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The Human Eye

Intro

The human eye is an amazing thing. For decades now, we’ve been trying to emulate the human eye with camera technology, but we’re nowhere close to being even nearly as good. I recently received a Quora request to write about what the specifications of the human eye would be as a camera. Unfortunately, no one really read it, but I learned so much while researching that I thought I should share it here. I had to remove a lot of the actual math from my Quora answer, but I am going to put it here as a form of documentation.

Parameters

So, what are the important parameters to consider here?

  • Resolution: How much detail can the human eye perceive?

  • Focal Length: What is the focal length of the human eye, and how does it change?

  • Shutter Speed: How fast can the human eye perceive things?

  • Aperture: What is the range of f/stop values that the eye can achieve?

  • Dynamic Range: How much difference in light can the human eye see?

Resolution

imiIn order to figure out resolution, we must first talk about visual acuity. Visual acuity is the spatial resolution of the visual processing system, and measures the clarity of vision. This clarity of vision determines the human eye's ability to percieve details, a factor that should be taken into consideration when talking about resolution.

The first way we can talk about resolution is by simply adding the number of data points within the human eye. The human eye has two types of photoreceptors; rods and cones. Rods mostly deal with low light vision, and lack colour sensitivity. The cones are less sensitive to light than the rods, but they are able to detect colour. There are about 120 million rods in the average person's eye, and approximately 6-7 million cones. The colour information of the cones is combined with the light information from the rods. This is similar to the way that older black and white photographs would be taken with coloured filters, then projected with those same filters to make a full colour image. By adding the number of rods and cones together, we get a value of about 126-127 million data points in the eye. This would be equivalent to about 126.5 million pixels, or 126.5 megapixels.

However, this doesn't take into account visual acuity. Let's look at a worst case scenario; in 0.34 lux (an amount of light approximately equal to the light put out by the full moon on a clear night) the human eye has a visual acuity of 1.7. For reference, a visual acuity of 0.1 on the decimal scale would qualify as being legally blind, and a visual acuity of 1.6 would represent the limit of a normal range of vision right before ranging into the realm of visual impairment.

A visual acuity of 1.7 when taking a Snellen test (the test when you go to the eye doctor) represents a value of 0.59 arc-minutes per line. Two pixels per line pair are needed to see any object that isn't a point, so this returns a value of 0.259 arc-minutes per pixel. The number of pixels/data points that the human eye is able to see is calculated by taking this value, then figuring out the arc-minutes per degree. The number of degrees the human eye can see is respresented by our Field Of View (FOV), which is about 120 by 120 degrees.

This allows us to calculate the resolution from the following equation: Horizontal FOV x Vertical FOV x (arc-minutes/(arcminutes/line)) 2 . When the relevant values are substitued into the equation, it gives us 120 x 120 x (60/0.3) 2 .

The final output of the equation is 576,000,000 data points, which is approximately equal to 576 megapixels. However, we have to account for loss of FOV from hair, nose, overlap, eyelashes, etc. It's safe to say that the average person's eyes will have a resolution of about 360 megapixels. This value isn't exactly representative of the resolution of the human eye, since we rarely utilize all of the data points simultaneuously to give that incredible resolution.

Just how incredible is that resolution? Well, watch this video:

This video shows an initial image with a resolution of 560 megapixels, and zooms in on a 12 megapixel crop of this image. This would be the same as being able to utilize the full resolution of the eye to detect the minor details in any image.

Focal Length

This may not be the first thing you think about when you hear about the eye, but it is very important. This impacts the aperture of our eyes, and is one of the most hotly debated topics when considering how the human eye compares to a camera. It’s a commonly stated fun fact that the human eye is similar in focal length to a 50mm lens. However, that is quite untrue. The field of view of the human eye, including peripheral vision, is about 120 degrees. This would make it equivalent to about a 10mm lens on a full frame camera. However, this is different from the actual image focal length of the eye.

