Featured Articles and Reviews

Wildlife Photography Tips Part Two

It has taken a little longer than I wanted, but I finally got around to writing this second article on photographing wildlife. The writer in me is … [Continue Reading]

600lb Wet Black Bear

Fuji X-T1 Review

This is an in-depth review of the Fujifilm X-T1, a weather-proof mirrorless interchangeable-lens camera from Fuji that was announced on January 28, … [Continue Reading]

Fuji X-T1

How to Photograph Clouds

Nature often rewards us with incredible opportunities for photographing sunrises, sunsets and sun rays piercing through the clouds, creating stunning … [Continue Reading]

Mt Rainier Sunset

Tamron 150-600mm f/5-6.3 Review

This is a detailed review of the Tamron SP 150-600mm f/5-6.3 Di VC USD, an ultra-telephoto zoom lens that was announced in November of 2013 for … [Continue Reading]

Tamron 150-600mm f/5-6.3 Di VC USD

Apple Mac Pro Review for Photography Needs

I never thought that I would be reviewing an Apple Mac Pro, since I have never owned a Mac and was always a PC user. In fact, the last time I really … [Continue Reading]

Apple Mac Pro

How to Photograph Cathedrals

I have been fortunate enough to see some truly spectacular cathedrals in my time, particularly in Europe, and even here in the United Kingdom we are … [Continue Reading]

St Alban's Cathedral

Why Downsampling an Image Reduces Noise

One of our readers, Mike Baker, sent the below email to me today. I thought it was a great and interesting analysis of why downsampling an an image reduces noise, so I decided to share it with you (with his permission, of course). Trying to digest this stuff makes my head spin, but it is a great read. You might need to read it several times to understand what he means, especially with all the mathematical formulas (I had to):

You recently commented about downsizing a high-resolution image to a lower-resolution in order to reduce the apparent noise. While I knew that this is an effective way to reduce noise visible in the images, I had not thought in much detail about the technical reasons why this works.

After a long evening’s thought on the subject, and running a few questions past my friend and fellow engineer, I believe I have a (reasonable, though perhaps not perfect!) handle on the subject…

If the image signal and the image noise had similar properties, averaging neighboring pixels in order to reduce the resolution would not improve the signal-to-noise ratio. However, signal and noise have different properties.

There is (in general) no relationship between the noise in neighboring pixels. Technical junkies call this “no correlation”.

Correlation is the long-term average of the product of two signals N1 x N2. If two signals have no correlation, then the mean of their product is zero.

The signal in neighboring pixels has a high degree of correlation. If you add uncorrelated signals, then their “power” is added, meaning the combined signal is the square root of the combined power.

N_comb = sqrt(N1^2+N2^2) and for N1 = N2 = N we get N_comb = sqrt(2)*N, where N1, N2 are root-mean-square (RMS) values of the noise.

However, if signals are highly correlated, then their sum is effectively the sum of their magnitudes:

S_comb = S1+S2 and for S1=S2=S we get S_comb = 2*S

So, if we add the content of two neighboring pixels, we get:

SNR_comb = S_comb/N_comb = sqrt(2)*(S/N)

So, the signal-to-noise increases by square root of two, which is about 40%.

Now, you may say that the signal in neighboring pixels is not always 100% correlated. The correlation between the signals depends on the image content. If the image content is very smooth, the correlation is high. If the image content varies very fast, the correlation is low. Of course, noise will be more noticeable in smooth areas and the effect of resampling the image will be stronger.

Adaptive noise filters take into account the absolute signal-to-noise and the image content. They reduce the resolution more in areas that are smooth and have poor signal-to-noise and keep the original resolution in areas that have strongly varying image content and high signal-to-noise. You can think of it as a joint optimization of SNR and resolution.

Now, we also need to look into the different sources of noise:

