80 replies to this topic

[fdboucher]

I’m having some fun here…

I found this magnifying glass with USB rechargeable battery and 6 LED lights on Amazon. It has a clamp & arm that I can use to attach to my EPs table, and study star maps with at least one free hand.

 

Interestingly, the magnifier is pretty good-quality glass. Nice!

 

More interestingly, though, the six LED lights sit behind a plastic ring, secured by four small Phillips screws. That ring is easily detached from the apparatus, and I painted it with two thick layers of 1104CA Dark Red Testor’s model enamel, from my long-ago days as a model hobbyist. (…I fully expected that paint to be bone-dry, but Testor’s make fine 7 mL paint containers!).

 

Looks good, up to now.

 

Is it dim enough?

 

RN Clark, a physicist, photographer and astrophotographer (Yes: The RN Clark who wrote "Visual Astronomy of the Deep Sky"), offers an "Observing Light Standard For Visual Astronomy of the Night Sky" here:

 

https://clarkvision..../obslight1.html

Under his recommended settings, my face-on light, at the lowest of its three brightness levels, registers ⅕ second at ISO1000 - ƒ8.0, and ⅛ second at ISO1600 - ƒ8.0 on my Canon G7x. Just a bit too bright, I guess.

 

(FAR too bright, indeed…)

 

So, I think I will have to add some more lacquer, likely directly to the LEDs (black, on a few, maybe?), in order to avoid annoying my sky-contemplating friend!  

 

Can anyone here lend me his spectrograph? Thx!

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Edited by fdboucher, 03 April 2023 - 09:24 PM.

[ButterFly]

Getting rid of a few of the LEDs is also an option. Skipping the arm can also help. When the LED is closer to the page like that, you don't need much light at all. My flashlight has a single red LED and starts at nothing on the way up. I adjust the brightness with the distance most often. It also keeps the beam smaller so the whole page isn't lit up, but rather, only the small area I actually need.

[fdboucher]

Skipping the arm can also help.

Well, the idea is freeing my hands…  While being able to read a standard star map on the table without wearing my eyeglasses…

Edited by fdboucher, 03 April 2023 - 09:29 PM.

[ButterFly]

Get a music stand that lies closer to flat and adjusts to a low height. Where are you keeping your chart now?

Gravity will work in your favor. If it still skids, put a rubber Oring under it, if you can find one that big. A few rubber spots will work just as well if you can't find the big Oring.

[Redbetter]

 

RN Clark, a physicist, photographer and astrophotographer (Yes: The RN Clark who wrote "Visual Astronomy of the Deep Sky"), offers an "Observing Light Standard For Visual Astronomy of the Night Sky" here:

 

https://clarkvision..../obslight1.html

Under his recommended settings, my face-on light, at the lowest of its three brightness levels, registers ⅕ second at ISO1000 - ƒ8.0, and ⅛ second at ISO1600 - ƒ8.0 on my Canon G7x. Just a bit too bright, I guess.

 

(FAR too bright, indeed…)

While there is some good in the book, Clark's work has some problems, at least the excerpts I have read.  This appears another example, because wavelength matters far more than he states.  He falls into the same trap that every one of these-amber promoting articles falls into:  he neglects to evaluate the ratio of scotopic response (bleaching) to photopic response (cone vision) at the wavelength.    One could actually demonstrate the error in that with his own chart and I have done that before several times with others' charts that made the same exact judgment error that Clark made.  

 

There are other charts and sources that provide better numerical info on the red end. For the numerical info I used earlier I pulled data from the C.I.E. luminous efficiency functions for photopic and scotopic conditions (I have made spreadsheets with 1 nm response factors.) 

 

Other than those with problems with their red cone vision (and those lacking functional L cones/opsin at all), red has a vastly lower bleaching potential, even when many times brighter.  This bleaching is what is harmful to dark adaptation, and specifically why red was chosen so that people could take advantage of cone vision without doing much damage to night vision.  It isn't a case of "any hue will do just as well, except blue" as Clark claims.  

