Worse base ISO with new sensors?

kenw said:

René Schuster said:

Anders W said:

René Schuster said:

Well, Bob, that is just air pollution in Sweden, result: Waldsterben. Or what do you think killed these trees? ;-)

Click to expand...

Sorry to disappoint. But that's not Sweden. It's Yosemite National Park, CA, USA, between Lukens Lake and the White Wolf campground.

Click to expand...

Well, then I guess we have to call it the 'dying forest syndrom'! ;-)

Click to expand...

Otherwise known as the bark beetle. Huge problem in the southwest USA for the past decade or so.

Click to expand...

Ah, my best friend, Ips typographus! With the help of some stormy winds, many little Ips and finally two chainsaws my backyard view is much nicer now than it was three years ago! Forest-neighbor's silly spruce are all gone now and I can enjoy looking down in the valley! :-D

In the US I think it is directly related to rising temperatures, making the beetle move even further north. Dry and warm is what they like.



RS

bobn2 said:

OK, I look to your tests with interest.

Click to expand...

Got some access to blue sky today.

All shot with E-M5 at ISO 200 F/5.6. The test cases are:

• 150mm 1/2000 infinity focus
• 15mm 1/2000 infinity focus
• 15mm 1/2000 close focus
• 15mm 1/5 infinity focus with ND400 filter

So to review, we've shot with an order of magnitude difference in angular resolution as well as physical aperture size, we've shot both infinity focus and close focus and because the claim was made that somehow no one has ever noticed "sky texture" with the human eye despite a few centuries of looking through powerful telescopes and binoculars that perhaps the integration time of the eye was an issue we've also shot at a slower shutter speed one about four times the integration time of the light adapted eye.

If the claims of "sky texture" are to have any merit in experiment (as they clearly have none in theory to begin with) then we should see some sort of difference in these sky patches.

All processed in LR with default processing except NR and sharpening turned off.

I'd label them, but as you can see it doesn't matter - they are all the same as we should expect. EXIF info still there if you want to sort them out a bit more. I also took the time to examine these closely directly in LR in case anything might be masked by the export process for uploading. Again, no difference.

I'm putting the "sky texture" theory to rest now. No theoretical basis, no experimental evidence. Doesn't exist. It is clearly the camera and the processing chain.

























--
Ken W
See profile for equipment list

I cannot agree with the statement that ISO value is first and foremost about protecting the sensor from over exposure although it is certainly correct that, say, doubling the ISO will cause the camera to meter such that the exposure is reduced by one stop giving the sensel one stop in headroom. However, irreversible clipping of the in-camera RAW file occurs equally from an exposure that produces a saturation of the sensel with an ISO determined analogue gain of one as with an exposure that produces 1/2 the analogue sensel electron count and an analogue gain twice as high with a doubling of ISO.

The point I would make is that the purpose of ISO is not to protect or even provide RAW file headroom - an exposure that saturates the sensel and blows the highlights will still blow the highlights in the RAW file wiith double the ISO and half the exposure - but rather to lower the noise floor in cameras which are ISO variant.

First of all, even in ISO-variant cameras, one would only consider increasing the ISO determined analogue gain to lower the read noise floor if compelled to reduce exposure by the ss &/or aperture requirements of a particular scene as any reduction in exposure below that necessary to prevent sensel clipping will unnecessarily reduce the sensel signal which in turn reduces the shot S/N level (the basis for the concept of ETTR) which far outweighs any increase in read S/N that would be gained from increasing ISO.

The ISO variant effect is dependent on the ratio of downstream read noise of the particular camera relative to the upstream read noise component. Doubling the ISO analogue gain results in a doubling of the sensel signal level in the RAW file, but only doubles the upstream read noise (which in ISO variant cameras is small compared to the downstream read noise) leaving the downstream noise unchanged which effectively reduces the overall read noise S/N level (doubling the signal but only doubling the small upstream component of the total noise). This effect continues until one reaches an ISO at which the analogue gain has multiplied the upstream read noise so that it has become the dominant component of the overall read noise. At that point, if the shot still requires a reduction in exposure parameters, then one is better off underexposing in camera and increasing brightness in raw processing rather than increasing ISO analogue gain as changing the tone curve will indeed avoid the possibility of clipping the camera RAW file by affecting brightening with exposure/ISO.

kenw said:

bobn2 said:

OK, I look to your tests with interest.

Click to expand...

Got some access to blue sky today.

All shot with E-M5 at ISO 200 F/5.6. The test cases are:

• 150mm 1/2000 infinity focus
• 15mm 1/2000 infinity focus
• 15mm 1/2000 close focus
• 15mm 1/5 infinity focus with ND400 filter

So to review, we've shot with an order of magnitude difference in angular resolution as well as physical aperture size, we've shot both infinity focus and close focus and because the claim was made that somehow no one has ever noticed "sky texture" with the human eye despite a few centuries of looking through powerful telescopes and binoculars that perhaps the integration time of the eye was an issue we've also shot at a slower shutter speed one about four times the integration time of the light adapted eye.