  1. The first source of noise is dark current which is caused by electrons that accumulate in the individual pixel well, even if there are no photons entering (lens cover on). Dark current becomes dominant for very long exposures. For normal exposures the errors from trapped electrons are negligible.
  2. The second source of noise is the read-out noise. This is essentially generated by two sources: A) Noise added by the amplifier and B) Noise generated by the analog-to-digital converter. It is a fixed amount of noise that is added to each image during read-out. When you choose the ISO setting on your camera, you essentially set the read-out gain and therefore the read-out noise. The higher the ISO, the higher the read-out gain and the less read-out noise. Of course if you pick an ISO which is too high you will get signal saturation. So for low-light situations always pick an ISO that is no higher than needed to capture the image you want.
  3. The third source of noise is called “quantization noise” and is a bit harder to understand. It has to do with the fact that (in low-light conditions) we don’t sample a smooth, continuous flow of photons but rather discrete bunches of photons. The problem is, that a source of light does not produce a stream of photons that are spaced equally in time. So, if you image a low light source that sends out (on average) 100 photons per second, you may receive 90 photons for the first second, 105 for the second etc.. The average error will be on the order of the square-root of the number of photons (or electrons in the pixel sensor well). A typical sensor well contains between 20,000 and 60,000 electrons when fully charged. The maximum amount depends on the pixel size. A sensor well with 20,000 electrons has an error of approx +/-141 electrons when fully charged or +/-0.7%. A well with 60,000 electrons has an error of approx +/-245 electrons when fully charged or +/-0.4%. While we may be able to reduce dark current and read-out noise by cooling the sensor, there is essentially nothing we can do about it. If we keep on shrinking the pixels, we will have smaller and smaller electron wells and less and less electrons trapped.

    The above errors of 0.7% or 0.4% appear rather small and we would not be able to notice them. However, in low-light situations, sensor wells will be only partially filled. If we only manage to trap 1000 electrons, the error becomes 3%. If we only trap 100 electrons, the error becomes 10%.

    Notice that the term “quantization noise” has nothing to do with the signal quantization by the analog-to-digital converter. It has to do with the fact that your signal actually arrives in quantums of energy.

What do you guys think? Anyone wants to challenge Mike’s analysis? :)

Nikon 85mm f/1.8G is available for pre-order at B&H

I have also been notified that the brand new Nikon 85mm f/1.8G is also available for pre-orders at B&H, shipping around the same time as D4, which is mid-February. As always, I highly recommend B&H for their superb service and lowest prices.

Nikon 85mm f/1.8G Preorder at B&H

Nikon D4 is available for pre-order at B&H

I have just been just notified that B&H is now accepting pre-orders for the Nikon D4, with shipping to start around mid-February. As always, I highly recommend B&H for their superb service and lowest prices.

Nikon D4 Preorder at B&H

Here is the link: Nikon D4 at B&H ($5,999)

Benefits of a High Resolution Sensor

As camera manufacturers are continuing the megapixel race, with Sony releasing a bunch of 24 MP APS-C (1.5 crop-factor) cameras like Sony A77, A65 and NEX-7, and Nikon releasing a high resolution 36 MP Nikon D800, many of us photographers question the need for such a high resolution sensor. Some of us are happy while others are angry about these latest trends. Just when we thought companies like Nikon abandoned the megapixel race, instead of seeing other companies do the same, we now see Nikon back in the game with a new breed of product with a boatload of pixels. Why did Nikon all of a sudden decide to flip the game? Why does everyone seem to be going for more pixels rather than better low-light / high ISO performance? Does a high resolution sensor make sense? What are the true benefits of a high resolution sensor? In this article, I will provide my thoughts on what I think has happened with Nikon’s camera strategy, along with a few points on benefits of a high resolution sensor.

Nikon D4 Sensor

Pixel Size, Pixel Density, Sensor Size and Image Processing Pipeline

OK, this topic is rather complex if you do not know anything about pixels and sensors. Before you read any further, I highly recommend to read my “FX vs DX” article, where I specifically talk about pixel and sensor sizes and their impact on image quality.

[Read more...]

Nikon D4 vs D800

While the Nikon D800 has not officially been released yet, its specifications have been leaked for a while now, so our readers have been asking more and more questions about it. In this Nikon D4 vs D800 comparison, I will write about the rumored specifications of the D800 and compare it to the Nikon D4. While these cameras are for completely different needs and obviously are at difference price points, both are generating lots of interest from the Nikon community. Once the Nikon D800 is officially released and I have both cameras, I will provide much more detailed analysis of differences between these cameras, along with image samples and ISO comparisons. Please keep in mind that some of the D800 specifications below are pure speculation and might not match the actual specifications of the camera when it is released.

Nikon D4 vs D800

Before I get into the camera specifications comparison, let me first talk about these two cameras. The Nikon D4 is a high-end DSLR targeted at news, sports, wildlife and action photographers. It is Nikon’s new flagship low-light king with very impressive high ISO capabilities and extremely fast speed, both in terms of autofocus and camera frame rate. To allow for such impressive low-light performance, Nikon had to keep the pixel size large, which translates to lower resolution (by lower I mean 16.2 MP). The upcoming Nikon D800, on the other hand, is aimed at landscape, architecture and fashion photographers that need high resolution for large prints.

