Sense and Sensor-bility

While I was looking things up for my post about how I ended up with the Canon Rebel T6 and my lens trifecta, I also got sucked into finding out about camera specifications, which led to camera sensors. Turns out it was a bit of a rabbit hole.

To start, digital camera sensors are the equivalent of film in analog cameras. They capture light and record color to reproduce images. Older digital cameras often used CCD (charge coupled device) sensors, but they’ve since been replaced by CMOS (complementary metal oxide semiconductor) sensors. Both types of sensors rely on photosensitive semiconductors that convert light into electric charge. The charge is then converted into voltage, and the correlation between light (brightness) and voltage can be used to recreate the photograph. CCD sensors are analog devices that send the charges from each semiconductor through an output node to be transformed into voltage while CMOS sensors convert charge to voltage at each individual pixel. While CCD sensors were originally the sensor of choice because of their low noise, CMOS sensors are cheaper and require less power, and technological advances have improved image quality to equal or better CCD sensors.

For color photography, a color filter array sits on top of the sensor. Commonly used in digital cameras today is the Bayer filter, which contains RBG color filters arranged in a checkerboard-like pattern on the pixel array of a sensor. The Bayer filter has 50% green filters, 25% red filters, and 25% blue filters, which reflects the physiology of the human eye. Because each pixel now only sees either red, blue, or green, the image needs to be processed with a demosaicing algorithm to give each pixel RBG values. For example, a green pixel has its green value measured directly, then can get its red and blue values by interpolating from its red and blue neighbors.

At the library
[Samsung Galaxy J3 Orbit, 3 mm, f/1.9, 1/40 s, ISO-125]

Finally, on to sensor size. In filmmaking and film photography, 35 mm film was the most commonly used film size, so when digital cameras became a thing, a sensor size that matched 35 mm film – 36mm x 24mm – became known as “full frame.” In general, bigger sensors/film require bigger lenses/cameras that are more expensive, so camera manufacturers also came out with so-called “crop sensor” or “APS-C” cameras with sensors typically sized at 22.3mm x 14.9mm (Canon) or 23.5mm x 15.6mm (every other brand). Then there’s the Micro Four Thirds System, 1-inch sensors, and once you get smaller than that (as in a lot of point and shoot/phone cameras), sensor size is usually expressed as something like 1/2.3”. This number ostensibly refers to the diagonal of the sensor, but it’s based on old video camera tubes, which were sized based on outer diameter, not usable inside area, so a 1/2.3” (0.435”) sensor actually has a diagonal of around 0.3” and dimensions of 0.24” x 0.18” (6.17mm x 4.55mm).

Argo Park on the Border to Border
[Fujifilm FinePix XP55, 7 mm, f/4.3, 1/58 s, ISO-100] 

Once you have your sensor, you then divide it into thousands of areas that each correspond to a pixel. The bigger a pixel is, the more light it individually captures, and the better it can capture whatever you’re photographing. For example, the Fujifilm FinePix XP55 has a 1/2.3” sensor and a resolution of 4320 x 3240 so has a pixel size of about 1.4 microns on a side (6.17 mm/4320 = 1.4 microns). My Rebel has the Canon APS-C sensor and a resolution of 5184 x 3456, giving a pixel size of ~4.3 microns. So even though the megapixels aren’t that different (4320 x 3240 = 14 million pixels, or 14 megapixels vs. 5184 x 3456 = 18 MP), the larger sensor and pixel sizes mean improved picture quality.

Tree at sunset
[Canon Rebel T6, 55 mm, f/8, 1/160 s, ISO-100]

Out of interest, I tabulated the specifications for a number of cameras I’ve owned below. The top of the table (click to enlarge) is digital cameras and the bottom is phone cameras. For fun I included Canon’s current most expensive professional mirrorless camera, the R5, which at $3899 for the body alone I don’t anticipate owning any time soon, if ever (I’ll be holding out for a mirrorless crop sensor R-mount camera for when I need to replace my T6; the current APS-C mirrorless line uses a different lens mount with few native lenses and like Canon’s entire range of DSLRs and lenses, seems to be a developmental dead end.). I also put in Apple’s latest and greatest offering, the iPhone 13 Pro, for comparison with my phone, which cost about the same as a pair of Airpods.