If the claims of "sky texture" are to have any merit in experiment (as they clearly have none in theory to begin with) then we should see some sort of difference in these sky patches.

All processed in LR with default processing except NR and sharpening turned off.

I'd label them, but as you can see it doesn't matter - they are all the same as we should expect. EXIF info still there if you want to sort them out a bit more. I also took the time to examine these closely directly in LR in case anything might be masked by the export process for uploading. Again, no difference.

I'm putting the "sky texture" theory to rest now. No theoretical basis, no experimental evidence. Doesn't exist. It is clearly the camera and the processing chain.









--
Ken W
See profile for equipment list

Click to expand...

OK, thanks for that. pretty conclusive. My theory bites the dust.

--
Bob
'Technology' is a name that we have for stuff that doesn't work yet.
Douglas Adams.

kenw said:

bobn2 said:

OK, I look to your tests with interest.

Click to expand...

Got some access to blue sky today.

All shot with E-M5 at ISO 200 F/5.6. The test cases are:

• 150mm 1/2000 infinity focus
• 15mm 1/2000 infinity focus
• 15mm 1/2000 close focus
• 15mm 1/5 infinity focus with ND400 filter

So to review, we've shot with an order of magnitude difference in angular resolution as well as physical aperture size, we've shot both infinity focus and close focus and because the claim was made that somehow no one has ever noticed "sky texture" with the human eye despite a few centuries of looking through powerful telescopes and binoculars that perhaps the integration time of the eye was an issue we've also shot at a slower shutter speed one about four times the integration time of the light adapted eye.

If the claims of "sky texture" are to have any merit in experiment (as they clearly have none in theory to begin with) then we should see some sort of difference in these sky patches.

All processed in LR with default processing except NR and sharpening turned off.

I'd label them, but as you can see it doesn't matter - they are all the same as we should expect. EXIF info still there if you want to sort them out a bit more. I also took the time to examine these closely directly in LR in case anything might be masked by the export process for uploading. Again, no difference.

I'm putting the "sky texture" theory to rest now. No theoretical basis, no experimental evidence. Doesn't exist. It is clearly the camera and the processing chain.









--
Ken W
See profile for equipment list

Click to expand...

Can you check the images for any correlation between the noise and the pixel coordinates? I wonder if some pixels have a tendency to be brighter and others to be dimmer.

Pecolpan said:

Can you check the images for any correlation between the noise and the pixel coordinates? I wonder if some pixels have a tendency to be brighter and others to be dimmer.

Click to expand...

Sorry don't have the time at the moment to do that, but the answer to your question is the most certainly some pixels tend to be brighter and some dimmer. It is often called "fixed pattern noise" and is due to the variation in the sensitivity of each pixel. All sensors do this to some degree, the question is it a significant enough difference compared to other noise sources. For the brightness levels of these sky patches the magnitude of the fixed pattern noise is going to be a fair bit lower than the photon shot noise - I'm basing this on the DxO Full SNR curves. Depending on the slope of the curve you can determine whether you are operating in a read noise dominated, shot noise dominated or fixed pattern noise dominated regime. For the E-M5 it appears you have to be in the upper most stop of highlights at base ISO to start to see fixed pattern noise effects become significant. Any lower level of exposure at base ISO or moving to a higher ISO and fixed pattern noise will be mostly masked by shot noise and read noise. You can of course measure FPN even at lower exposure levels if you take multiple exposures and average them - the shot noise and read noise will average away while the fixed pattern noise will remain.

Big snip

bobn2 said:

I think what is particularly interesting is the huge increase in DR. What might be happening is that the E-M5 is capturing texture that is really there in the sky. The sky is full of dust and water vapour, and one wouldn't expect it to be 'flat'. At a short shutter speed, a camera with high DR will capture this, while the eye, with its long integration time, evens it out. However, if you prefer the GF2 result, you can simply replicate it by adding a dollop of noise in post.

--

Bob
'Technology' is a name that we have for stuff that doesn't work yet.
Douglas Adams.

Click to expand...

I had a recent discussion re the potential of rising/dissipating fog contributing to lack of sharpness but didn't consider the capture of texture as being a potential source of "apparent noise". Could this be an example of what you are suggesting:

Original image:



Lack of sharpness and noise in the sky is identified and discussed.

Effects of atmospherics is identified. The next post shows the amount of change in the scene in a few minutes.

Although this doesn't help me with the original question, I find it very helpful with my general education as a photographer.

Many thanks!

--
Tom
The best part of growing old is having the opportunity to do so.

kenw said:

bobn2 said:

OK, I look to your tests with interest.

Click to expand...

Got some access to blue sky today.