[Read more...]

Nikon D4 vs D3s

Many of the current Nikon D3s owners like me probably wonder about the differences between the new Nikon D4 and the now obsolete Nikon D3s DSLR cameras. While I do not yet have the Nikon D4 to do more in-depth side by side comparisons, I decided to write about differences in body design and specifications between the two. More details about the Nikon D4 will be published in my upcoming Nikon D4 review.

Nikon D4 vs D3s

First, let’s talk about differences in camera body design.

Nikon D4 vs D3s Camera Body Design Comparison

As expected, the Nikon D4 went through rather significant changes in camera body design. The overall shape of the camera has been completely changed and it now looks more curved than the D3/D3s/D3x models. Let’s start from the front of the camera, which went through the least number of changes. The only major change I see on the front is the C/S/M focus lever (bottom left side of the camera) that has been modified to adapt to the same switch we see on the Nikon D7000 DSLR. This was a good design change, because it will prevent accidental changes to autofocus when you pull the camera out of the bag. Now the switch only has two options – AF for autofocus and M for manual focus. The button on top of the switch replaces the AF mode switch on the back of the camera. Now you can switch between the different AF modes (single, dynamic and 3D) by pressing this button and rotating the camera dial. Oh and it looks like the grip is shaped a little differently, which should help with handling the camera a little more.

[Read more...]

Nikon 85mm f/1.8G Announcement

Along with the Nikon D4, Nikon also announced the AF-S Nikkor 85mm f/1.8G lens today. While all photography sites are buried with the Nikon D4 announcement, this little gem is receiving very little attention. I am super excited about this portrait lens, because it not only replaces the old 85mm f/1.8D, but considering how good the latest f/1.8 lenses have been, should deliver superb performance at a relatively low price of $500.

Nikon 85mm f/1.8G

You might be wondering why one would want an 85mm lens, if there are cheaper 50mm portrait lenses out there. Well, 50mm lenses were never considered to be portrait lenses in the past, because 50mm falls into the “standard” range. However, because of digital cameras with smaller cropped sensors, 50mm lenses are now more like 75mm lenses, which is too long for a standard range and hence the new name. Even I often refer to the 50mm lens as a “portrait” lens. In fact, 50mm lenses are not portrait lenses – they are just designed to be small, lightweight and portable for everyday photography and occasional portraiture. 85mm lenses, on the other hand, are specialized tools created specifically for portraiture in mind. This means that they are optically designed to deliver outstanding results when photographing people with very sharp optics, superb colors and exceptionally good-looking bokeh. The current Nikon 85mm f/1.4G, like its predecessors, is often called the “bokeh king” for a reason – there are very few lenses out there that can deliver similar results (the superb Nikon 135mm f/2.0 DC is one of them).

[Read more...]

Nikon D4 DSLR Announcement

Nikon has just released the much anticipated Nikon D4 DSLR, a major update to the existing Nikon D3s camera that was released back in 2009. The Nikon D4 is Nikon’s flagship DSLR, designed specifically for sports, news, wildlife and event photography that require superb low-light capabilities. Due to the high resolution sensor of the Nikon D800, we might not see a Nikon D4x for landscape and fashion photography needs, but a Nikon D4s might follow in a couple of years.

Nikon D4

So, what does the Nikon D4 bring to the table? Here is a summary of its features:

  1. Sensor: 16.2 MP FX, 7.3µ pixel size
  2. Native ISO Sensitivity: 100-12,800
  3. Boost Low ISO Sensitivity: 50
  4. Boost High ISO Sensitivity: 25,600-204,800
  5. Camera Buffer: Up to 100 12-bit RAW images, 70 14-bit uncompressed RAW and up to 200 JPEG images in continuous 10 FPS mode with XQD card
  6. Processor: EXPEED 3
  7. Dust Reduction: Yes
  8. Shutter: Up to 1/8000 and 30 sec exposure, self-diagnostic shutter monitor
  9. Shutter Durability: 400,000 cycles
  10. Camera Lag: 0.012 seconds
  11. Storage: 1x Compact Flash slot and 1x XQD slot
  12. Viewfinder Coverage: 100%
  13. Speed: 10 FPS, 11 FPS with AE/AF locked
  14. Exposure Meter: 91,000 pixel RGB sensor
  15. Autofocus System: Advanced Multi-CAM 3500FX with 51 focus points and 15 cross-type sensors
  16. AF Detection: Up to f/8 with 11 focus points (5 in the center, 3 on the left and right)
  17. LCD Screen: 3.2 inch diagonal with 921,000 dots
  18. Movie Modes: Full 1080p HD @ 30 fps max
  19. Movie Exposure Control: Full
  20. Movie Recording Limit: 30 minutes @ 30p, 20 minutes @ 24p
  21. Movie Output: MOV, Compressed and Uncompressed
  22. Two Live View Modes: One for photography and one for videography
  23. Camera Editing: Lots of in-camera editing options with HDR capabilities
  24. Wired LAN: Built-in Gigabit RJ-45 LAN port
  25. WiFi: Not built-in, requires WT-5a and older wireless transmitters
  26. GPS: Not built-in, requires GP-1 GPS unit
  27. Battery Type: EN-EL18
  28. Battery Life: 2,600 shots
  29. Weight: 1,180g