The image focal length of the eye is the distance from the back of the lens inside the eye to the retina. Now, the image focal length is what we need to consider here, rather than the object focal length, because the focal length of a camera lens only measures image focal length. This distance is measured using this equation:

so represents the distance from the eye to the object. si represents the distance from the back of the lens to the retina when the lens is pulled taught (approximately 24mm). n i represents the refractive index of the liquid inside the eye (approximately 1.33). fi represents the image focal length of the eye.

At infinity focus, the equation simplifies out to fi = si. When focusing at infinity focus, the lens is pulled taught because it doesn't need to distort the light rays to cause them to converge. As such, the focal length is equal to 24mm.

At close focus, the focal length differs on a person by person basis. Adults can only focus at about 25cm away from their eyes. By substituting the values into the equation (so = 250, ni = 1.33, and si = 24), we get the final result of fi = 22.4mm - However, this result is only for adults. Children's eyes can focus as close as 6.5 centimetres. When we work out the equation, this time substituting 65 for so, we get the final result of fi = 18.8mm.

To summarise, the focal length of the average adult’s eyes is about 22-24mm. The focal length of children’s eyes can be as large as 19-24mm. The field of view is approximately 120 degrees by 120 degrees including peripheral vision, which makes the human eye similar to a 10mm lens on a full frame camera body.

Aperture

Aperture is the opening inside the camera lens that allows in the light. The direct equivalent to this in the human eye would be our pupils. A wider aperture results in a brighter picture and the opposite is true for a narrow aperture, just like the dilation and constriction of our pupils. Aperture is ususally measured in 'f-stops', which help us figure out the aperture range of the human eye. F stops are measured by dividing the lens' focal length by a number, for example - f/1, f/1.4, f/2, f/2.8, etc. Since the diameter of the entrance pupil differs on a lens by lens basis, aperture is denoted by the divisor of the focal length. The equation to measure the aperture is:

N represents the aperture setting, L represents the focal length of the lens, and D represents the diameter of the opening that allows light into the lens.

According to a study carried out by the National Center for Biotechnology Information (a part of the US National Library of Medicine), adult's pupil size ranges from 2-4 mm when constricted, to 4-8mm when dilated. This gives us theoretical minimum and maximum widths of 2mm and 8mm respectively.

When these are substituted into the equation, the resultant f/stop range is f/2.75 to f/12. However, when children's ability to focus on close objects is taken into account, we can achieve a maximum aperture of f/2.35.

One important thing to note is that f/stop isn't directly proportional to the t/stop value. The light transmittence is rarely less than the f/stop, but is usually quite similar. This was just to establish details of the human eye in terms we can all understand.

Shutter Speed

The optic nerve in the eye is made up of axons which then turn into a bundle of nerves that form the optic nerve, which is then myelinated. Unmyelinated nerves fire anywhere from 0.5m/s to 15m/s. However, since the optic nerve is myelinated, it can theoretically travel at speeds of up to 150m/s. Additionally, the nerves in the eye are shown to be able to fire up to 300-1000 times per second. However, that is purely theoretical.

In practice, people are not able to perceive differences from one 1000th of a second and the next. People can typically see changes from one 1/150th of a second and the next. However, people can perceive an image that only exists for 1/220th of a second. The issue here is not the eye’s ability to see the images, but the ability to see any changes in between them. It’s similar to using a 1/1000th shutter speed while filming a video at a lower frame rate- The camera can have a much higher shutter speed, but the gaps in between each exposure aren’t filled with any data.

As such, people can really only comprehend images that exist for 1/220th of a second or longer. However, this varies on a person-by-person basis. It is also possible to train your perception- some E-sports gamers have trained their perception so that they can use 240Hz monitors to make sure they can see changes and react to them as fast as possible.

Dynamic Range

The dynamic range of the eye changes depending on scene (more on this later), which makes it hard to have any definitive value that represents it. However, it is somewhat easy for people to calculate the dynamic range of their own eye in a more practical sense.

Dynamic range is measured in stops, where each stop represents twice the amount of light of the previous stop, calculated like so: Light * 2 number of stops. A simple test of this can be looking at a bright object, then looking at a dark one. People often measure their dynamic range by looking at stars, because they vary wildly in stellar magnitude. You can compare the luminance of the faintest and brightest star you can see to find out the dynamic range.