All shot with E-M5 at ISO 200 F/5.6. The test cases are:

• 150mm 1/2000 infinity focus
• 15mm 1/2000 infinity focus
• 15mm 1/2000 close focus
• 15mm 1/5 infinity focus with ND400 filter

So to review, we've shot with an order of magnitude difference in angular resolution as well as physical aperture size, we've shot both infinity focus and close focus and because the claim was made that somehow no one has ever noticed "sky texture" with the human eye despite a few centuries of looking through powerful telescopes and binoculars that perhaps the integration time of the eye was an issue we've also shot at a slower shutter speed one about four times the integration time of the light adapted eye.

If the claims of "sky texture" are to have any merit in experiment (as they clearly have none in theory to begin with) then we should see some sort of difference in these sky patches.

All processed in LR with default processing except NR and sharpening turned off.

I'd label them, but as you can see it doesn't matter - they are all the same as we should expect. EXIF info still there if you want to sort them out a bit more. I also took the time to examine these closely directly in LR in case anything might be masked by the export process for uploading. Again, no difference.

I'm putting the "sky texture" theory to rest now. No theoretical basis, no experimental evidence. Doesn't exist. It is clearly the camera and the processing chain.

Click to expand...

Many thanks for taking the trouble to do the test Ken. Although I found the conjecture you rejected extremely implausible from the outset, it is always nice to have the evidence required to say that it is plain wrong.

bobn2 said:

... However, if you prefer the GF2 result, you can simply replicate it by adding a dollop of noise in post.

Click to expand...

I prefer my smog be creamy. Creamy rusty rose or gray orange is fine. I got no use for smog with visible particulates. Too realistic for me :^|

I read through a good chunk of this but hadn't gotten to these sample pictures.

I also appreciate the effort made in taking them.

Sky texture seemed unlikely... but I thought of desserts that look creamy yet have a little texture/grit kinda feel to them. Maybe not a dessert from a fancy restaurant, but dessert still. Just because something can't be seen doesn't mean it can't be detected another way (camera sensor or tongue).

I wondered if the particulates large enough to photograph are the natural kind or the man-made/pollution kind.. A particulate/texture photo could be used to study pollution.

GeorgianBay1939 said:

Big snip

GeorgianBay1939 said:

I think what is particularly interesting is the huge increase in DR. What might be happening is that the E-M5 is capturing texture that is really there in the sky. The sky is full of dust and water vapour, and one wouldn't expect it to be 'flat'. At a short shutter speed, a camera with high DR will capture this, while the eye, with its long integration time, evens it out. However, if you prefer the GF2 result, you can simply replicate it by adding a dollop of noise in post.

--

Bob
'Technology' is a name that we have for stuff that doesn't work yet.
Douglas Adams.

Click to expand...

I had a recent discussion re the potential of rising/dissipating fog contributing to lack of sharpness but didn't consider the capture of texture as being a potential source of "apparent noise". Could this be an example of what you are suggesting:

Original image:



Lack of sharpness and noise in the sky is identified and discussed.

Effects of atmospherics is identified. The next post shows the amount of change in the scene in a few minutes.

Although this doesn't help me with the original question, I find it very helpful with my general education as a photographer.

Many thanks!

Click to expand...

You might see that kenw has done a test which more or less discounts 'atmospherics' as being a general cause of 'sky noise', which doesn't, of course mean that in situations as this photo, with quite big water droplets quite close, it won't give visible 'noise'. Nice photo, by the way.



--
Bob
'Technology' is a name that we have for stuff that doesn't work yet.
Douglas Adams.

GeorgianBay1939 said:

GeorgianBay1939 wrote:
I had a recent discussion re the potential of rising/dissipating fog contributing to lack of sharpness but didn't consider the capture of texture as being a potential source of "apparent noise". Could this be an example of what you are suggesting:

Click to expand...

Dust, water droplets or ice crystals close to the camera can most definitely have a visual impact on an image. And when sunlight is scattered off of them when close to the camera now you can see actual texture or point like sources or texture rather than just a diffuse loss of contrast. The key point though is the particles or droplets in question need to be rather close to the camera and they need to be rather large as well. I've seen photos shot in close to the ground ice fog with low sun where there are obvious glints from scattering/reflections from crystals close to the camera. But for this to happen you have to have particles that are very close to the camera - so as you've shown a good example is standing right in the mist/fog while taking the shot. And usually the actual particles causing any visible glints are much closer to the camera than you'd expect from a casual examination of the final image.

The crux here is that when I've got scattering off of a small particle the "usual" exposure relationships I'm used to with photography do not apply. When we expose typical photographic subjects that are "extended sources" like a rock, house or person the distance to the object does not affect exposure. Furthermore the exposure is determined by the aperture number (e.g. F/5.6). When we expose "point sources" like stars or tiny glints/scatters from small particles the distance to the object does affect exposure and the exposure is determined by the physical aperture size (e.g. F/4 on 100mm lens means 25mm physical aperture).

