors looking for it.  But for visual without image intensification red light allows one to keep dark adaptation/sensitivity near maximum.

 

During WWII the Japanese navy excelled at night engagements because of their training, running dark, maintaining maximum dark adaptation and detecting Allied vessels first (all of this interlinked.)  They fired devastating, accurate spreads of torpedoes at long range at their enemies who were completely unaware of their presence.  Then they opened fire with the main batteries, unseen until that time.  The Allies improved over time, but the main improvement was the use of radar and radar gunnery.  This allowed U.S. vessels to see the Japanese approaching and engage accurately with their main guns before the Imperial navy vessels even had visual contact.

 

When folks were scanning battlefields with eyes alone, dim red light was not easily picked up, and it maximized dark adaptation.  But with modern sensors red and near infrared stand out brightly, because they are bright--they are only not bright to our eyes.  What would work for older battlefields has not worked for decades against any modernized foe.


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#16 Redbetter

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Posted 30 March 2023 - 04:28 PM

Is there a lower practical limit to dark adaptation? I've noticed that when I use an eye patch over my observing eye, the sky seems to "blow out" after transitioning to the eyepiece. Kind of like a grainy gray color that darkens and smooths out over the course of about 20 seconds. I thought that might just be dark unadaptation, but there's no advantage before it due to the lack of contrast.

The eye can detect contrast down to ~28 to 29 mpsas, but only for targets of large apparent size.  That is ~250 to 630x darker than pristine night sky (22mpsas.)  The eye itself has a noise level of ~26 mpsas, 40x darker than pristine sky.  That is likely why we can only see 2 - 3 magnitude worse surface brightness than this.

 

The actual background sky (between stars) is even darker, at least 23 mpsas in pristine conditions.  Note that makes it only about 16x darker than the noise level of the fully dark adapted eye. 

 

At the eyepiece, when we use smaller exit pupil/higher magnification, we can see dimmer stellar sources because the background is dimming.  A 2mm exit pupil makes the surrounding field 2.7 magnitude dimmer.  1mm is 4.3 magnitude.  0.5mm is 5.7 magnitude.  At 0.5mm pupil, stellar objects are becoming extended sources (and well before that in poor seeing and/or large aperture.)   Notice that when we switch to the eyepiece, it takes time for our eye to adapt to the now darker sky and we see more as this happens.  Over a few minutes time the adaptation reaches the new equilibrium and we go no deeper.     

 

If you want a good demonstration of the small operating bleach level of our eyes even in very dark skies, try the following:  at a dark site, look for 30 seconds, a minute, or more at some star field above a dark tree line (or other very dark silhouette).  Then look 10 to 20 degrees higher in the sky.  The former "black" silhouette shape will now briefly form the same outline pattern 10 to 20 degrees higher in the sky, but brighter than the sky above that you are looking at.  This brightness fades much in the way you describe.  


Edited by Redbetter, 30 March 2023 - 11:49 PM.

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#17 NathanL

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Posted 30 March 2023 - 04:53 PM

I always observe alone, so if my light bothers me it bothers me and I turn it off.


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#18 TOMDEY

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Posted 30 March 2023 - 05:04 PM

Y1964/65 My very first assignment at the U or Rochester's Visual Science Center (now the renowned Boynton Center) was running "Flash Recovery" experiments on human subjects, otherwise known as Psych Undergrads required to participate as part of their distribution requirements. In my magnificent torture chamber, the subject, constrained ~just so~ would get randomly (to him/her) flashed in the face with a metered blinding light, from not too bad to truck headlight high beam --- then have to search a dim screen for tiny little circles, triangles, or squares... and declare the number seen. I would reward correct responses with nickels drizzled down into their cup --- something like zero to four each iteration... which got progressively harder and harder. I myself was a 17-year-old Igor, already enjoying internship. I complained to the researchers that I needed a punishment solenoid as well; that it might provide better motivation to the subjects. They noted my suggestion, commenting that I was well on the path to becoming a scientist. The rest is history.

 

Anyway, I carry a very dim red light with diffusion added so it looks soft and dim --- and I use it very sparingly. There is also some evidence that very dim other colors may perform as well, to maintain dark adaptation. PS: I've retrofitted many of the lights in my house (and of course the domes) as LED dimmable from nearly zero to bright. The higher end dimmable power supplies and string lights are much more expensive than the usual ones seen around the decorating, Christmas lights. etc. in lighting stores.

