In last week’s post, “The Hook-Up – When Bodies and Lenses Get Mounted,” I spent a lot of words covering an important aspect to mating lenses and camera bodies. For those of you who already have DSLR, and some experience with lens mounts, I apologize if it was a little fundamental, but hopefully the history included in the post was at least interesting. If you are new to the world of SLR/DSLR, it hopefully demonstrated the main point that not all cameras and lenses will work together. This week I’m taking a dive into a topic that affects not only your choice of a camera body and lenses, but also has implications for how well you camera combats noise. A note for P/S camera users, this one affects you too. Also, let me reiterate that this blog is primarily about DLSRs and occasionally P/S cameras, but if you are looking for information on digital medium format cameras or other varieties, you may still find some of this information relevant even though I may only briefly mention them. So now into the world of sensor size…
Back in the 1940s and 1950s, when film SLR cameras were first coming on the scene, the format of choice for capturing the actual photograph was 35mm film. Life was pretty simple as far as size went. The real area of choice was which brand and specific line of film you wanted to use as each one had slightly different characteristics. Also you had to choose between black and white or color film (although all early film was black and white). The differences were in the chemistry used to create the particular blend emulsion that was applied to the plastic substrate to react to the light. But, with all of that, there was just one size for SLRs. Even when compact point and shoot cameras came out, they still used 35mm film. As an aside images on 35mm film are actually 36mm x 24mm per frame. The term 35mm film (more accurately known as 135 film based on the standard developed by Kodak) refers to the width of the film including the perforations on the edges allowing the film to be advanced.
When Nikon was designing the first consumer digital SLR, the Nikon D1, prior to its launch back in 1999, they had to make a decision. Do they keep the standard full-frame sized sensor, or to they make it smaller? At this time they could easily make image sensors smaller than full frame. If you did or did not know, digital sensors have been in use in government and industrial applications since the 1970s, the first electronic point and shoots came out in the 1980s with first Sony Mavica, and the first true digital point and shoot cameras in the 1990s. However the extra area required for SLR style photography, with lower pixel density (remember the D1 only had 2.7MP) would have been too expensive and potentially result in a worse photograph produced. So they developed the first DSLR to have a cropped sensor, which they have since trademarked as the DX size sensor. All that is meant by cropped sensor is that the area of the image sensor is smaller than the standard 35mm frame (36mm x 24mm). For the DX sensor the dimensions in height and width is 1.52x (known as a crop factor) smaller than a standard 35mm frame. As a result is has an area only about 42% of the 35mm frame. The DX sensor size is in a class of image sensors with sizes similar to the Advanced Photo System – Classic, or APS-C, film size. Other manufacturers have similar sized sensors that also are classified as APS-C, but they are all slightly different in dimension. There are also sensors that are similar to the slightly larger APS-H film size and some that are smaller such as the Four Thirds standard size. Here are some of the common brands and their sensor sizes for medium format, DSLR and point and shoot cameras:
Camera Type | Camera Brand | Sensor Type | Aspect Ratio (W:H) | Height | Width | Area | Crop Factor* |
Medium format | Multiple | Medium format film, Medium format digital | 4:3 | 36 mm | 48 mm | 1728 mm2 | 0.75x |
SLR/DSLR | Multiple | 35 mm film, Full-frame digital SLR | 3:2 | 24 mm | 36 mm | 864 mm2 | 1x |
Canon Kodak Leica | APS-H | 19 mm | 28.7 mm | 545 mm2 | 1.3x | ||
Nikon (DX) Pentax Sony Fuji | APS-C | 15.7 mm | 23.6 mm | 371 mm2 | 1.5x | ||
Canon | APS-C | 14.8 mm | 22.2 mm | 329 mm2 | 1.6x | ||
Sigma | Foveon X3 | 13.8 mm | 20.7 mm | 286 mm2 | 1.7x | ||
Olympus Panasonic Leica | Four Thirds | 4:3 | 13 mm | 17.3 mm | 225 mm2 | 2.0x | |
Point and Shoot (Compact Digital) | Multiple† | 1/1.6” | 4:3 | 6.01 mm | 8.08 mm | 49 mm2 | 4.3x |
1/1.7” | 5.70 mm | 7.60 mm | 43 mm2 | 4.6x | |||
1/1.8” | 5.32 mm | 7.18 mm | 38 mm2 | 4.8x | |||
1/2” | 4.80 mm | 6.40 mm | 31 mm2 | 5.4x | |||
1/2.3” | 4.62 mm | 6.16 mm | 28 mm2 | 5.6x | |||
1/2.5” | 4.29 mm | 5.76 mm | 25 mm2 | 6.0x | |||
1/2.7” | 4.04 mm | 5.37 mm | 22 mm2 | 6.4x | |||
1/3” | 3.60 mm | 4.80 mm | 17 mm2 | 7.2x | |||
1/3.2” | 3.42 mm | 4.54 mm | 16 mm2 | 7.6x | |||
1/3.6” | 3.00 mm | 4.00 mm | 12 mm2 | 8.7x | |||
1/4” | 2.40 mm | 3.20 mm | 8 mm2 | 10.8x | |||
1/6” | 1.80 mm | 2.40 mm | 4 mm2 | 14.1x | |||
1/8” | 1.20 mm | 1.60 mm | 2 mm2 | 21.7x |
*Relative to the standard 35mm film frame.