The effect is even more obvious when shooting with on camera flash. When sunlight is causing the reflections the distance relationship for the brightness of the small glints is square law. The amount of light hitting the particle is independent of the distance from the camera (sunlight is the same everywhere of course). So you just have a square law reduction with the distance of the camera from the reflecting/scattering particle. However, if the light source is from the on camera flash now the amount of light striking the particle does vary with distance from the camera and flash - this is also square law and so the two combine to produce a quartic (fourth power) relationship with distance. As a result an unlucky encounter with a reflecting particle close to the camera when using on camera flash can produce a huge bright artifact. Underwater photographers deal with this all the time since they shoot with strobe a lot and the typical water column has way more and significantly larger particles than air. Taking flash photos in rain or snow produces the same effect.

Lastly the angle of the lighting can make a big difference. Forward scattering (light source directly in front of camera) and back scattering (light source directly behind camera, like an on camera flash) can have significantly higher magnitudes of scattering compared to other angles.

There is one final wrinkle to consider. If I shoot through haze or fog this reduces contrast and saturation. As a result in post processing I'll likely increase contrast and saturation. Doing that of course amplifies sensor noise. That affect is of course nothing to do with any texture in the atmosphere itself and can be easily dealt with by only comparing images with the same post processing.
--
Ken W
See profile for equipment list

bobn2 said:

GeorgianBay1939 said:

Big snip

bobn2 said:

I think what is particularly interesting is the huge increase in DR. What might be happening is that the E-M5 is capturing texture that is really there in the sky. The sky is full of dust and water vapour, and one wouldn't expect it to be 'flat'. At a short shutter speed, a camera with high DR will capture this, while the eye, with its long integration time, evens it out. However, if you prefer the GF2 result, you can simply replicate it by adding a dollop of noise in post.

--

Bob
'Technology' is a name that we have for stuff that doesn't work yet.
Douglas Adams.

Click to expand...

I had a recent discussion re the potential of rising/dissipating fog contributing to lack of sharpness but didn't consider the capture of texture as being a potential source of "apparent noise". Could this be an example of what you are suggesting:

Original image:



Lack of sharpness and noise in the sky is identified and discussed.

Effects of atmospherics is identified. The next post shows the amount of change in the scene in a few minutes.

Although this doesn't help me with the original question, I find it very helpful with my general education as a photographer.

Many thanks!

Click to expand...

You might see that kenw has done a test which more or less discounts 'atmospherics' as being a general cause of 'sky noise', which doesn't, of course mean that in situations as this photo, with quite big water droplets quite close, it won't give visible 'noise'. Nice photo, by the way.

--
Bob
'Technology' is a name that we have for stuff that doesn't work yet.
Douglas Adams.

Click to expand...

Thank you.

Yes, this photo was a bit of a challenge. I wanted to get the diffracted sunlight (both directly and in the iridescent reflection) along with the sparkles in the foreground. I thought that HDR was not really feasible as the skeins of fog were moving surprising quickly. (In retrospect I suspect that using fast burst mode with a bracket might have worked out ok.) In any event it showed the effectiveness of the FZ1000 (Sony 1") sensor and Lightroom sliders!)

I think that KenW gave some really excellent explanations for why we see some "noise" when shooting in fog ... especially in ice fog... which we'll get soon enough. :-(

Thanks a lot.

--
Tom
The best part of growing old is having the opportunity to do so.

kenw said:

kenw said:

GeorgianBay1939 wrote:
I had a recent discussion re the potential of rising/dissipating fog contributing to lack of sharpness but didn't consider the capture of texture as being a potential source of "apparent noise". Could this be an example of what you are suggesting:

Click to expand...

Dust, water droplets or ice crystals close to the camera can most definitely have a visual impact on an image. And when sunlight is scattered off of them when close to the camera now you can see actual texture or point like sources or texture rather than just a diffuse loss of contrast. The key point though is the particles or droplets in question need to be rather close to the camera and they need to be rather large as well. I've seen photos shot in close to the ground ice fog with low sun where there are obvious glints from scattering/reflections from crystals close to the camera. But for this to happen you have to have particles that are very close to the camera - so as you've shown a good example is standing right in the mist/fog while taking the shot. And usually the actual particles causing any visible glints are much closer to the camera than you'd expect from a casual examination of the final image.

Click to expand...

I noticed the phenomena, but didn't really appreciate it last year, when I was shooting landscapes from within low lying radiation ice fog. At the time I was trying to capture snow sparkles caused by specular reflections of an overhead sun with light penetrating the (thin) fog layer to glint off of snow crystals.

kenw said:

The crux here is that when I've got scattering off of a small particle the "usual" exposure relationships I'm used to with photography do not apply. When we expose typical photographic subjects that are "extended sources" like a rock, house or person the distance to the object does not affect exposure. Furthermore the exposure is determined by the aperture number (e.g. F/5.6). When we expose "point sources" like stars or tiny glints/scatters from small particles the distance to the object does affect exposure and the exposure is determined by the physical aperture size (e.g. F/4 on 100mm lens means 25mm physical aperture).

Click to expand...