 

Clark mentions using yellow or orange, and is anti-red.  Yellow is ~570nm and the photopic response is nearly 1, which is ~15 times better than 660 red for cone vision.  Unfortunately the scotopic response is 0.2 as well, meaning that the light will do a pretty good job of bleaching rhodopsin.  Indeed this bleaching of rhodopsin is probably contributing to higher sensitivity while using the light, because one will be burning through it at a rate of ~660x greater than with 660nm red. 

 

The "good news" is that the photopic efficiency of the yellow is ~15 times better, so one might expect to turn the red 15 times brighter (although it would not appear that much brighter) to achieve the same level of apparent illumination to the cones.   The problem is that crunching the numbers reveals that, when used over the same length of time for the same apparent illumination, the yellow would bleach about ~45x more rhodopsin.   Light amber would be 17x more, while dark amber/reddish orange is only about 4x more.  

 

Red takes more power and more light for the eye to see.  That poor energy efficiency is a big negative.  I see it during set up/take down if using the orangish backpacking lights vs. using their white light settings on the dimmest level.  When nobody else is around I set up and take down with dim white to save batteries and make the task easier.  But once I am through initial set up it is red (true red) as needed for charts/reading/writing. 

[russell23]

The "good news" is that the photopic efficiency of the yellow is ~15 times better, so one might expect to turn the red 15 times brighter (although it would not appear that much brighter) to achieve the same level of apparent illumination to the cones.   The problem is that crunching the numbers reveals that, when used over the same length of time for the same apparent illumination, the yellow would bleach about ~45x more rhodopsin.   Light amber would be 17x more, while dark amber/reddish orange is only about 4x more. 

 

Red takes more power and more light for the eye to see.  That poor energy efficiency is a big negative.  I see it during set up/take down if using the orangish backpacking lights vs. using their white light settings on the dimmest level.  When nobody else is around I set up and take down with dim white to save batteries and make the task easier.  But once I am through initial set up it is red (true red) as needed for charts/reading/writing.

 

This was definitely a helpful post.  The part in bold perhaps provides the final clues to the discrepancy between your experience and those of us that find amber is better.  I can use a lower illumination level with amber light than red.  I also use that lower illumination for significantly less time because I struggle to read with the red even with the higher illumination and so it takes me longer to study the charts with red light.

 

So the factors you provide (4 - 17x more depending upon the amber spectrum) are based upon the same illumination for the same amount of time.  But the way I use the flashlights then those bleaching factors will be too high because I am using the amber at lower illumination for less time.  My actual field experience is therefore that the impact on night vision is in fact less when I use the amber flashlights.

[Jon Isaacs]

This was definitely a helpful post.  The part in bold perhaps provides the final clues to the discrepancy between your experience and those of us that find amber is better.  I can use a lower illumination level with amber light than red.  I also use that lower illumination for significantly less time because I struggle to read with the red even with the higher illumination and so it takes me longer to study the charts with red light.

 

So the factors you provide (4 - 17x more depending upon the amber spectrum) are based upon the same illumination for the same amount of time.  But the way I use the flashlights then those bleaching factors will be too high because I am using the amber at lower illumination for less time.  My actual field experience is therefore that the impact on night vision is in fact less when I use the amber flashlights.

 

I believe Red's point is that the bleaching of the rhodopsin occurs much more rapidly with the amber light..

 

I know Red as someone who observes 17th magnitude galaxies in his 20 inch.  He investigates the visual noise floor (dimmest distinguishable gray) He's very serious about being fully dark adapted.

 

My questions for those involved in this discussion:

 

- How dark are your skies?

 

- What objects do you typical observe?  In particular, how often do you observe low contrast, low surface brightness nebulae and galaxies?

 

Large regions of nebulosity like Barnard's loop and the IC1805/IC1848 region (Heart and Soul) can be observed without relying on charts. Many low contrast, low surface brightness, difficult objects can be observed from memory so one can spend an evening without using any artificial light.

 

This gives a base line for comparison with the use of light for reading charts..

 

Jon

[Starman1]

You guys that use amber must just not achieve a high level of dark adaptation.

I find the Rigel Starlite flashlight too bright on its dimmest setting, so I use a Starlite Mini that can be used even dimmer.

95% of the time at a dark site, I have no lights on at all--it requires no light to choose an eyepiece in a case.

I even keep the screen on my DSC at a level low enough I need to be a foot away to tell it's on, and then it shuts off automatically after a minute.