 

Here's a fast lens 15-min exposure of my ~Big Dome~ showing the hand rail lights on the surrounding deck. I turn that up until just visible to the dark-adapted. That lets people know where the rail is, but no more than that.    Tom

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  • 06 24-foot dome under stars - original deck railing lights.jpg

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#19 ninelives

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Posted 30 March 2023 - 05:53 PM

I've never used any light at all for setting up or observing, even though I live in a relatively dark area. Like Astrojensen says above, the night sky provides quite a lot of light. I do have good night vision (which my wife complains about, she thinks I should turn on more lights). Of course, if I drop a little focuser screw or end cap on the ground I might change my tune, but that hasn't happened yet! Knock on wood...


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#20 Starman1

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Posted 30 March 2023 - 06:28 PM

My friend with 60 years' observing experience uses an expensive, miserable (…to me…) red light from a reputable astronomics provider to pore at his maps…

I prefer the red/white Coast HX4 flashlight I bought at Canadian Tire for 20 bucks. It provides a wider field of light projection and is significantly brighter, although I can not quote a measurement in lumens for the red light… it is rated at 80 lumens in white…

My friend tells me that even red light can ruin your night vision if it is too bright…

That is not my actual experience.

Is there any actual data or biological plausibility suggesting that red light at a high luminous flux negatively affects night seeing?

Actually, green light is probably better for looking at maps without ruining one's night vision…

https://thehikingaut...r-night-vision/

 

Is there a lower practical limit to dark adaptation? I've noticed that when I use an eye patch over my observing eye, the sky seems to "blow out" after transitioning to the eyepiece. Kind of like a grainy gray color that darkens and smooths out over the course of about 20 seconds. I thought that might just be dark unadaptation, but there's no advantage before it due to the lack of contrast.

Well, there is dark adaptation and there is dark adaptation.

 

You can be dark adapted enough to walk around a telescope field filled with telescopes without a light, and that is what I would call level 1.  You can tolerate level 30-40 of the light level on a Nexus DSC screen.

This takes about 20-30 minutes without a light to see this well.  This improves, I've found, over a few hours.  The idea that you achieve full dark adaptation after 30-45 minutes is contrary to my experience.

 

Then there is the level of dark adaptation you get from walking into the woods and waiting a few minutes until you can make out the path.  That is level 2.

(If you turn around and look at the clearing you came from, it will appear very bright, and it is). IF you can maintain this level, you will be able to tolerate level 10 in brightness on the Nexus DSC screen.

 

Then there is the level you get to with 10 minutes of staring at a black cloth on the ground until you can make out a black eyepiece cap on the black cloth.  That is level 3.

If you glance at the sky for a few seconds, even in very dark skies (21.8+), this level is gone and it takes several minutes to regain it.

When I'm going faint, I transition from the ground directly to the eyepiece without looking around or at the sky and it gains me quite a bit.

The Nexus DSC screen has to be at level 1-5 on the Nexus DSC, but it is, preferably, off.

 

And there is one more level of dark adaptation.  I don't think you can sustain it.  I call it level 4. You go into a closet at home, AFTER you are already dark adapted, in the dark, with no lights on.

You wait until you can see light coming in around the door.  You can begin to see what is around you in the closet from that little bit of light.

You open the door and walk out into the room.  You can feel your pupils contract and the room is almost intolerably bright.  After a few seconds, you no longer have that level of dark adaptation,

and if you return to the closet you are once again blind.

I don't think you can maintain this level of dark adaptation outside a lab environment, though you might be able to approach it with a black cloth over the head that blocks out all peripheral light from every direction.

It would take several minutes, and you would have to be looking through an eyepiece at high power to reduce the field brightness sufficiently.

 

I think that many observers, even those at dark sites, never get past level 1.  Even some of the better observers never get past level 2.

And why would they?  They never look at anything really faint at the very limit of the scope and their visions.

But to achieve level 3 means no light of any kind, red or otherwise--no tablets, red LED lights, and not even any reflective tape on objects around you.

 

What kind of difference can it make?

I experimented with M14 in the summer.  It's horizontal branch centers on magnitude 17.1 (I have a 12.5" scope).

