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A method for improving Milky Way exposures in light pollution

• jsjohnst 9y ago
  As a photographer who's shot the Milky Way a lot, I can say this is excellent advice.
• basicplus2 9y ago
  When i was a child all the street and business lights were turned off at about 11pm. Now they are on 24/7 Incredibly wasteful, although i suppose it is safer to go about ones business at night. It certainly gave the opportunity to view the stars even if one lived in city areas.
  • bdamm 9y ago
    Quite recently I lived in a small town far from cities with almost no street lights. I thoroughly enjoyed being able to simply look up and gaze at the glorious Milky Way unaided.
  • russdill 9y ago
    I'm curious if in many decades self driving vehicles will eliminate the need for most night time street lighting.
    • dgsdgdsg 9y ago
      Street lighting predates cars.
• teraflop 9y ago
  While idly thinking about light pollution a while ago, I thought of a ridiculously impractical solution: Mandate the replacement of all outdoor night-time illumination with LEDs that are pulse-width modulated at a low duty cycle. Synchronize them all to an accurate global clock (e.g. from a GPS receiver), so that for instance, all of the lights are simultaneously turned on for the first tenth of each UTC millisecond. Then an image sensor with a sufficiently fast global shutter could disable itself during every brief pulse of light, so that it picks up 90% of the incoming starlight, but almost none of the light pollution.
  • grecy 9y ago
    I think it's time to introduce fines for office buildings that are unoccupied overnight, but have lights on. Certainly in high rise towers this would be tens of thousands of lights. More stars, less energy consumed. Win, win.
    • avian 9y ago
      Slovenia is one of the few countries that has legislation against light pollution. For example, all outdoor lights must only emit towards the ground. It helps a lot with dark skies, but enforcing this kind of rules can be a problem in many cases. http://artificiallightatnight.weebly.com/uploads/3/7/0/5/37053463/mohar.pdf http://artificiallightatnight.weebly.com/uploads/3/7/0/5/370...
      • saiya-jin 9y ago
        THIS so much - Most of the public lights emit in +-all directions, making them not only uneffective but constant light polluters at the same time. And it would be so simple - reflect to the ground, say with 170° angle. this would make the usual 'light cloud' over towns and villages practically disappear. I guess this is a remainder from times where the more light there was, the better (ie look at our mighty civilization and its advances, illuminating whole valleys and soon whole earth!). Now it makes it pretty hard to find unpolluted places in western Europe even in the Alps. I can be in the Italian side of the alps, and I still get orange blobs from Switzerland or France, even across continuous wide range of frikkin' 4000m peaks!
        • ceejayoz 9y ago
          Reflecting to the ground is helpful, but it definitely wouldn't make the light pollution disappear. Plenty would bounce off lightly-colored pavement and back into the sky.
      • dEnigma 9y ago
        Interesting. My hometown in Austria recently installed new lampposts; and all of them are downward-facing. I don't know if this was a conscious decision to reduce light pollution, but it worked wonders. The roads are better lit than before, while there is almost no glare from afar and the night sky is much more visible.
• e12e 9y ago
  Interesting. I would've liked to see the result of 1600 iso at 30s too - just for comparison. On a note about light pollution, the mention of sodium street lamps immediately made me think of filters - stars are suns, so should have wide spectra - why not just filter out the orange bit? Apparently I'm not the first with the idea (obviously): http://www.nezumi.demon.co.uk/nonad/spectra.htm http://www.nezumi.demon.co.uk/nonad/spectra.htm https://petapixel.com/2016/12/14/purenight-filter-cuts-light-pollution-better-night-sky-photos/ https://petapixel.com/2016/12/14/purenight-filter-cuts-light... (has some nice with/without filter images)
  • KaiserPro 9y ago
    my town has just gone to LED now, so its a bit harder to do :/ Still I'm sure one could filter out the peaks from the LEDs (they are phosphor based still) but it's not going to be effective as taking out the sodium notch.
  • lobster_johnson 9y ago
    The PureNight filter is coincidentally a crowdfunded product by Lonely Speck, the people (Ian Norman and Diana Southern) who contributed this story article.
• srrge 9y ago
  This articles reminded me the wonders that surround us while we go on living our boring human lives, so easily forgetting about the marvel of life and nature. Thanks for sharing this.
• anon1253 9y ago
  Or get an IDAS-LPS, CLS or UHC filter (either on the lens or as a sensor clip on). Or stack a bunch of images with proper dark substraction. If you stack enough light sub frames you can efficiently reconstruct dynamic range. Of course the ETTR advice is good too, but you can go much further even with consumer equipment.