I have played a LOT* last year trying to capture (specular reflections from snow crystal facets causing) sparkles in the snow. I've tried to get diffraction off of those sparkles from fully stopped down lenses, with "star" filters, with (crappy) software and with severe underexposure. I read that sunlight has a brightness of 34EV(ISO100), compared with bright snow of about 18 EV (ISO100) ... a huge variation in "scene" luminance! The trick seems to be to get bright snow and something obscuring the direct sunlight, then underexposing, pulling down highlights and keeping local and scene contrast up and then playing with so called "Exposure" slider. When you look at the this image at full size you can see the sparkles in the foreground snow. I could see them naked eye, with difficulty in the EVF and I think that I got lucky and was able to capture and bring them out in post processing without making the surrounding snow appear too grey.

kenw said:

The effect is even more obvious when shooting with on camera flash. When sunlight is causing the reflections the distance relationship for the brightness of the small glints is square law. The amount of light hitting the particle is independent of the distance from the camera (sunlight is the same everywhere of course). So you just have a square law reduction with the distance of the camera from the reflecting/scattering particle. However, if the light source is from the on camera flash now the amount of light striking the particle does vary with distance from the camera and flash - this is also square law and so the two combine to produce a quartic (fourth power) relationship with distance. As a result an unlucky encounter with a reflecting particle close to the camera when using on camera flash can produce a huge bright artifact. Underwater photographers deal with this all the time since they shoot with strobe a lot and the typical water column has way more and significantly larger particles than air. Taking flash photos in rain or snow produces the same effect.

Click to expand...

Flash photography is still on my bucket list, but your advice is very useful. Thanks. I just realized that I might be able to get sparkles by using flash and or LEDs at NIGHT or UNDER OVERCAST to reflect sparkles ... at least close in. AHA! Another thing to try!

kenw said:

Lastly the angle of the lighting can make a big difference. Forward scattering (light source directly in front of camera) and back scattering (light source directly behind camera, like an on camera flash) can have significantly higher magnitudes of scattering compared to other angles.

Click to expand...

Right! Similar to specular reflections off of snow crystals which seem to have preferred orientations wrt the sun direction.

kenw said:

There is one final wrinkle to consider. If I shoot through haze or fog this reduces contrast and saturation. As a result in post processing I'll likely increase contrast and saturation. Doing that of course amplifies sensor noise. That affect is of course nothing to do with any texture in the atmosphere itself and can be easily dealt with by only comparing images with the same post processing.

Click to expand...

I don't think that this applied to this particular image. I realize that I probably do that, though, when shooting pix in foggy weather.

kenw said:

--
Ken W
See profile for equipment list

Click to expand...

*LOT of sparkles with various techniques:

http://www.dpreview.com/forums/post/53040315

http://www.dpreview.com/forums/post/53325809

http://www.dpreview.com/forums/post/53363657

http://www.dpreview.com/forums/post/53376078

It is obvious that you have both the physics and photography background to help here. Would you, please?

I need some direction, in addition to learning Photoshop, to get better results here. I suspect that the use of video to convey the "action" of sparkling would help. Another skill still on my "To Learn" list!

Many thanks.

I just read the lengthy discussion of "texture in a blue" sky as being a possible source of "apparent noise". I wish that I read it before making this post . I apologize to the discussants.

Tom

GeorgianBay1939 said:

kenw said:

GeorgianBay1939 said:

GeorgianBay1939 wrote:
I had a recent discussion re the potential of rising/dissipating fog contributing to lack of sharpness but didn't consider the capture of texture as being a potential source of "apparent noise". Could this be an example of what you are suggesting:

Click to expand...

Dust, water droplets or ice crystals close to the camera can most definitely have a visual impact on an image. And when sunlight is scattered off of them when close to the camera now you can see actual texture or point like sources or texture rather than just a diffuse loss of contrast. The key point though is the particles or droplets in question need to be rather close to the camera and they need to be rather large as well. I've seen photos shot in close to the ground ice fog with low sun where there are obvious glints from scattering/reflections from crystals close to the camera. But for this to happen you have to have particles that are very close to the camera - so as you've shown a good example is standing right in the mist/fog while taking the shot. And usually the actual particles causing any visible glints are much closer to the camera than you'd expect from a casual examination of the final image.

Click to expand...

I noticed the phenomena, but didn't really appreciate it last year, when I was shooting landscapes from within low lying radiation ice fog. At the time I was trying to capture snow sparkles caused by specular reflections of an overhead sun with light penetrating the (thin) fog layer to glint off of snow crystals.

GeorgianBay1939 said:

The crux here is that when I've got scattering off of a small particle the "usual" exposure relationships I'm used to with photography do not apply. When we expose typical photographic subjects that are "extended sources" like a rock, house or person the distance to the object does not affect exposure. Furthermore the exposure is determined by the aperture number (e.g. F/5.6). When we expose "point sources" like stars or tiny glints/scatters from small particles the distance to the object does affect exposure and the exposure is determined by the physical aperture size (e.g. F/4 on 100mm lens means 25mm physical aperture).