On a normal night at the dark site, I see a slight haze of very faint stars scattered across a round nebulosity on this cluster.

But when I go to the trouble of trying to reach level 3, which takes some time, and I immediately look through the scope, I see hundreds, if not thousands, of stars from edge to edge and the nebulosity is gone

and it resembles a normal globular cluster, only with exceedingly faint stars.

The difference is profound because I have crossed a threshold that allows me to see to, and maybe past, the horizontal branch magnitude.

If I look up at the sky, and trace out a few star patterns, and then look down into the eyepiece again, the hazy nebulous look has returned and I see a scattering of stars across the cluster.

 

So what level of dark adaptation you want to have, or how far you want to push your scope, is up to you, but just be aware that ANY light--the sky, a red LED on dim, or even the light of someone's LED across a field from you--

will negatively affect your night vision.  A too-bright red light is just a sign the observer is not dark adapted, never will be, or doesn't care to be.

By the way, I had a red LED light a few years ago that was 5 lumens on its dimmest setting, and it seemed more than bright enough to see the settings on my Paracorr and the focal lengths on the eyepieces

with the light 15-18" away.  I thought it was quite bright.  These small lights with 200-300 lumens on bright are simply too bright for astronomy use.

So it's not just that the light has to be red, it has to be dim.


Edited by Starman1, 30 March 2023 - 06:40 PM.

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#21 Chad7531

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Posted 30 March 2023 - 07:01 PM

I don’t know, when I first turn my red light on it comes on at the dimmest setting which is what I use. When I turn it off it has to cycle through a few brighter settings and I close my eyes for that.

#22 columbidae

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Posted 30 March 2023 - 07:20 PM

 

What kind of difference can it make?

I experimented with M14 in the summer.  It's horizontal branch centers on magnitude 17.1 (I have a 12.5" scope).

On a normal night at the dark site, I see a slight haze of very faint stars scattered across a round nebulosity on this cluster.

But when I go to the trouble of trying to reach level 3, which takes some time, and I immediately look through the scope, I see hundreds, if not thousands, of stars from edge to edge and the nebulosity is gone

and it resembles a normal globular cluster, only with exceedingly faint stars.

The difference is profound because I have crossed a threshold that allows me to see to, and maybe past, the horizontal branch magnitude.

If I look up at the sky, and trace out a few star patterns, and then look down into the eyepiece again, the hazy nebulous look has returned and I see a scattering of stars across the cluster.

How long do you have before the view in the eyepiece lowers your dark adaptation again?  I suppose it matters if there's anything unreasonably bright in the field of view or not. 
 



#23 sevenofnine

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Posted 30 March 2023 - 08:00 PM

I have dangerous trip hazards at my site. I have to have a bright red light to navigate them. I've found that red light, no matter how bright, reflected off decking or cement has little effect on my dark adaption. It's when red light is reflected off of anything white like charts or a white planisphere then my dark adaption is gone. That's when I use a Rigel Starlite Mini flashlight on it's dimmest setting. Just my own experience...borg.gif


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#24 Starman1

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Posted 30 March 2023 - 08:14 PM

I have dangerous trip hazards at my site. I have to have a bright red light to navigate them. I've found that red light, no matter how bright, reflected off decking or cement has little effect on my dark adaption. It's when red light is reflected off of anything white like charts or a white planisphere then my dark adaption is gone. That's when I use a Rigel Starlite Mini flashlight on it's dimmest setting. Just my own experience...borg.gif

Safety always comes first.


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#25 Alex Swartzinski

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Posted 30 March 2023 - 09:49 PM

 

 

When I'm going faint, I transition from the ground directly to the eyepiece without looking around or at the sky and it gains me quite a bit.

The Nexus DSC screen has to be at level 1-5 on the Nexus DSC, but it is, preferably, off.

 

 

That's really interesting. I think of myself as being dark-adapted when I'm a level two on your scale.

 

As a star hopper, I use the telrad and finder scope to navigate which means I have to look at the sky quite a bit initially. Once I'm on the target, I keep my eye in the eyepiece for several minutes on a faint target. When I pull away from it after a few minutes, my dark adaption is noticeably better until I look at the sky again.

 

Do I get to level three when I stare into a high-power eyepiece for 5-10 minutes? 


Edited by Alex Swartzinski, 30 March 2023 - 09:50 PM.

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