I was surprised by a few things, and unsurprised by others. First, I didn’t realize that my DSLR didn’t have many more megapixels than the FinePix XP55 or even the PowerShot SD1300. The sensor size, however, is over 11 times larger in area, and jumping up to a full frame sensor, though it doesn’t look massively larger, still more than doubles sensor area. On the flipside of things, I think I’m justified in my dislike for my phone camera, which at best has a sensor less than half the size of a 16-year-old digital camera. And even though one of the most advanced iPhones has surpassed my more recent point and shoots in sensor size, that sensor is still less than a sixth of the size of my entry level DSLR’s, which is one reason why people still pay hundreds and thousands of dollars for DSLRs and mirrorless cameras.

¹My phone camera (unsurprisingly?) not only has microscopic sensors, but also non-standard size sensors, so the inch equivalent is approximated from the sensor dimensions.

²I couldn’t find the aspect ratio for the iPhone’s sensor, but it’s stated to be a 1/1.65” sensor, so those are the approximate sensor dimensions and resolution based on a 4:3 aspect ratio and the given megapixels. Calculations are for the iPhone’s best (largest sensor/most megapixels) camera.

Project Recap [misty mountains]

The latest big project I completed was for no one in particular. I liked the pattern when I saw it, it was on sale, and it didn’t require too many colors, so I ended up picking up the thread for it when I went shopping for the supplies for my previous two projects (the monarch butterfly and sunset lake).

The (untitled) pattern was drafted by ZephyrMood and I purchased it on Etsy. There were ten colors, with only one color needing more than 1 skein if stitching on 14 count aida with two strands. It was a full coverage pattern, all full cross stitches with no backstitching or specialty stitches. Not a whole lot of confetti stitching to speak of, and enough color blocks to mostly work tree by tree at the bottom and by horizontal layers in the mountains.

Fog on mountains and trees

The circular pattern measures 112 x 112 stitches, or 8 inches in diameter on 14 count fabric. My unwashed project measures about 8 1/16” wide and 7 7/8” high, so slightly off like all my other projects, but not noticeably uncircular. Based on the area of a circle, the stitch count is somewhere north of 9800 stitches, though the sum of the given stitch counts for each color in the pattern is 9715. I started right after Christmas and finished a few days after Valentine’s Day, for a total elapsed time of 55 days, an average of ~180 stitches per day, though I didn’t work on the project every day. At this time in real life, it was after I defended, then before/after my final thesis submission, when my brain appreciated taking a break from micelles and margin formatting. I currently don’t have the supplies for my next project, so I’ve turned to the library to start going through Terry Pratchett’s works and RNG-ing my way though a long list of sci-fi and fantasy titles.

This pattern was based on a watercolor work by another Etsy seller, AquarelleSpace. One of the problems with some of the pattern mills that have popped up is that when they make patterns by running photos and artwork through pattern generating software, the resulting patterns can sometimes be not great, with excessive confetti and random colors with two or three stitches in the entire pattern. That was not the case here, and I thought it was a good adaptation of the original watercolor. The only negative was that there’s no stitched model on the Etsy page, so the colors in the mockup don’t exactly match the floss colors in real life, but I still think the finished project turned out well. I worked off the 1 page tablet pdf version of the pattern, with the symbols over colored squares. Symbol choices were reasonable and the pattern was easy enough to read. Overall, a solid pattern, I like the final result, and even the top however many stitches done entirely in 3865 weren’t too bad with a YouTube video or podcast running in the background.

Winter

After returning from the Upper Peninsula, as I mentioned in my yearly post, I jumped into speed writing my thesis before defending right before Christmas, then final thesis revisions were due in January. In between all that, I generally carried on as usual with life in Ann Arbor. It wasn’t a particularly cold or snowy winter, so I got outside when I could, including biking through the winter months. Right after Thanksgiving, I got my telephoto zoom lens, so I also spent time crawling through the undergrowth looking for squirrels and birds.