†Unlike DSLR cameras, often manufacturers of point and shoot cameras do not stick with a single size sensors between its lines of cameras. Selecting the sensor size is secondary to the size and ergonomics of the camera, whereas, often size and ergonomics in the DSLR are designed around the image sensor chosen for its image properties.
There is a note on similar formats above. The height and width, and as a result the area and crop factor, may vary slightly between manufacturers and also between individual camera models from the same manufacturer. For example, the Nikon DX crop factor is actually 1.52x, whereas Pentax is 1.53x or 1.54x depending on the particular model. As another example, the Leica M8 sensor is an APS-H size but it actually has a crop factor of 1.33x rather than 1.28x for the Canon 1D MarkIII and the 1.29x for the 1D MarkIV. It should also be noted that this is also true for users of full-frame and medium format cameras, with sensors only being approximately the size of the standard 35mm and medium format film frame, respectively. For example the full-frame Nikon FX sensor in the D3 is actually 36mm by 23.9mm. The thing to take from this is that the slight variances in this dimensions of the sensors do not make a significant difference between similar camera types that a photographer would notice until the difference approaches 0.1x (why the Canon 1.6x crop factor is listed separately from the other 1.5x crop factors, but both are APS-C).
The consumer digital SLR world was born with Nikon DX crop sensor and it looked to stay that way. In fact, Nikon even stated that there would never be a need to produce a DSLR with a full frame sensor as there was no need. Cropped sensors were capable of producing great images and all pre-existing lenses would work as they produced an image circle that was meant for full-frame film, so it would obviously cover the smaller area of the APS-C sensor. So why, in 2011 at the time of the writing, do we have DSLRs that have full-frame sized sensors. For that we’ll have to take a look a little deeper in to the world of cropped sensors, their sizes, their advantages and disadvantages, and also the advantages that were discovered by having a larger image sensor area.
Let’s say you are at the local camera shop looking to buy a new, or perhaps your first, DSLR. You have narrowed it down to brand and features, but there are two camera models that are exactly the same except one utilizes a 1.5x crop sensor (let’s call this CropPhoto) and the other uses a full-frame sensor (let’s call this FullPhoto. Which do you choose? They both have the same number of pixels, so what’s the difference? Well, there are a few differences, most of which will be noticed while practically using the camera and at least one major point that actually makes a difference from the technical quality of the photograph produced.
Functionally the camera works exactly the same. On both cameras you attach the same lens (for the sake of this argument we will say a standard lens designed for a 35mm SLR, more on this in a bit), you focus the light the same way, and you capture the photograph the same way by actuating the shutter. However, because of the smaller size of a cropped sensor, you perceived focal length is actually different. But, isn’t focal length was a function of the lens? Well yes, you are right, but there’s more to it. Focal length is a function of the lens, however the perceived focal length is a function of the size of the sensor, whether it be film or digital. What’s the difference? Lenses are designed to focus light on to a single plane (the sensor of the camera). The image circle created by the lens is exactly the same when mounted on CropPhoto as it is when mounted on FullPhoto. The difference is that although the image circle is the same, the area of the image that hits the image sensor differs. Here’s a simple drawing to show you what I mean:
As you probably can already tell, the CropPhoto camera captures less area of the image circle on the sensor as compared to the FullPhoto camera and its full frame sensor. As we already established, these two cameras have the same number of pixels on the sensor, and as such can assume that the pixels on the cropped sensor are smaller than those on the full frame sensor (a good assumption). As such, if you were to take the same image from each sensor and make the pixels the same size you would see that the area captured on the cropped sensor appears to be taken with a lens with a longer focal length. That’s what a perceived focal length is. Although using the same lens, the image produced is zoomed in a little bit.
