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Benefits of an APS-C sensor camera over 35mm sensor camera (Canon perspective, with 7D and 5DII in mind)
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There is a lot of confusion about the nature of cameras with the APS-C sensor size vs cameras with 35mm sensor size. Often the talk runs around image quality and I see that there is a general assumption that a DSLR with a 35mm sensor is always better. This is simply untrue. From a signal to noise ratio point of view, the camera with a 35mm sensor is better. But there is a lot more to photography than having the least possible amount of noise in your images.

a 50mm example:
If we compare, for example a Canon 7D and 5DII, we can quite safely assume that there is approximately 1.5 stops of difference in 5DII's benefit in signal/noise ratio in practical photography when we use for example a 50mm f/1.4 lens at the same aperture. If we use a 50mm f/1.4 lens in both cameras, the 5DII will be about about 1.5 stops better in noise/detail performance and it will also produce somewhat better contrast, especially with higher sensitivities.



However, there are other aspects to think about.
- The 50mm lens will give more vigneting on a 35mm sensor camera. Due to darker borders, you may need to increase exposure to capture an equally balanced exposure across the frame on the 35mm sensor camera or you will need to correct the vigneting in post processing. On some lenses (cheaper zoom lenses for sure), the border areas of the image may be relatively softer on the 35mm sensor sensor. - If you want the same perspective for both cameras, you will shoot the image from the same spot. However, if you want the same framing, you will shoot with the 35mm sensor camera from a closer distance or with the APS-C camera from further away. If you want to fill the frame with a small target (cat, kitten, puppy, small child in a close-up, flower, etc etc) the closest focucing distance of the lens may not be enough to fill the frame on the 35mm sensor camera and you will need to judge exposure of the needed framing more carefully (and compensate exposure value or switch to center weighted exposure mode) and also crop the image later on in post processing. - If you were to use an 85mm lens instead of the 50mm lens, you would certainly have trouble more easily with the closest focusing distance, because the magnification ratio of Canon 85mm lenses is even worse than 50mm lenses (85/1.2L - 0.95m, 0.11x / 1:9.1)(85/1.8 - 0.85m, 0.13x / 1:7.7)(50mm/1.4 - 0.5m, 0.15x / 1:6.7)


The following image demonstrates using the 50mm focal length on APS-C and 70mm on 35mm.



That's just one example in practical photogaphy. I wrote the following little list to clarify the benefits of using an APS-C DSLR. Most of the points have surely been made previously by other people somewhere, but I tried to be thorough and practical here and put all the stuff into a single list. You are more than welcome to add further advantages of the APS-C DSLR to this page, I will update this message to include significant advantages.

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advantages of an APS-C sensor DSLR over 35mm sensor DSLR:
- price /quality ratio of APS-C zoom lenses is usually better than with lenses designed for full frame. APS-C lenses are usually cheaper.
- it is possible to use both 35mm and APS-C lenses, a 35mm sensor Canon camera can't use lenses designed for smaller sensors properly
- lenses that are designed for full frame sensor have less vigneting on APS-C sensor cameras and some lenses may have better edge definition
- lenses designed for APS-C sensor tend to be significantly lighter (though rarely weather sealed)
- APS-C lenses usually have better closest focusing distance than 35mm lenses (e.g. Sigma 17-70 focuses so close, that objects can almost touch the front element).
- when photographing comparatively small targets, it is easier to fill the frame with 50mm lenses (all have 45-50cm closest focusing distance), 85mm lenses and many wide angle zoom lenses with APS-C sensor, due to closest focusing distange
- with macro lenses and telephoto lenses it is easier to fill the frame without cropping on an APS-C camera, advantage of 1.6x. With a 35mm sensor camera, you are more easily forced to crop.
- when the frame coverage of the target is small (small and/or faraway target), it is easier to place focus point on it on an APS-C camera, than with a 35mm sensor camera - the target is larger relative to the focus points. This is definitely easier to do on the 7D compared to the 5DII with the better non-central focuspoints and wider focus point spread.
- DOF advantage in macrophotography and often in landscape photography (with the same framing as with a 35mm sensor, you are further away from the target)
- there is no shortage of cheap ultrawide lenses (Sigma 10-20 f/3.5, Sigma 10-20 f/3.5-5.6, Canon 10-22 EF-S, Tokina 11-16, Tokina 12-24, Sigma 12-24, Tamron 10-24, Tamron 11-18....). For full frame, your choise of relatively cheap and light lenses are the Canon 17-40/4L and Sigma 12-24/f4-5.6
- large selection of cheap or moderately priced, quality wide angle image stabilized zoom lenses (Canon 17-55 IS, Canon 15-85 IS, Sigma 18-50/2.8 OS, Sigma 17-70/2.8-4 OS, Tamron 17-50/2.8 VC, Tokina 16-50/2.8 )
- speciality lenses for crop sensor like Tokina 10-17 fisheye and Tamron 60mm f/2 macro
- crop sensor cameras provide AF assistance with built-in flash
- large selection of light weight image stabilized travel zoom lenses (Canon 18-135IS, Canon 18-200IS, Tamron 18-270 VC, Sigma 18-200 OS, Sigma 18-250 OS). For a full frame camera there is not that many choises - the expensive and very heavy, but relatively high quality solution 28-300L and Tamron 28-300VC