Squirrel

Early in December, I paid a visit to the arboretum to try out my telephoto lens. Around that same time, the public golf courses run by Ann Arbor Parks and Rec open up to walkers/dog walkers/etc. by inverse rule – from March to November, non-golfers are explicitly not allowed to be on the golf course, but if it’s not March to November, they’re not not allowed. I’ve mostly been walking in the same circles for the past two and a half years, so the golf course is a nice variation and it gives the golf course purpose in the winter.

Golf course cloud at sunset

I also continued on my other usual paths. The ornaments were out again this year in one of the parks I frequent, and I found some new additions. The week before Christmas, Ann Arbor got freezing rain, and I made a loop around my neighborhood to get photos. Between Christmas and New Year’s, a coworker and I made a trip to the botanical garden when the weather was too nice to stay inside. The indoor conservatory had reopened by then, and had a couple Christmas trees plus an “art” exhibit where they put frames around some of their plants to highlight different design principles used in art like color, space, texture, etc.

Some sort of Christmas rodent

Christmas tree at the botanical garden conservatory

With my bike in action and a telephoto lens in hand, I headed to the Huron River a couple times in January because from prior years I knew that a lot of ducks/geese/swans gather along the shores of the Huron during winter. It was mostly mallards and Canada geese, but also some trumpeter swans and once I saw a pair of hooded mergansers. With the weather holding through January, I biked my new telephoto lens out to the Barton Nature Area as well, but arrived in time for the sun to be setting directly over the river, so didn’t get a whole lot with it.

Barton Dam

February finally stayed cold enough any snow we got to stick around for a while. One day, we were getting a good amount of soft, fluffy snow, the kind that sticks to branches if there’s not too much wind, so after work I headed out with my camera. Mid-February, there was one warm day that I took my bike out on the Border to Border trail. The B2B, at least the sections that go through the major parks, does get snow removal services during the winter, so that was clear. Once I got to the Parker Mill Park section, it was slushy, but passable with my all-purpose Target children’s bicycle. Then I got a look at the Matthaei Botanical Gardens Trail, and somewhere in the back of my mind I think I did remember it falls into the university’s “no winter maintenance” category. The MBGT was essentially melted water over hard packed snow/ice, in other words, very slippery. At that point I decided it was not a good day to die, so I turned back there.

Snow on trees

Near, Far, Wherever You Are

I originally started the previous post to talk about my new camera lenses, but spent too much time going on about how I ended up with the Canon Rebel T6 over one of the dozens of other cameras out there so I split the post up to talk about the body and lenses separately. So here’s the post I meant to write to show off some photos from my telephoto lens (since my ultra wide-angle lens was already featured in my Acadia and Upper Peninsula posts).

When I got the T6, it came bundled with a kit lens – the EF-S 18-55mm f/3.5-5.6 IS II.¹ If you mostly want a DSLR for snapshots of everyday life and travel, the kit lens is great. If you’re using an entry level DSLR to dip your toe into photography, it’s still good, especially for a kit lens, but you’ll eventually want a lens upgrade. I ended up shooting with the 18-55mm only for three and a half years, but then bought not one, but two lenses within six months of each other.

One of the things that you actually often lose out on when you first get a DSLR is zoom. While point and shoot cameras and phones can use digital zoom and other tricks to increase focal length, there are physical limitations to whatever lens you have on a DSLR. I like the T6 kit lens, and it’s chosen as the kit lens because it covers a useful range of focal lengths similar to what the human eye sees, but it’s not the sharpest, and I wanted to take pictures of squirrels and other things and have them appear larger than my thumbnail on my computer screen.

Mallard duck [250 mm, f/8, 1/160 s, ISO-1600]

However, I first picked up an ultra wide-angle lens over a telephoto lens because I was about to head to Acadia with my family and I figured I’d rather get better image quality for landscapes on that trip. Based on quality and price, Canon’s EF-S 10-18mm f/4.5-5.6 IS STM³ lens is more or less the lens of choice for landscape photographers (with my lens mount) looking for a new lens after the kit lens. Honestly, I don’t use the 10 mm end that often because the perspective distortion is pretty severe, but it’s sometimes useful for shooting indoors. I do like the lens, and similarly to the 18-55mm, the minimum focusing distance is only a few inches in front of the lens so you can get really close to your subjects.