Click to expand...

I have played a LOT* last year trying to capture (specular reflections from snow crystal facets causing) sparkles in the snow. I've tried to get diffraction off of those sparkles from fully stopped down lenses, with "star" filters, with (crappy) software and with severe underexposure. I read that sunlight has a brightness of 34EV(ISO100), compared with bright snow of about 18 EV (ISO100) ... a huge variation in "scene" luminance! The trick seems to be to get bright snow and something obscuring the direct sunlight, then underexposing, pulling down highlights and keeping local and scene contrast up and then playing with so called "Exposure" slider. When you look at the this image at full size you can see the sparkles in the foreground snow. I could see them naked eye, with difficulty in the EVF and I think that I got lucky and was able to capture and bring them out in post processing without making the surrounding snow appear too grey.

GeorgianBay1939 said:

The effect is even more obvious when shooting with on camera flash. When sunlight is causing the reflections the distance relationship for the brightness of the small glints is square law. The amount of light hitting the particle is independent of the distance from the camera (sunlight is the same everywhere of course). So you just have a square law reduction with the distance of the camera from the reflecting/scattering particle. However, if the light source is from the on camera flash now the amount of light striking the particle does vary with distance from the camera and flash - this is also square law and so the two combine to produce a quartic (fourth power) relationship with distance. As a result an unlucky encounter with a reflecting particle close to the camera when using on camera flash can produce a huge bright artifact. Underwater photographers deal with this all the time since they shoot with strobe a lot and the typical water column has way more and significantly larger particles than air. Taking flash photos in rain or snow produces the same effect.

Click to expand...

Flash photography is still on my bucket list, but your advice is very useful. Thanks. I just realized that I might be able to get sparkles by using flash and or LEDs at NIGHT or UNDER OVERCAST to reflect sparkles ... at least close in. AHA! Another thing to try!

GeorgianBay1939 said:

Lastly the angle of the lighting can make a big difference. Forward scattering (light source directly in front of camera) and back scattering (light source directly behind camera, like an on camera flash) can have significantly higher magnitudes of scattering compared to other angles.

Click to expand...

Right! Similar to specular reflections off of snow crystals which seem to have preferred orientations wrt the sun direction.

GeorgianBay1939 said:

There is one final wrinkle to consider. If I shoot through haze or fog this reduces contrast and saturation. As a result in post processing I'll likely increase contrast and saturation. Doing that of course amplifies sensor noise. That affect is of course nothing to do with any texture in the atmosphere itself and can be easily dealt with by only comparing images with the same post processing.

Click to expand...

I don't think that this applied to this particular image. I realize that I probably do that, though, when shooting pix in foggy weather.

GeorgianBay1939 said:

--
Ken W
See profile for equipment list

Click to expand...

*LOT of sparkles with various techniques:

http://www.dpreview.com/forums/post/53040315

http://www.dpreview.com/forums/post/53325809

http://www.dpreview.com/forums/post/53363657

http://www.dpreview.com/forums/post/53376078

It is obvious that you have both the physics and photography background to help here. Would you, please?

I need some direction, in addition to learning Photoshop, to get better results here. I suspect that the use of video to convey the "action" of sparkling would help. Another skill still on my "To Learn" list!

Many thanks.

--
Tom
The best part of growing old is having the opportunity to do so.

PS I hope that I am not derailing the OP's thread. If so, I could start yet ANOTHER thread dealing with sparkles!!

t

Click to expand...

GeorgianBay1939 said:

I have played a LOT* last year trying to capture (specular reflections from snow crystal facets causing) sparkles in the snow. I've tried to get diffraction off of those sparkles from fully stopped down lenses, with "star" filters, with (crappy) software and with severe underexposure. I read that sunlight has a brightness of 34EV(ISO100), compared with bright snow of about 18 EV (ISO100) ... a huge variation in "scene" luminance! The trick seems to be to get bright snow and something obscuring the direct sunlight, then underexposing, pulling down highlights and keeping local and scene contrast up and then playing with so called "Exposure" slider. When you look at the this image at full size you can see the sparkles in the foreground snow. I could see them naked eye, with difficulty in the EVF and I think that I got lucky and was able to capture and bring them out in post processing without making the surrounding snow appear too grey.

Click to expand...

That sounds like the most sensible approach to me as well. As I alluded to before there is the possibility that these snow sparkles are going to act like point sources and so physical aperture size rather than aperture number may control their exposure. So going to some what longer focal lengths may improve their contrast over the background snow.

GeorgianBay1939 said:

*LOT of sparkles with various techniques:

http://www.dpreview.com/forums/post/53040315

http://www.dpreview.com/forums/post/53325809

http://www.dpreview.com/forums/post/53363657

http://www.dpreview.com/forums/post/53376078

It is obvious that you have both the physics and photography background to help here. Would you, please?

I need some direction, in addition to learning Photoshop, to get better results here. I suspect that the use of video to convey the "action" of sparkling would help. Another skill still on my "To Learn" list!