• icanhackit 9y ago
  > Shouldn’t the image taken at ISO 6400 show more noise than the image taken at ISO 1600? If the exposures were the same brightness, yes. But these images were not taken with the same exposure. The first image started with twice as much shutter open time (30 seconds versus 15 seconds) and two stops more gain on the sensor (ISO 6400 vs ISO 1600). The result is that the first image has significantly more light data. This makes the final signal-to-noise ratio of the processed images higher on the first image. The higher the signal to noise ratio, the less noisy the resulting photo. So in this case it was actually better to overexpose and compensate later in post processing, despite the initial unprocessed images appearing unusable. This is really neat. I've got a full frame camera with a sensor that has very good dynamic range and I'd learned to under-expose and then pull detail from the shadows in post processing as information can't be saved from blown highlights. This sort of flips that on its head, except the featured overexposed shot didn't have blown highlights, it just looked like it did. Instead it had a wealth of low-light data.
  • kinkrtyavimoodh 9y ago
    That is the right technique in general when overexposing would clip highlights. Here's that's not really a risk, so the other direction works better.
  • hopfenspergerj 9y ago
    ETTR is a real technique to maximize SNR. Underexposing and then boosting shadows is just a good way to guarantee that your image has no contrast, and comes out looking flat and grey all over.
  • michrassena 9y ago
    What I've learned over the years with digital cameras -- you can't trust the preview image. The histogram tells much more of the story (if not the whole truth). My photographs have become much better (in a technical sense) after I learned to expose almost to the point of blowing highlights, making sure there is little blank space at the right (where the highlights are displayed) of the histogram as possible (hence the term Expose To The Right). As someone downthread stated, this improves the signal-to-noise ratio of the captured data. There's an unwritten assumption that the camera's built-in auto-exposure capability isn't sophisticated enough to expose the scene properly, and the photographer has to take control. This is often the case. And speaking of SNR, there are a few tricks astro-photographers have been using for years that occasionally find their way into mainstream photography. One is image stacking, where you combine multiple photographs of the same scene (useful for landscapes if a little blur isn't a problem for you) into a single image. This pushes the shot noise (the random distribution of noise) down even further. I've gotten clean images out of cheap cameras, and even from cheap cell phone cameras (given enough images). The other technique is dark frame subtraction, where you take an photo with the lens covered at the same ISO/shutter/aperture as the rest of the set. Digital sensors have readout noise and heat noise which tends to be very predicable. Subtracting this noise gives you a cleaner shot as well. On a side note, I do wish when talking about ETTR and even digital photography in general that the term "overexpose" wasn't used when explaining the technique of overriding the cameras default metering with exposure compensation. Overexposure would be blowing the highlights, or at least the highlights of details that the photographer considers important (e.g. blowing the highlights of street lights is usually okay). The "over" portion makes it sound like the photographer is doing too much of something, when in reality ETTR is a technique of giving enough exposure, but not too much.
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• sickrumbear 9y ago
  Resource limit reached, anyone have a cached version?
  • lifthrasiir 9y ago
    https://web.archive.org/web/20170912050030/www.lonelyspeck.com/the-milky-way-in-los-angeles-light-pollution/ https://web.archive.org/web/20170912050030/www.lonelyspeck.c...
• StavrosK 9y ago
  Here's something I've wondered about a lot, but haven't been able to find a definitive answer: Isn't ISO pretty much software gain control? Why ever increase the ISO on the camera instead of just taking photos at the native ISO and then post-processing the photo to a higher exposure? That way, you don't store the blown-out pixels (if you do overexpose).
  • micheljansen 9y ago
    No the ISO setting works in the analog domain, amplifying the signal prior to digitisation, so it is different from digital postprocessing. Edit: apparently my knowledge on this is outdated.
    • hug 9y ago
      You had it right the first time. ISO on most cameras is very much implemented via analog gain up to a certain point, beyond which "digital gain" is applied.
      • Aeolos 9y ago
        One thing to note is that most cameras use 12 or 14 bit sensors, so in-sensor digital gain can still be better than post-processing.
        • StavrosK 9y ago
          You mean if you shoot JPEG, right?
          • hug 9y ago
            About the only camera that I know of that will currently saturate the bitdepth of a 14-bit ADC/RAW with DR at base ISO is a Sony A7S II, so right now, yeah, shooting in JPEG is the real issue. This will change in the next few years. If you're the kind of guy who wants to read the relatively dry writings of someone who spends a whole lot of time figuring this stuff out, the following link might interest you: http://clarkvision.com/articles/digital.sensor.performance.summary/#dynamic_range http://clarkvision.com/articles/digital.sensor.performance.s...
• johndoe90 9y ago
  I wonder where are the star trails. Wouldn't 30s exposure make earth movement noticeable?