Tree [121 mm, f/5.6, 1/250 s, ISO-100]

As the fall went on, both Canon and Nikon essentially announced that they were shifting all new development to their mirrorless cameras, and Canon at least has been discontinuing many of their DSLR lenses. I still wanted a telephoto zoom lens, so when I saw a used EF-S 55-250mm f/4.5-5.6 IS STM for a reasonable price with an extra 10% off for Black Friday, I bought it.⁴ This lens is basically the telephoto equivalent of the 10-18mm, and I’ve enjoyed it so far, though I haven’t taken it on any big trips yet. The main drawback of this lens is its minimum focusing distance of close to 3 feet. After almost four years of being able to crawl right up to my subject, I’m not used to having to stand back a little. It’s fine for picking out details in landscapes, but I keep forgetting when I’m using it to magnify flowers and other nearby objects.

Moon (cropped) [250 mm, f/5.6, 1/320 s, ISO-400]

The 55-250mm lens is by no means a heavy⁵ lens, but I will say that switching from it to either of my other lenses makes the camera feel extra light. With my three lenses, I now have continuous focal lengths from 10-250 mm (10-18, 18-55, 55-250), with perhaps a slight dip in quality from 18-55 mm. I like the ultra wide/telephoto combination for landscape/nature photography to get overview and detail shots, but the 18-55 mm focal lengths are super useful for general purpose walking-down-the-street photography and indoors (e.g. museums, conservatories). I’m debating whether it’s worth picking up the STM version of the 18-55mm lens for the boost in image quality because I’ve seen it for less than a hundred dollars used, and I’d probably like to try out a “fast” (large aperture) prime lens (likely the EF 50mm f/1.8 STM, or maybe the EF-S 24mm f/2.8 STM) at some point to see what that’s about, but for now I’m happy with what I’ve got.

¹I’ve broken this down in another post, but the lens is made for a Canon crop sensor² camera (EF-S), its zoom range is 18-55 mm, the maximum aperture varies from f/3.5 to f/5.6 depending on the focal length, the lens has image stabilization (IS), and it’s the second version (II) of the lens.

²Camera sensors are a whole other rabbit hole that I’ve fallen down, and I might put together a different post on them.

³STM stands for the Stepper Motor used to autofocus the lens, and it’s a faster and quieter upgrade over the DC motor used in the kit lens that I have.

⁴Both the 10-18mm and 55-250mm lenses were $300 MSRP. I got the 10-18mm new for that price (+tax) and the 55-250mm used for around $170 total. The 55-250mm is officially discontinued, and the 10-18mm might not be, but it’s probably on the way out.

⁵For comparison, a super telephoto that someone might be reasonably walking around with (so not Canon’s EF 1200mm f/5.6 L USM lens that’s almost 3 feet long, weighs more than 36 pounds, and costs over $100,000) might weigh around 10 pounds.

The Camera

In February of 2018, I switched from a point and shoot camera (the Fujifilm FinePix XP55) to a DSLR (the Canon Rebel T6). By that time, most people were using phones as their primary photographic device, but I was not for a couple reasons – 1) since my first cell phone in college, I’ve had non-flagship TracFone phones with terrible cameras [my current phone is the first one I’ve owned that even has a front camera (that I essentially never use)], and 2) I’m legitimately quite awful at phone photography, to the point where there’s about a 50% chance any given photo isn’t even in focus. From a technological perspective, the XP55 actually has specifications that are comparable to an average phone camera from around 2018, but the point and shoot market has since been more or less obliterated by phones.