[Read more...]

What is Moiré?

Moiré pattern occurs when a scene or an object that is being photographed contains repetitive details (such as lines, dots, etc) that exceed the sensor resolution. As a result, the camera produces a strange-looking wavy pattern as seen below:

Moiré

(Image courtesy of photo.net)

See how noticeable the moiré pattern is on the jacket? That’s moiré for you, at its worst. Moiré is almost never seen in nature, but is very common in everyday objects and items around us – you might see it in all kinds of fabric, straight hair, architecture, etc. You might have even seen it on your television. In photography, moiré happens mostly because of the way light reaches the sensor and how the sensor interprets the light through the bayer interpolation filter.

While there are methods to effectively reduce moiré, there is no easy way to completely remove it in post-processing software. Lightroom 4 will ship with a moiré reduction tool and Nikon will also ship its next version of Capture NX with built-in moiré reduction functionality, but neither one will be able to fully get rid of the worst moiré pattern occurrences.

Here is a comparison between the Nikon D800 and D800E (the latter is prone to moire), which clearly shows Moiré on the Nikon D800E (Image courtesy of Nikon):
Nikon D800 vs D800E Moire

See “How to Avoid Moiré

What is a Low-Pass Filter?

A low-pass filter, also known as anti-aliasing or “blur” filter, was designed by camera manufacturers to eliminate the problem of moiré by blurring what actually reaches the sensor. While extreme details are lost in the process, the problem of moiré is completely resolved. Since most cameras are designed to be used for day-to-day photography, where moiré pattern is very common, most cameras on the market today use a low-pass / anti-aliasing filter. While this surely benefits most photographers out there, it is a big blow on landscape photographers that never see moiré and yet end up with blurred details. Because of this problem, some companies on the market started specializing in removing the low-pass / anti-aliasing filter from modern DSLR cameras, specifically targeting landscape photographers. Most digital medium-format and some high-end cameras do not have a low-pass filter, because they want to deliver the best performance from their sensors. While those cameras are affected by moiré, manufacturers leave it up to the photographer to decide on how to avoid it or deal with it in post-processing. Below you will find two examples of low-pass filters used on typical Nikon DSLRs and on the Nikon D800E.

A typical low-pass filter contains of 3 or more different layers, as shown on the top illustration below:

Nikon D800 vs D800E Low-Pass Filter

As light rays reach the first “horizontal low-pass filter”, they get split in two, horizontally. Next, they go through an infrared absorption filter (illustrated in green color). After that, the light rays go through the “second vertical low-pass filter”, which further splits the light rays vertically. This light ray conversion process essentially causes blurring of the details.

With the Nikon D800E DLSR model, Nikon took a different approach. The full low-pass filter cannot be completely removed, because it would cause the focal plane to move; plus, the camera still needs to be able to reflect infrared light rays. Instead of making a single filter with one layer, Nikon decided to still use three layers, but with two layers canceling each other out. As light rays get split into two with a vertical low-pass filter, then through the IR absorption filter, those same light rays get converged back when passing through a reversed vertical low-pass filter. Hence, instead of getting blurred details as in the first illustration, we get the full resolution.

I am not sure if the above method is the best way to deal with the issue, but I suspect that Nikon decided to take this route for cost reasons. It would probably be more expensive to produce a single IR absorption filter layer coated on both sides, than continue to use the same layers, but in a different configuration.

Here is a sharpness comparison between the Nikon D800 and D800E (Image courtesy of Nikon):
Nikon D800 vs D800E Sharpness