Digital IR

[tuco]

Very nice Tuco! I like the tonality and sharpness of that image.

Thanks Jon.

[jon.oman]

A few shots from today. All shot with the 950nm filter.



2021:09:03 12:52:11 : NIKON D810 : 24mm : 100 ISO : F7.1 : 1.3 sec : 5/3 EV



2021:09:03 12:39:38 : NIKON D810 : 29mm : 100 ISO : F7.1 : 1.6 sec : 5/3 EV



2021:09:03 13:03:19 : NIKON D810 : 28mm : 100 ISO : F7.1 : 0.8 sec : 5/3 EV

I used a tripod for all of these shots. There is some movement of the leaves. I guess I need to bump up the ISO.

These were shot at a local Summerville park. It is actually inside of town, surrounded by buildings.

[Audii-Dudii]

I used a tripod for all of these shots. There is some movement of the leaves. I guess I need to bump up the ISO.

FYI, increasing the ISO will clip the highlights by a corresponding amount because the sensor's full-well capacity is fixed and it can count only so many photons before it reaches its design limit and is not able to count any additional photons beyond that. On the positive side, with some sensors, increasing the ISO will also result in less noisy shadows, offsetting some (but not all) of the dynamic range that is lost when ISO is increased.

For better and worse, however, your D810's sensor is not one of those sensors and increasing ISO offers very little net improvement in shadow performance to offset the unavoidable loss of dynamic range that occurs when increasing the ISO setting. If you actually need to use all the dynamic range your sensor can record when photographing a scene, then increasing the ISO will result in reduced image quality because the highlights will be clipped and any detail that would have been recorded but for being clipped has been lost. (Although the technical explanation for why this is so can be difficult to understand, this chart summarizes the net effect for your D810: https://www.photonstophotos.net/Char...m#Nikon%20D810)

In short, when faced with a situation such as the one you experienced, your best bet's to simply change the shutter speed to whatever speed is necessary to prevent motion blur of the leaves and then increase the exposure during post-processing to compensate for the fact that less light was captured during the exposure instead of increasing ISO. As a rule, the only time you should ever increase ISO above your D810's base ISO setting is when you have no alternative because you can't see the scene well enough in the viewfinder to compose and focus your photo ... seriously!

Personally, I find this to be especially true when I'm photographing in IR, because I'm usually doing so in the middle of the day, when the sunlight is at its peak and the contrast ratio of scenes is at its highest, so I need the sensor to record as much detail as possible to maximize image quality. (This is the reason why I usually capture seven identical files, even when I'm photographing handheld, then median-blend them into a single-file as the first step in my post-processing workflow. Because the reduction in shadow noise not only maximizes image quality by minimizing any clipping of the highlights, but allows me more flexibility when tone-mapping the file into its formal, final version.)

Of course, on overcast days or when photographing lower contrast scenes, clipping highlights is less likely to occur, in which case you may be able to get away with increasing ISO if you need to do so to better see the scene you're photographing without also suffering a corresponding reduction in dynamic range.

(As an aside, all of the above also holds true when photographing at night using long exposures, which is how I finally came to understand that increasing ISO over the base setting is to be avoided whenever possible. Because it's very rarely helpful and almost always detrimental with regard to image quality. When people ask me how I'm able to achieve the results I do with my nighttime photography, I remind them that just as there's no replacement for displacement when racing cars, there's no replacement for capturing as much light as possible, ceteris paribus, which can only happen when camera is set to its base ISO.)

Oh and nice photos! 8^)

[jon.oman]

In short, when faced with a situation such as the one you experienced, your best bet's to simply change the shutter speed to whatever speed is necessary to prevent motion blur of the leaves and then increase the exposure during post-processing to compensate for the fact that less light was captured during the exposure instead of increasing ISO. As a rule, the only time you should ever increase ISO above your D810's base ISO setting is when you have no alternative because you can't see the scene well enough in the viewfinder to compose and focus your photo ... seriously!