You can train yourself to be able to read and write notes under very low red light.

[russell23]

I believe Red's point is that the bleaching of the rhodopsin occurs much more rapidly with the amber light..

 

I know Red as someone who observes 17th magnitude galaxies in his 20 inch.  He investigates the visual noise floor (dimmest distinguishable gray) He's very serious about being fully dark adapted.

 

My questions for those involved in this discussion:

 

- How dark are your skies?

 

- What objects do you typical observe?  In particular, how often do you observe low contrast, low surface brightness nebulae and galaxies?

 

Large regions of nebulosity like Barnard's loop and the IC1805/IC1848 region (Heart and Soul) can be observed without relying on charts. Many low contrast, low surface brightness, difficult objects can be observed from memory so one can spend an evening without using any artificial light.

 

This gives a base line for comparison with the use of light for reading charts..

 

Jon

I understand Reds point.  It is more complicated than you characterized it.  Amber light bleaches more rapidly at a given intensity.  The variables are not just the light color, but also the duration of exposure and the intensity of exposure. 

 

I live in rural upstate NY.  My skies are darker at my new house I moved to over a year ago.  The old house had problems with southern sky light pollution from a scrap metal facility just a couple miles away.   The new house has none of that.  But taking out that light pollution source the background level of sky darkness/brightness is about the same as the old house. 

 

I don’t measure my sky brightness.  I don’t have the equipment to do that and I don’t really care.  I observe with the skies I have - whatever those are.   What I do know is that my new house sits on the darkest land in my county based upon the light pollution maps. 

 

You guys that use amber must just not achieve a high level of dark adaptation.

I find the Rigel Starlite flashlight too bright on its dimmest setting, so I use a Starlite Mini that can be used even dimmer.

95% of the time at a dark site, I have no lights on at all--it requires no light to choose an eyepiece in a case.

I even keep the screen on my DSC at a level low enough I need to be a foot away to tell it's on, and then it shuts off automatically after a minute.

You can train yourself to be able to read and write notes under very low red light.

That may be. I’m not observing out in the dark western mountains.  I’m in the rural northeast US. 

 

I can see just fine in the dark.  I don’t ever use a light unless I’m looking at a chart - which I don’t do that often.  But when I do look at a chart I have trouble reading it in bright red light.  I have no trouble reading it in dim amber light.  

 

Regardless of all that - it is a fact, that my night vision recovers much more rapidly when I use the dim amber light vs. when I use the brighter red light.  So whatever level of dark adaptation my eyes are getting to, the dim amber light is doing less damage to it than the brighter red light. 

 

And switching to a dimmer red light won’t improve things.  If I struggle to read charts with a brighter red light after hours of observing, then how would I find it easier to read with a dimmer level of red? 

[fdboucher]

If everyone had identical eyeballs, then Redbetter's referenced "table of normalized scotopic (rod) response" would be very applicable.  BUT, that is just NOT correct.  Some people are color-blind, others have extra color receptors, and still others have differing amounts of each type of receptor, thus varying one's sensitivities to the effects of light wavelengths.  What is "poppycock/false narrative" is that everyone's eyes are identical, matching studies that provide average responses.

It is a known fact that there are different color perceptions in different people. I'm not 100% positive, but I believe that Redbetter's table is derived from in vitro studies on cultured cells or ex vivo retinas.

Now, the vision chain resulting in light and color perception is complex. I quote:

 

"Color vision deficiency can result from a variety of abnormalities, both systemic and specifically within the visual system. Defects in the genes responsible for visual transduction often lead to congenital color vision deficits. Any abnormalities of the retina, optic nerve, optic tract, and visual cortex can cause defects in color vision. As such, systemic diseases like diabetes can alter color vision, as can eye-specific diseases like glaucoma and cataracts." https://www.ncbi.nlm...ooks/NBK544355/

 

There are many genetic, neurological chemical and optical causes for dyschromatopsia. (Read the paper: it's excellent).

So it is not unreasonable to assume that some of our sky-observing friends may prefer amber light to red for good reasons. It would be fascinating to perform a study of color perception and scotoptic recovery comparing experienced observers with different preferences for dark light.