Well, what does this mean? Well by using the crop factor above, you can actually figure out what the perceived focal length is. Say the lens you are using has a focal length of 100mm. This lens has a perceived focal length of 100mm on the full frame sensor. For this example, the cropped sensor has a crop factor of 1.5x, meaning it has a perceived focal length of 150mm (1.5 x 100mm = 150mm). Ok, so perceived length of my lens is longer, so what? Well if we started with a cropped sensor size, then there would not be much impact, but as most equipment and photographers are calibrated to work using 35mm film or the digital equivalent, this means that all of a sudden, you normal 50mm lens, isn’t so normal any more. It’s actually no considered a short telephoto as it has a perceived focal length (also commonly referred to as the “35mm equivalent focal length”) of 75mm. Also, it means for all you birders and astrophotography guys, it means your 300mm telephoto lens, just got a bump to a super-telephoto at a perceived focal length, of 450mm or even better your 600mm just went nuts out to 900mm. Pretty awesome, right? Well kind of. It also means your 14mm ultra wide angle, just got less wide at 21mm, and the 85mm lens you loved using for portraits, just got a little long at 127.5mm. Also, as the world is still calibrated to 35mm frames, there is no a little bit of math involved to figure out which lens works best now. For new photographers, this isn’t so bad, and it takes a little adjustment if you have already used to working with full-frame. Cropped sensors have advantages at the long end at a trade off of disadvantages on the short end. Now lens manufacturers have combated this disadvantage by releasing lenses with even shorter focal length to regain that ultra-wide angle segment. For example I have a 10-24mm wide angle zoom which has a perceived focal length of 15-36mm, the low end of that being right in there with a 14mm ultra-wide lens however it is designed for cropped sensors, another concept I’ll explain now.
Lens manufacturers also found a benefit of the cropped sensor. They could now design lens that would produce a smaller image circle. Fortunately for the manufacturers, this actually means less glass, less engineering and less cost, while the photographer received lens with a little less weight and lower prices. Great, right? Well, as I mentioned above, the world of cameras in strewn with a myriad of different sized sensors, and there is still very much a preference for the full frame size. What this means is that unfortunately for the photographer, a lens designed for a cropped sensor camera will not work properly on a full-frame camera, however the opposite is not true. This picture illustrates why this happens (and please recognize that this is a conceptual drawing and now scaled to the actual dimensions of the sensor or circle size).
Now a huge deal if you stick with cropped sensor cameras as you have your pick of lenses from both groups, but if you ever upgrade to a semi-pro or professional camera with a full-frame sensor, you will not be able you use those lenses to capture a full-frame image. The cropped lens with severely vignette (meaning a significant drop-off in light) at the corners and edges of the frame. So if you have plans to upgrade in the relatively near future, it may best to stick with lenses designed for full frames so you can keep using them with a new camera. I personally have a mix of DX (Nikon’s cropped sensor designation) and full-frame lenses as I realize it will be some time before I upgrade to a full-frame camera, and also that Nikon’s full-frame DSLRs allow you to shoot in DX mode, where it will only use the middle of the sensor (a sacrifice in image size, but with a benefit of compatibility). Again, it’s a personal choice based on your plans for your future photography needs.
So, there are two difference or considerations that have to do with the photographer and how you use, and purchase gear. But what about image quality? Are they the same? For the most part, yes they are, but with one big advantage in low noise operation for the full-frame sensor. Because of the larger sensor size, the same number of pixels can be spaced out, and a little larger, a lower pixel density. And though you may think you want more pixel density; this is only true if you have good control over noise. With a lower pixel density due to a larger sensor, a pixel that is excited by light photons, it is less likely to create excitation or noise in the surrounding pixels. So while you maintain the same number of pixels, you effectively get a bigger reduction in noise. This is also true for cameras with really a really high number of MPs, although I get to that in another post. To clarify, this is most important in low light situations, and for things like astrophotography. For most everyday photography, you will be hard pressed to find differences between two pictures from two equal cameras with difference sized sensors. In the real world, that’s when other factors come into play to want a full-frame camera as there are not two equal cameras. Typically full-frame cameras are professional models and have other features, better image processors, easier to use, etc.
Lastly, the full-frame cameras are more expensive. Not only because they tend to be in professional level cameras, but because the sensors are more expensive to make, and therefore the cameras are more expensive to produce and this cost is passed on to the consumer.
There is a lot of information to know and understand about all aspects of photography and cameras, and I hope this was informative. I probably went into more detail than most people want or care to think about, and there is even more I didn’t touch on. The point of this was to highlight the differences and considerations to take into account when comparing cameras with cropped and full-frame sensors, and could be the difference between getting the Nikon D300s and the Nikon D700, but again it is all up to you, as long as you get the tools you want so you can get out and shoot comfortably and focus on the photographs, not the camera.
No comments:
Post a Comment