  • hug 9y ago
    The answer is the 500 rule. To avoid star trails, exposures should be less than 500/focal-length-in-135-equivalent. In other words, if he shot this on his 'favourite' Rokinon 24mm, an exposure time of 20 seconds is reasonable to avoid all star trails.
    • johndoe90 9y ago
      Didn't know that one. Thanks a lot!
• bemmu 9y ago
  I have trouble visualizing how the view of the Milky Way as seen from Earth reconciles with pictures showing whole galaxies. Are we seeing it edge on? Is there any cool animation showing it first from the outside, then rotated to match how we see it in the sky from Earth?
  • pc86 9y ago
    My understanding is that based on the position of the Earth, most of the time what we see is the next band over, from our position on the edge of a neighboring band. But like you I've had trouble finding a detailed explanation of our exact POV within the galaxy.
  • mutagen 9y ago
    Some quick digging found
  • herodotus 9y ago
    Imagine a vinyl record, and that you are sitting on the record, near, but not at, the outer edge of the record. South of you, but close to the horizon, is the centre of the record - containing a massive black hole. North of you are all the stars in the galaxy between you and the edge of the galaxy. Most of the stars in the galaxy are scattered along the disc, but with a fairly large variation. The closer you get to the centre, the greater the number of stars - that is the brightest part of our night sky. Some ancient clusters of stars have drifted a fair bit away from the disc, but are still gravitationally bound to it, and its dark matter. If you were on another galaxy looking from above, our galaxy would look like a spiral with arms. If you looked edge on, it would look more like a cigar.
• michrassena 9y ago
  I'm quite surprised any images of the Milky Way are possible in such a light polluted environment and I'll be using these techniques when I can to see if I can replicate the results.
• A_No_Name_Mouse 9y ago
  Would it be possible to filter out the pollution by subtracting an out of focus image from the in focus one? The pollution is already spread out while the stars are point light sources. So wouldn't that leave the stars untouched while greatly reducing the light pollution?
  • vlasev 9y ago
    All you need to do is make a copy of your image, blur that copy enough to get rid of the stars, and then subtract it from the other image. It's going to affect larger structures like the milky way, though.
• avenoir 9y ago
  Overexposing and underexposing (formally known as Bracketing) is typically a great technique in landscape photography too because it captures as much of the dynamic range as possible. Most DSLRs can bracket right out of the box. Set it up to take 3 exposures (1 underexposed, 1 normal and 1 overexposed) with about 2 or 3 stops in between. Then merge all 3 exposures in Photoshop and you'll get an image with a TON of information embedded in it for you to tweak in post-processing. Also, while I have't tried this, I'd think that using an ND filter in light-polluted areas like this could help a little bit with astrophotography.
  • js2 9y ago
    There are light pollution reduction filters made specifically for astrophotography. I was shocked at how good these photos were w/o using such a filter. I don't think you ever could have recovered so much of milky way using film w/o a filter in such a polluted sky. (I was certainly never able to.) Googling for an example, amusingly enough, the first link is to the same site: https://www.lonelyspeck.com/hoya-intensifier-review-an-affordable-light-pollution-filter-for-astrophotography/ https://www.lonelyspeck.com/hoya-intensifier-review-an-affor... That filter is not specifically for astrophotography, just one that happens to work well. Here's a discussion of other options: https://www.cloudynights.com/topic/494162-light-pollution-filter/ https://www.cloudynights.com/topic/494162-light-pollution-fi...
  • lobster_johnson 9y ago
    Adobe Lightroom can also merge bracketed RAW (DNG) images. That is, you take N DNG images and you get 1 DNG image out, which then preserves more image information that allows you to non-destructively edit the final image. It's available under "Photo Merge > HDR". Unfortunately, it doesn't provide a lot of settings to tweak the merging algorithm, unfortunately.
• Florin_Andrei 9y ago
  If you're into deep space astrophotography, this is not really news. It's all about exposing for the stuff you care about. When imaging DSOs (deep space objects), you often don't care about the relatively bright stars nearby. But you do care about that faint little object in between. So you adjust exposure so the stars are usually blown out (overexposed), but the DSO along with the light pollution background have peeled off the left hand edge of the histogram. So now your DSO is sitting comfortably in the middle of the histogram, where you can process and extract it easily. In practical terms, for DSOs you tweak exposure until the big light pollution hump on the histogram becomes disconnected from the left hand edge of the graph. Turn exposure up gradually until there's a gap at the left hand wall. That usually does it. Overexposure is bad, but underexposure is super-duper-evil, so you must avoid it. OTOH, don't push things too far to the right - you still want some chroma info in the star halos.