(This is the reason why I usually capture seven identical files, even when I'm photographing handheld, then median-blend them into a single-file as the first step in my post-processing workflow. Because the reduction in shadow noise not only maximizes image quality, but allows me more flexibility when tone-mapping the file into its formal, final version.)

So, if I understand you correctly, for the image with the park bench, I should go into manual mode and expose the scene at f7.1 for 1/10th of a second to prevent the leaves from blurring (basically underexposing the scene). Then in post-processing I should correct the exposure to bring it back to normal. This way I get the best of both worlds. Also, If I shoot the scene seven times, and median-blend them, I will regain any quality I may have lost by doing this manipulation.

[alanbutler57]

Pecos National Monument several years ago. D70 plus deep red (opaque) filter.

[Audii-Dudii]

So, if I understand you correctly, for the image with the park bench, I should go into manual mode and expose the scene at f7.1 for 1/10th of a second to prevent the leaves from blurring (basically underexposing the scene). Then in post-processing I should correct the exposure to bring it back to normal. This way I get the best of both worlds. Also, If I shoot the scene seven times, and median-blend them, I will regain any quality I may have lost by doing this manipulation.

Yes and No.

With your D810, leaving ISO alone and setting the shutter speed to whatever it needs to be to eliminate any blurring of the leaves will achieve the maximum dynamic range (hence maximum image quality) possible with no blurred leaves visible.

Depending on how important it is to you to eliminate blurred leaves, this may or may not represent the ultimate image quality possible, period, as there are other factors in play here, too.

But Yes, if your goal is to achieve the maximize image quality while also eliminating blurred leaves, then underexposing the scene to prevent clipping the highlights and correcting the exposure during post-processing to restore the highlights to their original brightness, is the only way to achieve it.

I may not have been as clear about this in my post as I could have been, but my point is that increasing ISO should always be the last resort, not the first resort, because there's a price to be paid in terms of image quality whenever the camera -- in this case, your D810 -- is set to anything but its base ISO. (This may not be true for other cameras, mind you, but it is true for your D810 and my A7R.)

As for median-blending, assuming the files to be blended are identical (or as close to identical as possible), you won't just recover any image quality you may have lost, you will actually achieve more / better image quality than you could have achieved using a single exposure! Because the process of doing this reduces the noise level of the blended file by the square root of the number of exposures that were median-blended into a single file. For seven files, this works out to an improvement in the SNR of 2.65 dB; for nine files, the improvement is 3 dB, and for 15 files, it's 3.9 dB! (Note: When median-blending files instead of, say, mean blending (i.e., averaging) them, you should always blend an odd number of files. Because when an even number of files are median-blended, the software doing the blending has to calculate the mean value of each pixel by averaging the values on either side of it, which is potentially less accurate than simply selecting the median value directly.)

By reducing the overall noise level of the file, you are increasing the SNR (effectively the same as Dynamic Range), which provides you with more flexibility both pre- and post-exposure. For example, when you know the shadow areas will be less noisy after median-blending, you also know you can more aggressively tease details from them in post-processing, so you can further reduce the exposure and hold even more detail in the highlights by further reducing any clipping, all without negatively affecting the shadow areas. Alternatively, you can leave the highlights alone and recover more detail from the deepest, darkest shadow areas without also increasing the visible noise artifacts.

Of course, everything is a compromise, so if the wind is blowing heavily and you don't want the final file to include any motion blur, then median-blending shouldn't be used and you need to set the initial exposure accordingly. (That said, if you always capture seven files, you don't necessarily have to make this decision at the time of the exposure, since you can always select just one of the seven files later and process that. And so you know, the reason I use seven files instead of another number is this is how many files my NX500 will capture before the buffer kicks in and the exposure rate slows down. This provides me with an audible cue as to when I have captured seven files so I don't need to keep track of the count and I know exactly when I no longer need to hold the camera as steady as possible. This number may be higher or lower with other cameras, so you'll have to experiment to determine the best number of files to capture for your purposes.)