Click to expand...

Those are some really interesting posts! I'm only on the forum in bits and bursts these days and wasn't visiting back when you posted those. Thanks for the pointers!

My initial thoughts and suggestions would be:

• As mentioned if these truly act as point sources then in theory "zooming in" at the same aperture number should increase the contrast ratio. By that I mean shooting a longer focal length from the same spot (don't back up when using the longer focal length). That would be an interesting experiment.
• You mention video for the "action" of sparkling which I interpret to mean the sparkles vary with time. That would imply there is a balance to be struck in exposure time. If your shutter speed matches the length of time of the sparkle (or is shorter) you'll get the maximum contrast for the sparkle. On the other hand, if the sparkles are infrequent then the shorter your exposure time the fewer sparkles you will capture in a given image. Your current exposures appear to be in the 1/1000 range already and you are definitely capturing sparkles. If you haven't already an interesting experiment in "sparkling conditions" would be to try a range of equivalent exposures with different apertures/shutter speeds. You might learn something about the how the contrast ratio of the particles and their frequency vary with shutter and aperture if for instance you shot 1/1000 F/11 and 1/8000 F/4. Of course with a star filter this probably gets complicated as the star filter effect varies with aperture.
• If the sparkles vary with time and you just want more sparkles in a given photo then take many exposures and combine them with a maximum filter. So lets say you have the same scene shot from a tripod and in ten exposures there are sparkles all in different parts of the scene. In PS you could blend all ten images using the mixing mode that always takes the brightest pixel of the ten images. You'll get ten times as many sparkles in the final image as you would in a single image.
• Try a polarizer to improve contrast ratio. Since this is water ice (i.e. dielectric) and not a metal the reflections may be polarized. We are used to thinking of using a polarizer to eliminate reflections but you can also use it to increase the contrast of a reflection by orienting it 90 degrees away from the "eliminate" orientation. So you might first experiment to see if you can use a polarizer to block the sparkles. If that works then rotate the polarizer a quarter turn from where it eliminates them and you should see about a stop or two of improved contrast compared to no polarizer.

Looks like you've got a good photography project to occupy yourself in the winter months! Brrrrr!

P.S. The swirly stuff in your one shot that you suspect is from the star filter is pretty wild. Never seen that before, but like you I suspect the star filter is the culprit though I don't have any good explanation as to why.
--
Ken W
See profile for equipment list

GeorgianBay1939 said:

I have played a LOT* last year trying to capture (specular reflections from snow crystal facets causing) sparkles in the snow.

Click to expand...

Your post reminded me of some snow sparkles I shot in March 2013 on a rather cold day. The main difference: The sparkles I could see came in about all rainbow colors. When in focus they looked very tiny, but in the out-of-focus areas they were quite nice! Two unedited original files, Oly 520, the first one with the kit lens 40-150, the second one with a 180/2.8 manual Nikkor.









And two crops from the upper part of the second one. No idea what I did to the first one, lol, I just wanted to see what it looks like if the snow was black! :-D In the second one I think we can see the nine aperture blades of the Nikkor lens:









René

kenw said:

GeorgianBay1939 said:

I have played a LOT* last year trying to capture (specular reflections from snow crystal facets causing) sparkles in the snow. I've tried to get diffraction off of those sparkles from fully stopped down lenses, with "star" filters, with (crappy) software and with severe underexposure. I read that sunlight has a brightness of 34EV(ISO100), compared with bright snow of about 18 EV (ISO100) ... a huge variation in "scene" luminance! The trick seems to be to get bright snow and something obscuring the direct sunlight, then underexposing, pulling down highlights and keeping local and scene contrast up and then playing with so called "Exposure" slider. When you look at the this image at full size you can see the sparkles in the foreground snow. I could see them naked eye, with difficulty in the EVF and I think that I got lucky and was able to capture and bring them out in post processing without making the surrounding snow appear too grey.

Click to expand...

That sounds like the most sensible approach to me as well. As I alluded to before there is the possibility that these snow sparkles are going to act like point sources and so physical aperture size rather than aperture number may control their exposure. So going to some what longer focal lengths may improve their contrast over the background snow.

kenw said:

*LOT of sparkles with various techniques:

http://www.dpreview.com/forums/post/53040315

http://www.dpreview.com/forums/post/53325809

http://www.dpreview.com/forums/post/53363657

http://www.dpreview.com/forums/post/53376078

It is obvious that you have both the physics and photography background to help here. Would you, please?

I need some direction, in addition to learning Photoshop, to get better results here. I suspect that the use of video to convey the "action" of sparkling would help. Another skill still on my "To Learn" list!

Click to expand...

Those are some really interesting posts! I'm only on the forum in bits and bursts these days and wasn't visiting back when you posted those. Thanks for the pointers!