compare the weight with a 35mm lens, for example:
Canon 18-200 IS: 595g
Tamron 18-270 VC: 560g
Canon 28-300L: 1670g


(Canon 18-200 and 28-300L, unfortunately not to scale)

some benefits of specifically 7D over 5DII:
- 7D has improved focusing system, 19 cross type focusing points and wider coverage of AF points through the image area (vs 5DII with one cross type sensor and the rest of the points are inconveniently more clustered around the center area)
- servo AF can be fine tuned (and probably _has to_ be fine tuned to serve individual preferences)
- 7D has several AF point grouping methods and spot focus possibility
- 7D can control external speedlites with the buil-in flash
- 7D has dual axis electronic level, convenient for architectural photography, ultrawide and fishey photography (and shooting test targets...)
- 7D has custom button functions
- 7D can shoot 8 frames per second, while with the 5DII it is 3.9 fps (I usually don't give a rat's ass about the fps, but some people need it)



And so that this doesn't end up sounding too much like a fanboy testimonial, we'll finish by summing up the benefits of a 35mm sensor camera over APS-C, more specifically
benefits of 5DII over 7D over 5DII:

- Well, the first and the most significant advantage is a 1-2 stop advantage in noise performance over 7D (it _does_ have a larger sensor...) Images will have less noise but also better contrast especially at higher sensitivities. The images will have a cleaner outlook in general. The difference is most visible at ISO's of 1600 and higher, where you will also have more detail in the images. I guess this is usually the most important factor for people choosing to use a 35mm sensor camera (it is for me). However, the difference in noise and image quality will only be visible at higher ISO's and comparatively large magnifications or in very large prints or if you need to severely crop the image.
- If you need large aperture lenses for wide angle photography, you need a 35mm sensor camera. This means approximately 35mm equivalent focal lengths of 24-35 at apertures of f/1.4 to f/2. If can manage with f/2.8, you're covered with an APS-C, if you need larger apertures, you need the 35mm sensor. The lenses that can be used to achieve the combination of wide angle and large aperture would be the 24mm f/1.4L, 28/1.8 and 35/1.4L.
- if you need the widest possible focal length, there is a 12-24mm solution for 35mm, the Sigma 12-24mm f/4.5-5.6 (it's not _sharp_ in the corners, but it get's the corners). You can't get an angle of view this wide on the APS-C, except with a fisheye. Nikon has a full frame lens 14-24, which is also wider than the crop sensor lenses that start from 10mm. (update 2/2010: actually Sigma has now released the APS-C focal length range equivalent of the 12-24mm lens and it's called the 8-16mm F4.5-5.6 DC
- Also, TS-E lenses are usually most useable on a 35mm camera (TS-E 17mm f/4L, TS-E 24mm f/3.5L, TS-E 24mm f/3.5L II, TS-E 45mm f/2.8,TS-E 90mm f/2.8 )
- you can achieve a bit more shallow DOF shooting middle distances (but in close up photography may be limited by closest focusing distance). A more shallow DOF is often an advantage in portrait photography in available light
- interchangeble (matte) focusing screens. These come in handy when you use manual focus lenses and need to determine point of focus (this includes for example Zeiss and Voigtländer lenses with a Canon mount, TS-E lenses and the Canon MP-E 65mm f/2.8 1-5x Macro). You can't change the focus screen on the 7D (but can change it on x0D series cameras)
- you have more options of general purpose wide angle zoom lenses on a 35mm sensor camera that are weather sealed - 24-70/2.8L, 28-70/2.8L and 24-105/4L IS. Of course you can use these on an APS-C sensor camera, of which the 7D is the only one that is weather sealed, but you will lose the wide angle and thus the general purpose nature with the 1.6x crop. EF -S lenses don't come weather sealed. The only weather proof option for this purpose on 7D would be the 17-40/4L (translating to a 27-64mm f/4 lens after the 1.6x multiplier).


The following thumbnail is left there for technical reasons.
(otherwise this text will not show up at all in the main PBase gallery. It's just the same pic as in the beginning of this text)