Theorectically, the human eye is able to see a luminance range of 1014:1. When we put this value into the equation log2(100,000,000,000,000), the result is approximately 46.5 stops. This, therefore, is the theoretical dynamic range of the human eye. However, the human eye cannot percieve this data at all points in time.

The rods inside the eye have a dynamic range of about 20 stops. However, the rods are able to increase and decrease their sensitivity to light in order to view brighter or darker objects. The majority of this change can occur in as little as 4 seconds, but the full adaptation of the rods to the dark takes considerably longer (this is influenced by a myriad of factors including blood flow, retinal health, etc.).

However, the static dynamic range of the human eye is about 30 stops- this is the range that the human eye can see 100% of the time, and as such is the best way to measure the dynamic range of the human eye in a majority of circumstances.

Summary

This exercise was quite interesting, as it incorporates physics, biology, and photography into an exercise that’s easy to understand. The goal of many photographers is to make their photos look realistic, and document the scene as the eye would have scene it. However, the capability of the human eye is very different from that of any camera, so it is best to go for a more artistic choice.

Who knows? Maybe in a few decades we’ll be able to surpass the capabilities of the human eye with our own technology. Until then, we’ll be striving to achieve the same level of quality.

Ankit KumarComment
Why Mirrorless?

In my previous post, I mentioned that I had switched from a DSLR to a mirrorless camera. In this post, I'm going to walk you through my reasoning for doing so.

In June, I switched from Canon's crop sensor DSLRs to a Sony a7riii. There are a few main considerations that influenced my choice to do so:

  • More Compact and Lighter

  • Full Frame Format

  • Adapting From 3rd Party Lenses

  • Future-Proofing

More Compact and Lighter

When you live in a country like Singapore, it's perfectly normal to get the travel bug. Exploring new places is always something to look forward to. When I started photography, carrying one camera body and one lens was easy enough to stuff into a bag, or just keep on hand. As I started experiencing the well known phenomenon of GAS (Gear Acquisition Syndrome), it started to get more difficult to travel with all the camera equipment I wanted to. 

Then came the advent of the mirrorless camera. It had been around for a while now, but it was finally accepted as a proper tool rather than a gimmick. The smaller body allowed my to fit more stuff into a camera bag than every before. Furthermore, the light weight allowed me to lug around more equipment. Some of you will note that mirrorless lenses are longer than DSLR lenses, as you can't disobey the rules of optics. However, my main struggle was packing the large DSLR body, which was an awkwardly thick and tall shape. The lenses can simply be placed vertically to maximise space.

Full Frame Format

My previous camera bodies were all crop sensor cameras. For those of you who don't know, crop sensor cameras have a smaller image sensor. This has a few major effects:

  • Typically better Dynamic Range

  • Typically better low light performance

  • Better Depth Of Field when using equivalent focal lengths and the same aperture


Obviously, a full frame camera has very different applications than a crop sensor camera. What drew me to this mirrorless system was that I could get a full frame mirrorless that was smaller than my crop sensor DSLR. Even if I didn't switch to a mirrorless camera, I was planning to eventually transition to a full frame system. The Sony packed so many features into one body, that it made more sense to jump ship from Canon to Sony in order to get them.

Adapting 3rd Party Lenses

Sony themselves said that it was possible for the end user to adapt lenses to their system. This is a great feature of practically all Mirrorless cameras: the short flange distance allows you to add back some distance to adapt lenses. This meant that I could still use my Canon lenses on my Sony body.

However, the autofocus performance was sufficiently bad that I transferred to Sony's own glass. The reason I am still interested in adapting is that Sony is still building up its lens selection over time. Since I can adapt other, very specialised, lenses, I have a greater lens selection than any single DSLR company can offer.