Maybe they eat more carrots and cod liver oil? Maybe these people are protanopic, or just protanomalous (1-2% of Northern European origin  males are, apparently…)? 

 

https://www.visionce...olor-blindness/

https://tinyurl.com/3kf7jcz4

https://tinyurl.com/w9hbsw9n  (Outstanding short review!)

 

In short: protanomalous subjects have a congenital decrease in sensitivity to red light. This is NOT Daltonism (an ancient term… now called congenital red–green color blindness).

 

https://www.nei.nih....color-blindness

 

There are different diagnostic instruments to detect dyschromatopsia, but the most used in a clinical setting is the Color Perception Test, also known as Ishihara test. Spectral anomaloscopy is the standard reference test for diagnosing red-green color vision defects. It is used in research. A genomic test may identify the cause if it is related to mutations in OPN1LW or, less likely, OPN1MW genes on Chromosome X. Most interestingly, females who are heterozygotic for different mutations of these opsin genes may present with enhanced color perception.

 

However, there are many other, non-genetic, causes to dyschromatopsia. 

 

I suggest you guys who prefer amber light order a T-shirt saying: "Don't Mess With Me! I'm Protanomalous" in large, very RED letters, and wear it to star parties everywhere… 

Edited by fdboucher, 04 April 2023 - 05:06 PM.

[Jon Isaacs]

 

I understand Reds point. It is more complicated than you characterized it. Amber light bleaches more rapidly at a given intensity. The variables are not just the light color, but also the duration of exposure and the intensity of exposure. 

 

The issue is the relationship between the increased bleaching and the sensitivity.  Red covered that..

 

What sorts of objects are you observing?  I think it's important to establish some sort of baseline for comparison between the various members involved in this discussion.

 

What does lightpollutionmaps.info say about your observing site? In my experience it predicts the skies will be darker than I measure but it does provide a relative measure.

 

The map indicates my site is 21.64 mpsas but it varies from 21.0 to 21.4 mpsas with the darkest ever being 21.54 mpsas on a night when lower elevations were under heavy cloud cover. The most recent trip to a more remote location was given 21.96 mpsas by light pollution maps but I measured 21.6 to 21.7 mpsas. 

 

I observe objects of all types but under ideal conditions, I often observe large faint objects like Barnard's loop using large exit pupils and H-Beta and O-lll filters. These darken the sky by about 3 magnitudes placing a premium on dark adaptation. 

 

I use a tablet with a deep red screen filter adjusted to the screen brightness measures at least a half magnitude darker than the sky with the SQM.

 

I have not experimented with other colors. Rather I base my use of deep red based on the photo chemistry as well as what observer's like Don Pensack, Redbetter and Dave Knisely are using. They make difficult observations that are remarkable when I compare them to what I'm able to do. 

 

I observe a great deal and often work from memory for an entire night. With my tablet with it's screen covered by a deep red film an adjusted so I can barely read it, it seems to have little effect on my night vision. I suspect Don would find it too bright.

 

Jon

[ButterFly]

 

I have not experimented with other colors.

That's all that matters.

[gwlee]

For me, that is related to font size.

For my in-the-field charts and observing lists, I print at 14pt type.

I can keep the red light very very dim--dimmer than setting one on the Rigel Starlite--and still read the print.

This rural mountain site is fairly dark, but requires a lot of tree dodging, so I prefer to thoroughly work the same small section of the sky (~10°) with a minimum of observing paraphernalia for several hours each night for about a week before moving on. Studying a chart for a few minutes before and after each observing session allows me get along without a chart, a light to illuminate it, or a table to put them on, and preserves my night adaptation. 

 

At first it was difficult because I had used charts for decades and become dependent on them rather than my short term memory. I get lost occasionally, can’t find something, or don’t recognize what I am looking at, but sort it before the following night. This approach wouldn’t work if I was trying to work the whole sky every night. 

[Redbetter]

This was definitely a helpful post.  The part in bold perhaps provides the final clues to the discrepancy between your experience and those of us that find amber is better.  I can use a lower illumination level with amber light than red.  I also use that lower illumination for significantly less time because I struggle to read with the red even with the higher illumination and so it takes me longer to study the charts with red light.