My initial thoughts and suggestions would be:

• As mentioned if these truly act as point sources then in theory "zooming in" at the same aperture number should increase the contrast ratio. By that I mean shooting a longer focal length from the same spot (don't back up when using the longer focal length). That would be an interesting experiment.

Click to expand...

Thanks, I'll try that.

kenw said:

• You mention video for the "action" of sparkling which I interpret to mean the sparkles vary with time. That would imply there is a balance to be struck in exposure time. If your shutter speed matches the length of time of the sparkle (or is shorter) you'll get the maximum contrast for the sparkle. On the other hand, if the sparkles are infrequent then the shorter your exposure time the fewer sparkles you will capture in a given image. Your current exposures appear to be in the 1/1000 range already and you are definitely capturing sparkles. If you haven't already an interesting experiment in "sparkling conditions" would be to try a range of equivalent exposures with different apertures/shutter speeds. You might learn something about the how the contrast ratio of the particles and their frequency vary with shutter and aperture if for instance you shot 1/1000 F/11 and 1/8000 F/4. Of course with a star filter this probably gets complicated as the star filter effect varies with aperture.

Click to expand...

I should clarify. When walking or driving by or even moving my head, I see different facets reflecting very briefly, since the xtal facets behave like very small plane mirrors with varying orientations wrt the Sun. That very brief capture of bright light by my eyes adds to the experience ... almost like distributed scintillation. So I was thinking of shooting some video this winter just to capture the experience and maybe share it on UTube or some site like that. Frame captures would not be significant, methinks.

But that is a good experiment. I had not tried that before.

kenw said:

• If the sparkles vary with time and you just want more sparkles in a given photo then take many exposures and combine them with a maximum filter. So lets say you have the same scene shot from a tripod and in ten exposures there are sparkles all in different parts of the scene. In PS you could blend all ten images using the mixing mode that always takes the brightest pixel of the ten images. You'll get ten times as many sparkles in the final image as you would in a single image.

Click to expand...

They would only vary over a significant time period as the sun moves. Another good idea.

kenw said:

• Try a polarizer to improve contrast ratio. Since this is water ice (i.e. dielectric) and not a metal the reflections may be polarized. We are used to thinking of using a polarizer to eliminate reflections but you can also use it to increase the contrast of a reflection by orienting it 90 degrees away from the "eliminate" orientation. So you might first experiment to see if you can use a polarizer to block the sparkles. If that works then rotate the polarizer a quarter turn from where it eliminates them and you should see about a stop or two of improved contrast compared to no polarizer.

Click to expand...

Actually, I'd try the the polarizer to DECREASE contrast ratio, preventing oversaturation of the specular reflections. ( The difference in brightness of the sparkle with the surrounding snow is about 16 stops on a clear day!)* If I could stop the sparkles down several stops I would be able to keep them small instead of blobs.

* I remember doing a calculation last year where I found that the EV(ISO100) of the sun, when viewed directly is about EV= 34 (ISO 100).

kenw said:

Looks like you've got a good photography project to occupy yourself in the winter months! Brrrrr!

Click to expand...

Yes, a good challenge. Fortunately I shoot most of this stuff from the comfort of the cab of the truck, on the back roads.

kenw said:

P.S. The swirly stuff in your one shot that you suspect is from the star filter is pretty wild. Never seen that before, but like you I suspect the star filter is the culprit though I don't have any good explanation as to why.

Click to expand...

Yes, this one:

http://2.static.img-dpreview.com/files/p/E~forums/53365904/f6de7dd4a21e4c79a619cc304aa029a5

Strange, eh? I will try to replicate it this winter!!!

kenw said:

--
Ken W
See profile for equipment list

Click to expand...

Many thanks for your help!

René Schuster said:

GeorgianBay1939 said:

I have played a LOT* last year trying to capture (specular reflections from snow crystal facets causing) sparkles in the snow.

Click to expand...

Your post reminded me of some snow sparkles I shot in March 2013 on a rather cold day. The main difference: The sparkles I could see came in about all rainbow colors. When in focus they looked very tiny, but in the out-of-focus areas they were quite nice! Two unedited original files, Oly 520, the first one with the kit lens 40-150, the second one with a 180/2.8 manual Nikkor.

And two crops from the upper part of the second one. No idea what I did to the first one, lol, I just wanted to see what it looks like if the snow was black! :-D In the second one I think we can see the nine aperture blades of the Nikkor lens:

René

Click to expand...

Those are fantastic! Slightly Out Of Focus specular reflections of sunlight specular reflections showing bokeh, I think. I cannot explain the difference in colours, although I do remember getting several like that last winter. Here is a strange one caused by the diffraction off of the star filter (We think.)

http://2.static.img-dpreview.com/files/p/E~forums/53365904/f6de7dd4a21e4c79a619cc304aa029a5

--
Tom
The best part of growing old is having the opportunity to do so.

Fantastic images! I think that the colors must come from some refraction phenomena going on in the snow flakes, like in minute prisms. But as the snow flakes are not aligned, we don't see a rainbow effect.

Very nice!