Future Proofing

The switch to a mirrorless market is inevitable. It may not be in five year, or even ten years. But I am sure that it will happen eventually. By switching now, I can benefit from the innovation that mirrorless bodies are incorporating now. Some of these amazing new features are:

  • Pixel-Shift: This shifts the sensor 4 times to gain much more RGB data per pixel than any single photo can hope to. This, in theory, increases detail, and colour reproduction.

  • Electrical Viewfinder: Now that I've used this, I can't imagine going back to a regular Optical Viewfinder. The electrical viewfinder can simulate the final image that will be produced, it can zoom to aid with manual focus whilst also providing peaking, and it can display the full menus and settings that the camera is using.

  • Augmented Video Recording: Now, this is not necessarily exclusive to mirrorless cameras, but some of the best still+video Interchangeable Lens Cameras are mirrorless cameras (Fuji xt-3, Sony a7sII, etc.). The fact that the cameras have the ability to oversample the footage to reproduce cleaner colours and detail is a big sell for people who want to take videos and photos in tandem.


Maybe some of these innovations will make their way to DSLRs over time, but they are available on mirrorless systems now, which allows me to be ahead of the curve. Additionally, DSLR giants Canon and Nikon have recently released their first attempts at a mirrorless system.

Conclusion

So, this is a whole lot more information than one of my posts typically contains, and it completely lacks any pictures. However, I felt that this would be interesting to explain why I would make such a drastic switch, and maybe even help some of you readers learn a bit more about Mirrorless ILCs.

Ankit KumarComment
Changes

Well, It’s Been a While

Its been really long since I last updated this blog, and a lot's happened since then. What follows is a quick run down in some of the major changes that have happened regarding my photography.

  1. I was twice highly honoured by Nature's Best Photography Asia (and you can see those photos and the description on their site here: http://www.naturesbestphotography.asia/en/gallery/) 

  2. I have taken the plunge, and switched to a mirrorless. This obviously represents a big change, and there will be an upcoming post on why I chose to do so. Suffice it to say, there were significant benefits provided by the mirrorless system that I didn't have on my DSLR.

  3. I have diversified my portfolio even more; I've done more videos, and I've been doing a lot of print work

Videos?

I'm glad you asked! A lot of people these days understand that videos are simply a sequence of pictures. However, the way that one edits the photos is very different from videos. I've had to undergo a lot of learning in order to learn how to make videos the way that I do. I enjoy using Adobe Premiere, as it doesn't have a very steep learning curve. Some things are very similar though, such as exposure controls and Lumetri colour. 

I mostly do timelapse videos, as it allows me to maintain a lot of control over my camera. Before I actually start to understand shooting video, taking photos and them stitching them into videos is a nice way to bridge the two. You can find a lot of my timelapse videos on my instagram (@Ankitohmatix), and there'll be some more in depth posts about said videos. In the meantime, check out the videos below:

Prints

In this age of digital photography, it is quite easy to share your photos over the internet, and quickly send it to someone. The portability of keeping a picture on your phone to share it with others is so convenient!

However, there is a certain satisfaction that can only be achieved through seeing your photos in print. The ability to see your work in a physical form provides some unique characteristics. The light bouncing off of the deep colours makes it look much nicer than . simple screen could ever hope to.

I produced a series of prints to help support my charity that I run (you can visit us at www.wayto.help, or by clicking the button below). At first, we managed to coordinate with a local restaurant that agreed to host a gallery evening. Afterwards, the photos hung in the Singapore American Club for two months. 

This lead me to create my own page for prints! You can visit it by clicking the button below, or by visiting the Prints page on this website. The store is quite new, and will continue to be updated with more photos that you can buy. There are a variety of mediums on offer, and if you enjoyed the photos on this site or my blog, it is a great way to have a nice little keepsake, or even a gift now that the season of giving is approaching!