 

So the factors you provide (4 - 17x more depending upon the amber spectrum) are based upon the same illumination for the same amount of time.  But the way I use the flashlights then those bleaching factors will be too high because I am using the amber at lower illumination for less time.  My actual field experience is therefore that the impact on night vision is in fact less when I use the amber flashlights.

 

That isn't for the same illumination though, that was/is my point.    It is for the same apparent (photopic) level of illumination as we would see it.   At 620nm (which is deeper orange red) that would require 6.3 times as much red light at 660nm; but we wouldn't see it as 6.3 times brighter, it would appear to be roughly the same intensity in cone vision which is what we use to read/see things at small scale.  The scotopic response at the two wavelengths varies by a much larger factor:  23.5x.  That is the root problem, because for equivalent photopic (cone) response by the average eye, 23.5/6.3 = 3.7 (which I simplified to 4) times as much bleaching will happen.   

 

You've got to really blast the red and/or for a long time to overcome that and bleach badly with the red as you describe.  I'm not saying that people don't do that.  My experience, like others, is that when I can't read something under marginal illumination, I turn up the light.  Poor use/dispersion of the light is often more of a problem than the wavelength, as I have seen with amber/orange lights.  It I try to use a headlamp I am creating a much larger, overall brighter field of view.  But using a properly designed red LED close to the page presents higher intensity over a smaller visual field, resulting in the acuity needed for fine print.  

 

The potential damage from the red depends on the spectrum, intensity, and time (as with other wavelengths).  I can only approximately measure the red surface brightness.  The SQML is designed to measure lighting with a response similar to photopic.  However, there is somewhat of a red leak reported for the lens/filter so that it reads brighter than it should for the red when reporting photopic values--an issue with replacement of yellower light sources with bluer ones in terms of light pollution. 

 

Like I said, I did a test of this with an SQML meter in the garage to get an idea of the red light level I needed to read fine print.  Holding the meter at similar distances as my eye showed that it was reading in the high 14's to high 15's.  Some correction would be needed for the wavelength to represent photopic illumination levels, which if all the red light passed (1.0 factor) would be perhaps 2 but not quite 3 magnitude stronger signal.  It is hard to say how much since the overall wavelength response factor for photopic would not be 1.0 either, but a somewhat lower factor.  My best guess is that the different impacts would result in a correction of no greater than 2 magnitude.   That puts the meter reading at 12.8 mpsas for what I consider more than sufficient reading level for NGC #'s in Uranometria charts.   That sounds really bright and it would be bright if it was green or yellow or light amber light (590nm), but at 660nm it is closer to 21.6 mpsas equivalent in terms of scotopic (rod) response. 

 

So the question I have is what light level is being used to read fine print with an amber light (and what characteristic wavelength.)  There should be very little (if any) meter correction needed for 590nm light, since the photopic response is 0.812.   There would be be an adjustment for scotopic equivalence of the wavelength (~3.3 at 590nm vs. ~8.8 for 660nm.)  If a person did an experiment like I did with an SQML and their amber light, what would the meter read pointed at the page at roughly the same distance as their eyes, with the light held at the normal position they use for reading charts.  Are they reading the print on the chart as dark as 18.3 mpsas per the meter?  [Note that I am not using 620 nm, as that is closer to what the pseudo red LED's are calling red, I doubt it is being passed off as amber, but I could be wrong.]

[Redbetter]

You guys that use amber must just not achieve a high level of dark adaptation.

I find the Rigel Starlite flashlight too bright on its dimmest setting, so I use a Starlite Mini that can be used even dimmer.

95% of the time at a dark site, I have no lights on at all--it requires no light to choose an eyepiece in a case.

I even keep the screen on my DSC at a level low enough I need to be a foot away to tell it's on, and then it shuts off automatically after a minute.

You can train yourself to be able to read and write notes under very low red light.

I tend to use higher light levels for writing notes...otherwise I can't read the notes when I get back home.     But part of that is that the surface I am writing on compresses too much--it is paper in a thick observation binder.  That compression of the paper makes pencil position more approximate than normal.  I need to rectify that and start taking each nights notes with a clip board.  I have used a clip board when trying to make good sketches rather than very approximate ones in notes.  But I get in the habit of just adding new blank sheets to my thick binder--and periodically moving older observations to binder logs.  I need to break out of this habit.  