Icy grass [117 mm, f/8, 1/160 s, ISO-400]

Since I’m apparently not capable of getting good phone photos, I was still using a dedicated camera in 2018. After getting increasingly dissatisfied with the XP55, I upgraded to a DSLR. At the time, I knew that Canon and Nikon were two of the major names in the DSLR market and that the Canon Rebel series was frequently recommended for good entry level cameras. When I started shopping around online, the Canon Rebel T5 had been superseded by the T6 for close to two years and was getting harder to find. The T7 was, it turns out, weeks from being announced, and I didn’t know that I’d want any of the features (e.g. more megapixels and autofocus points) that made the T6i more expensive, so I ended up with the relatively affordable T6.

Squirrel [157 mm, f/5.6, 1/160 s, ISO-800]

Broadly speaking, a larger camera sensor tends to improve the overall “image quality,” increasing sharpness, how much you can crop or enlarge a photo, and low light performance. Going from the XP55 to the T6 increased my available sensor area by over an order of magnitude, so that was an immediate upgrade, even if I had stuck the T6 in auto mode and left it there. I was, however, also interested in learning about having control over aperture, shutter speed, and other settings, so I spent some time with photography books and dragging my camera a lot of places with me.

Trumpeter swans + ducks [121 mm, f/9, 1/160 s, ISO-400]

I’ve now had my T6 for just over four years, and taken close to 12,000 photos with it. My camera’s ridden with me on Amtrak to Chicago (twice), flown to Houston for the Society of Rheology annual meeting, gone to see family in Singapore, been dragged to Orlando for AIChE, visited Acadia, taken a trip to Michigan’s Upper Peninsula, and gotten biked all across and around Ann Arbor. As of late, most of the big players in the field are focusing their development on mirrorless cameras, but I’m still a fan of this entry level DSLR. I paid $330 for it new with the kit lens, so it’s not so expensive that you have to worry about every bump and scrape, but it’s still a nicely built piece of equipment that has plenty of capability, though not all the bells and whistles of a flagship camera.

The T6 doesn’t have in-body image stabilization, though all the lenses I have do. The general rule of thumb is to keep shutter speed faster than the inverse of the focal length, which I find works fine to get acceptably sharp photos, especially with my lenses rated for 3-4 stops¹ of image stabilization. The T6 also isn’t weather sealed, so I wouldn’t put it in a puddle or go out in a downpour, but it’s been fine in light to moderate rain and snow as well as cold. It further lacks a touchscreen, a tilt-out screen, and a live histogram (though does have live view, which I use on occasion), but I’ve never had any of those features so I’m fine without them.

The T6 has a bunch of photo modes, but I used auto for about one night to try out the camera, then it’s been in manual since then, and I’ve never taken video with it. I also don’t use burst mode, which is important for sports/action shots. I prefer shooting in full manual mode, but I use it very similarly to aperture priority a lot of the time, and I’m currently in a months-long trial of back button focusing², which I think I like. Although above around ISO-800, the noise starts being not great in certain situations, it’s a huge improvement over my point and shoot, so I’m not complaining too much. Overall, I’m very happy with the T6. It’s not the most brilliant camera out there³, and sure, I’d like to have the latest and greatest equipment, but the T6 is a more than capable camera for my adventures, and I’ve enjoyed my time with it so far.

[This post features photos from my newest telephoto lens. I also have a new-ish ultra wide-angle lens, which a lot of the photos from my Acadia and Upper Peninsula trips were taken with.]

¹Camera stops are a measurement of how much light the camera is seeing. One stop is half or twice as much light as the stop lower or higher than it. You get more stops of light by opening up the aperture, lengthening shutter speed, or increasing ISO. Image stabilization helps to eliminate blur caused by motion of the camera, which allows the shutter speed to be increased.

²Instead of half pressing the shutter to (auto) focus, you focus using a separate button on the back of the camera (hence back button focus). This decouples the actions of focusing and taking the picture, which allows you to set the focus where you want it, compose your photo, then take the shot instead of constantly having to refocus, assuming the focus point isn’t changing.

³It’s maybe just a little short on megapixels compared to newer cameras, and the lenses often aren’t the sharpest in the world, but since most people apparently only look at photos while scrolling through Instagram on their phone, no big deal, right?