Take this photo, for example:



Without median-blending seven files into one, there's no way I would have been able to hold detail in the sunlit parts of the white stucco and reveal detail in the shaded parts of the brown stucco when photographing with my NX500. Although the sensor in the NX500 performs remarkably well for its age -- even today, six years after it was released, there are very few other APS-C sensors that can match its performance, let alone best it! -- its smaller sensor fundamentally limits its dynamic range to roughly a stop less than what my A7R can achieve. (In fact, the NX500's sensor actually outperforms the A7R's sensor on a pixel-level basis, but this isn't enough to overcome the A7R sensor's advantage of being a larger size and having more pixels.)

Anyway, you'll ultimately need to experiment with this technique yourself to determine whether any of what I've covered above is useful for you and the type of photography you do. Fortunately, the only cost to do so is time, so there isn't much downside to at least checking out and seeing for yourself the results that are possible... 8^)

[sanking]

I may not have been as clear about this in my post as I could have been, but my point is that increasing ISO should always be the last resort, not the first resort, because there's a price to be paid in terms of image quality whenever the camera -- in this case, your D810 -- is set to anything but its base ISO. (This may not be true for other cameras, mind you, but it is true for your D810 and my A7R.)

In general I agree with your point, but in a specific condition where leaves moving because of wind is concerned the only way to improve the situation is to increase ISO to the point where the shutter speed freezes movement. Then in Camera Raw adjust to decrease noise as best you can.

Sandy

[Greg]

Presently shoot with a Nikon Z6 converted to shoot IR. Usually I shoot three bracket images (+ & - 2 or more f stops) in RAW. Handheld no problem. PhotoMatix Pro 6 easily aligns them. Resulting image file contains a lot of information that I am able to manipulate and tweak in PS. FYI: 24-70 Z lens works fine. 24-200 Z lens produces a hot spot so delegated to conventional color photography.

[Audii-Dudii]

In general I agree with your point, but in a specific condition where leaves moving because of wind is concerned the only way to improve the situation is to increase ISO to the point where the shutter speed freezes movement. Then in Camera Raw adjust to decrease noise as best you can.

Sandy:

You can increase the shutter speed to the same point where the shutter speed freezes movement without also increasing the ISO setting.

And then correct for the resulting underexposure in Camera Raw instead of reducing the amount of noise that results when using your approach.

If you do this with a D810, you should find this approach achieves better quality results than the approach you outlined. Note: This may or may not be true for other cameras as well, but it definitely is true for D810 and my A7R.

Because the key to eliminating the motion blur is increasing the shutter speed, not increasing the ISO setting. The ISO setting merely adjusts the gain of the electronics processing the electronic signal created by the sensor and has nothing whatsoever to do with the exposure; i.e., the amount of light recorded by the sensor.

Test this with your camera and report back with the results.

[sanking]

Sandy:

You can increase the shutter speed to the same point where the shutter speed freezes movement without also increasing the ISO setting.

And then correct for the resulting underexposure in Camera Raw instead of reducing the amount of noise that results when using your approach.

If you do this with a D810, you should find this approach achieves better quality results than the approach you outlined. Note: This may or may not be true for other cameras as well, but it definitely is true for D810 and my A7R.

Because the key to eliminating the motion blur is increasing the shutter speed, not increasing the ISO setting. The ISO setting merely adjusts the gain of the electronics processing the electronic signal created by the sensor and has nothing whatsoever to do with the exposure; i.e., the amount of light recorded by the sensor.

Test this with your camera and report back with the results.

Interesting point, and with very low signal strength I am sure you are right. I have from time to time experienced a condition in photographing in nature in areas where there was no artificial light late in the evening when the gain in IR sensitivity around the time of sunset went from fair to non-existent in an instant.


Sandy