 

One place where Clark's comments about other, yellower colors are more useful is when sketching, particularly if trying to capture some color.  Even for black and white, finer control in sketching/shading does require more light to capture adequately, but there is a penalty to be paid and it takes me longer to re-adapt at the eyepiece.  The main area where color matters more is planetary, and dark adaptation is not necessary for that.  

[columbidae]

One of these days I'll invent a device that quickly covers my observing eye for when I'm down at my logbook/charts, and then separately covers my writing/sketching eye for when I'm at the eyepiece.  Or would my brain still bother my eyepiece view with ghost images from the light from my other eye? 

[ButterFly]

One of these days I'll invent a device that quickly covers my observing eye for when I'm down at my logbook/charts, and then separately covers my writing/sketching eye for when I'm at the eyepiece.  Or would my brain still bother my eyepiece view with ghost images from the light from my other eye? 

I just use my hand.

 

It is interesting that there are brain afterimages and eye afterimages.  Give it a try for yourself.  Burning out the photopic vision in one eye affects how my other eye perceives that which it senses.  It would be great if we could stop the analysis at the eye and just treat it like a camera.  Unfortunately, the eye is the worst part of the eye brain system.  And our brains lie to us too!  Hypothetical average eyes don't exist, but if they do, they're not on my face.

 

Sketching is the most challenging for me.  I still need to light up the whole sheet to avoid a wonky product.  I get weird skews developing if I try t light up one section at a time.  I use one of those red conductor lights, with several added layers of taillight tape.  I clip that onto my sketchpad.  It still takes me a few moments to recover back at the eyepiece.

[russell23]

I did another experiment tonight.  I realized there is a room in the house that gets absolutely no light.  The door is so tightly framed that you might as well be in a steel box.  When in this room with its lights off you can't see anything - just whatever random signals your visual system sends you trying to see anything at all.

 

So I brought in my atlas and the two flashlights.  When I turned on a light I held it and scanned around for 20 seconds then I shut it off, watched how my vision reacted, and timed how long it took for the random visual background to return to what it was before I turned on the light.  Then I waited and repeated with the other color.  I went back and forth with this procedure for 4 cycles or 8x I turned on a flashlight.

 

With the Amber light the first time I did this the recovery time was 20 seconds whereas with the red light it was 30 seconds.  By the 4th cycle the recovery time was 40 seconds with the amber light and 60 seconds with the red light.   So the more times I did this the longer the recovery time  but the recovery was approximately 50% longer with the red light.

 

But what was also interesting was how the recovery looked.  With the amber light it took 5 seconds for a faint grayish yellow "cloud" to appear in my vision.  By about 15 seconds this was dramatically fading and then it was just a matter of scanning until I felt the background visual noise had returned to what it was before. 

 

With the red light it again took 5 seconds for a "cloud" to appear after shutting the light off.  But the cloud in this case became a bright blue cloud - much more intense than the gray yellow cloud associated with the amber light and extending over a larger range of my vision.  This cloud was noticeably bright for 15-20 seconds.  The blue color remained past the stage where it was a bright visual cloud, but was gone a few seconds before I felt my vision had returned to normal. So the first time I turned on the red light the blue color lasted for ~25 seconds and the apparent recovery to background visual noise was at 30 - 33 seconds.

 

In actual observing circumstances I am not in a totally dark room because the sky provides enough light to see by when adapted to the dark.  But this experiment matches my experience outside - except that if I use a red light I have to shine it for longer on the charts than the amber light so the discrepancy in outcome would be even worse for the red light.

[ButterFly]

Doing that same experiment after your done observing for the night is probably a more reliable indicator to go by.  Afterimages are always clearing away.  I wouldn't be surprised if there were different results after several hours in that room.  Bring an audio book next time?

 

It's so odd that afterimages are different colors.  The brain is a wonderful thing at times.  Perhaps the color that afterimages to blue in our cortex affects whether we still perceive the blue from our rods.  I wonder what that color is for me?

[Starman1]

One of these days I'll invent a device that quickly covers my observing eye for when I'm down at my logbook/charts, and then separately covers my writing/sketching eye for when I'm at the eyepiece.  Or would my brain still bother my eyepiece view with ghost images from the light from my other eye? 