Ankit KumarComment
Lunar Eclipse

In my post about my photography in Singapore, I said that I was going to attempt to take some photos of the lunar eclipse on January 31. When I got my stuff all ready to go, the weather didn't look promising to say the least: rain pouring down, the occasional flash of thunder. Not the best weather to be lugging around a massive lens and a tripod. Just as the sun was setting, I had lost hope. I had already gone to spot that I had planned before, but the rain wasn't letting up. However, I was lucky enough to already be at the right spot when the rain stopped, which meant that I didn't have to waste any time getting set up. This allowed me to make the mosaic of all the phases of the eclipse that you can see below:

I also wanted to capture the moon rising above the skyline. Unfortunately, due to error in my planning, I overshot by a bit. Despite that, I still managed to capture the following video of the moon rising over the Singapore Flyer:

Anyway, that's all for my eclipse. I really hope that you enjoyed this post, and I hope you come back to see what new content I have! 

Ankit KumarComment
Singapore Skyline

I used to never take photos in Singapore. All that I used to think Singapore photos were  just portrait and street shots. One day, I saw a beautiful intro to a youtube video taken from the waterfront in the Singaporean CBD. That gave me the idea to take a photo from the CBD; however, I didn't want to just copy someone else. I flew my drone as high as I thought safe (it was a windy day), and stitched together my photos to make a massive photo:

After I had taken the photos that I would then turn into a panorama, I brought the drone back to the ground, and switched out the batteries before taking off again once the sun had fully set. When there was no sunlight, and the water reflected the lights from the skyscrapers, it looked absolutely beautiful. When I got home, I combined several shots together to reduce the shakiness of the pictures, to create the following photo:

In the future, I'm really looking forward to photographing the upcoming lunar eclipse from Singapore, and I will post my results on here!

Ankit KumarComment
Underwater Photography

What’s so great about it?

Well, being underwater is special itself; whenever I go diving, that weightless feeling and the unique surroundings are completely wonderful things to experience in your life time. It's so amazing that mankind has managed to find a way to search the endless oceans, and see a whole other world.

So, how are the photos?

When I started diving, I saw the raw, natural beauty of the ocean. I saw sharks lazily gliding through the water, moray eels poking their heads out of crevices, turtles propelling themselves through the water with the current and giant schools of fish diving and swarming in a horde. I wanted to be able to capture what I saw, and show others the real beauty of the ocean. 

 The first time I used the camera, I was doing my PADI Sea Turtle Awareness Speciality. This meant that I had to catch up to turtles, and take a photo of the side of their face. Fun Fact: the side of a turtle's face has a unique pattern that can be used to identify that individual, like a fingerprint. I dove under the waves, and spent a day looking for turtles and photographing them. Most of the turtles were hawksbill, and had very dirty shells. I was beginning to lose hope of seeing a green turtle: the type of turtle with a beautiful, patterned shell. Then, as I had only 70 PSI remaining in my tank (50 PSI means that you are low on air, and you have to surface ASAP), this green turtle appeared from behind us, and allowed me to take this shot before carrying on into the infinite blue. We then surfaced, and headed home for the day.

The next day, we travelled to a different dive site, one which was famed for how many different types of fish coexisted in one area. As soon as I dived down, I noticed the large amounts of anemones. Then, I noticed this little guy, curiously looking at me, and I decided to snap a picture. The reason why clownfish live in anemones is because they are immune to the sting from several species of anemones, and they can be protected from predators. 

Then, I went swimming along the reef, with the current. I stopped for a second, and then this school of yellow fusiliers swam around me, creating a tunnel effect. It was truly a great experience to see all these fish slowly swimming around me while I floated in place. 

After seeing that, I continued along the reef. Then, I felt a tapping on my shoulder. I turned around, and my dive buddy pointed at a fever of eagle rays that were travelling up the reef. Eagle rays are generally very shy creatures, and the fact that they let me swim close enough to them to take this photo was very special. I watched them slowly glide away, and over the reef. We then had to surface, and go back.

That was my last dive there, and they I headed home the next day.

Would I do it again?

In a heartbeat! It was so amazing to see these beautiful sights, experience the majesty and wonderful setting that the ocean provides. More than that, diving was very calming, and I never wanted to leave the water. If I get another chance to do it again soon, I'll take the chance over almost anything else, hands down.

Ankit KumarComment