It's called an eyepatch.  Flip it up to uncover the eye and flip it down to cover the eye.

People think pirates lost their eyes a lot, since the quintessential pirate has an eye patch.

But pirates that manned the deck at night would cover one eye when they went below to get food or water,

and flip it up when they came back to the deck so they wouldn't be night-blind and stumble around.

The covered eye retained its dark adaptation.

[havasman]

Spend an hour at the eyepiece, with a high magnification (darker field) with a hood over your head, and you'll see at least a magnitude deeper.

 

But, importantly, the sky was about 21.7 SQM and you could walk around with out a torch. So the 'high' ambient light was preventing full DA anyway.

 

Patient observing over a reasonable amount of time under an observing (monk's) hood is the way to go for me for sure if I intend to see the faint details in some interesting object or a faint object. My Nexus DSC's are still on the default 30 minute time-out setting and at first they were often unexpectedly dark when I'd come out from under the hood. I've gotten used to it. It is seldom dark enough anywhere I observe but some of Big Bend to get dark adapted any way but under a hood.

 

Back when DSA still made these they had pics of some astro monks in their hoods. The length blocks A LOT of light when you mold it around the ep or focuser. You just have to plan a path for your breath.

 

It has been very difficult to convince folks they do not need lights to walk the observing field at the club dark site w/o their lights and certainly not those stupid bright headlights. But you don't. Even if the feral hogs have been at it you can pick a safe footfall across the ground with no light but what comes from the sky.

 

Lights? Mostly none. Rigel Starlite mini set low for general use around the scope or pad. Ken Fiscus light for charts. All are red. If nobody else is present or observing when I end a session I'll sometimes use part of the red LED strip on a NEBO Slyde King 2 to pack up but it'd be crazy to use any other time.

Edited by havasman, 05 April 2023 - 03:13 AM.

[Redbetter]

I did another experiment tonight.  I realized there is a room in the house that gets absolutely no light.  The door is so tightly framed that you might as well be in a steel box.  When in this room with its lights off you can't see anything - just whatever random signals your visual system sends you trying to see anything at all.

 

So I brought in my atlas and the two flashlights.  When I turned on a light I held it and scanned around for 20 seconds then I shut it off, watched how my vision reacted, and timed how long it took for the random visual background to return to what it was before I turned on the light.  Then I waited and repeated with the other color.  I went back and forth with this procedure for 4 cycles or 8x I turned on a flashlight.

 

With the Amber light the first time I did this the recovery time was 20 seconds whereas with the red light it was 30 seconds.  By the 4th cycle the recovery time was 40 seconds with the amber light and 60 seconds with the red light.   So the more times I did this the longer the recovery time  but the recovery was approximately 50% longer with the red light.

 

But what was also interesting was how the recovery looked.  With the amber light it took 5 seconds for a faint grayish yellow "cloud" to appear in my vision.  By about 15 seconds this was dramatically fading and then it was just a matter of scanning until I felt the background visual noise had returned to what it was before. 

 

With the red light it again took 5 seconds for a "cloud" to appear after shutting the light off.  But the cloud in this case became a bright blue cloud - much more intense than the gray yellow cloud associated with the amber light and extending over a larger range of my vision.  This cloud was noticeably bright for 15-20 seconds.  The blue color remained past the stage where it was a bright visual cloud, but was gone a few seconds before I felt my vision had returned to normal. So the first time I turned on the red light the blue color lasted for ~25 seconds and the apparent recovery to background visual noise was at 30 - 33 seconds.

 

In actual observing circumstances I am not in a totally dark room because the sky provides enough light to see by when adapted to the dark.  But this experiment matches my experience outside - except that if I use a red light I have to shine it for longer on the charts than the amber light so the discrepancy in outcome would be even worse for the red light.

It sounds like the light you are using is far too bright in either case based on what I have used and observed.  The longer recovery time with repeated exposure suggests accumulating bleach levels.  What lights are you using?

 

I did my own darkroom test tonight to see how my eyes responded.  The room itself is an interior utility room.  With the lights in the house mostly off, and the water heater control display covered with foil & tape, there was only a small amount of light leaking in around the door (dark towel completely blocking the base).  Since the light around the door was a very indirect (2 to 3 reflections) path around the perimeter, it only showed up when looking at it from specific angles.  I tried getting a reading with the SQML pointed at this glow, but it was dimmer than 24 mpsas and did not register.  And of course the room was far dimmer.

 

Since neither the SQM nor SQML could register in conditions this dark, I could only use my visual response to estimate.  After half an hour in the room, I could just barely pick up motion of my arm with navy colored sleeves against the white washer--I couldn't make out either of them, but I could see the approximate shape of my arm.  This was primarily far peripheral vision detection and stronger in my left/observing eye, very weak in my right, so likely in the neighborhood of 27 - 28mpsas.   While I wouldn't have been as deeply dark adapted as when observing in dark skies over several hours, I had been in a room at mesopic light levels for the preceding hour, so the bleach level would have been moderate initially.  

 

So I repeated the tests reading Uranometria galaxy #'s with my red Starlite, measuring surface brightness of the page with the SQML.  I was using what I would call a 3 out of 7 setting since I forgot to bring in my cheaters and needed more light.  This measured about 14.6mpsas.  Brightest setting (7/7 highest on position) measured about 10.6, while the dimmest (1/7 lowest on position) was around 16.2.  There was no apparent after image or glow after reading the charts for over 20 seconds.   I was looking for this but it wasn't there.  

 

I did some testing of the "red" setting on the Blackdiamond Cosmo lamp as well, probably close to the 620nm characteristic level.  This is not quite the newest build of the Cosmo although the "red" LED patch looks the same, and my much older Cosmos are substantially different and slightly redder.  I tried both the high and low setting.  Both levels were brighter than I would have liked.  Despite that I did not see any after image as you described, even on the brightest setting.  The room was too dark for any meaningful test for whether I was losing ability to pick up threshold objects vs. the true red light.

 

The only time I got an after image was at the end turning on the fluorescent for a moment over head.  That brief flash was on purpose and was partially to watch the afterglow of the light itself when I shut it off.  I know from prior tests that if I shield my eyes while it is on instead, and the light has been on for some time (enough to warm) that I can detect its waning afterglow for about a minute, with it averaging out to ~24+ mpsas as read by the meter which just manages to yield a reading before timing out. 

Edited by Redbetter, 06 April 2023 - 05:56 AM.

[Freezout]

It is quite funny to imagine all the participants to this thread ending up locking themselves in the toilets, basements or whatever insulated room of their house to create a "dark room" and fiddling with colored lights, chronometers and notebooks...

[Redbetter]

It is quite funny to imagine all the participants to this thread ending up locking themselves in the toilets, basements or whatever insulated room of their house to create a "dark room" and fiddling with colored lights, chronometers and notebooks...

Some years ago I was documenting some home improvements I had made.  One was changing out some problem toilets with Totos that wouldn't clog (kids bath was first of course) and used less water per flush.  I was curious about how many flushes/day was normal, so I put a simple clip-on pedometer onto the flush lever in the tank to measure for a week.   

 

I also bucket tested some low flow shower heads about the same time.  One was underperforming and the bucket test confirmed it was putting out substantially less than the desired/rated flow.  I contacted the maker, explained my water pressure, and tests, and he identified the problem as being in the orifice material likely deforming due to the pressure.  I confirmed visually that there was some pucker that shouldn't have been.  He sent me some replacement rings that fixed the problem and yielded flows on target which provided a much better shower.  It was a win-win since he hadn't realized the original material would have a problem in this range.  

[Jon Isaacs]

That's all that matters.

 

Actually what matters is that no one is discussing the brightness of their skies, the telescope they're using, the objects they're observing. Red is measuring things and discussing the sensitivity of his eyes in terms of mpsas. 

 

Without a frame of reference, this discussion is mostly apples and oranges..

 

That was the purpose of my post, let's get some context. Does anyone want to share this information?

 

What I find interesting is how much dimmer my tablet reads with the SQM than Red's charts. I'm reading my tablet when it measures 22.0 mpsas and darker from approximately my viewing distance. It has a deep red film made by Sirius Optical so that shifts the numbers a little. I suspect that there's a fundamental difference that explains this.

 

Jon