Nope, actually the point of Sigma to make the 30mm 1.4 is to make a fast 1.4 "normal" lens that has a field of view close to a 50mm on FX. "I thought the point of a lens like this is to give a 30mm lens a 30mm field of view on a smaller sensor. Since they normally will have lens diameters smaller than FX lenses, they most of the time cost alot less compared to the FX counterparts. "So I guess my real question here would be, whats the advantage of using a lens designed specifically for APS-C sensors? " The 30mm is still going to give me 48mm field of view?" "Okay this is still leaving me a bit confused. I thought the point of a lens like this is to give a 30mm lens a 30mm field of view on a smaller sensor. So I guess my real question here would be, whats the advantage of using a lens designed specifically for APS-C sensors? The 30mm is still going to give me 48mm field of view? Okay this is still leaving me a bit confused. Sorry I meant the crop factor with the camera with the lens not of the lens. Therefore, 30mm is close to this when paired with your 7Dīeing built specifically for APS-C mean that while it will fit on a full frame camera the image circle it produces is not big enough to cover the entire sensor and therefore gives heavy vignetting. The 30mm will effectively be 30x1.6= 48mm on FF equivalentĥ0mm on FF is like the standard view. But because your 7D is a APS-C Sensor DSLR with 1.6x crop factor. A 50mm lens will have a much tighter angle of view on your 7D than the Sigma will have.Ĭheck out the Wikipedia article on crop factor for some handy illustrations. The Sigma 30mm is a normal lens built for APS-C cameras and it's closely comparable to a 50mm lens on a full frame/35mm film camera. Knowing that is handy, for example, if you need to know what focal length will give you the same, or similar, angle of view on crop frame/APS-C camera, as you are used to with a full frame/35mm film camera. The diagonal of the film frame is about 1.6 times longer than that of the Canon APS-C, which is why the crop factor is 1.6x. Here's a fine example of what will happen if you use the Sigma 30mm on a full frame camera. Use the lens on such a camera and you'll get vignetting. When Sigma says that the 30mm is designed specifically for APS-C sensors, what it implies is that the image the lens projects won't cover a larger sensor, such as a full frame digital sensor, like that of the 5D, or a 35mm film frame. The focal length is still the same it's the sensor that is smaller. Thus a lens of the same focal length on the 7D will have a narrower angle of view. The smaller sensor of the 7D will not see as much of the image the lens projects as the 35mm film frame. Now, imagine the same lens being used an a 35mm Canon EOS and your 7D. Canon went with a sensor which is slightly less than half the area of a 35mm film frame. Do you have any zoom lens, EF or EF-S, which covers 30mm? That's the angle of view the Sigma 30mm is going to give you.īack before APS-C DSLR cameras became pretty much standard, 35mm film cameras had been pretty much the standard. Any lens which will work with your camera will have the focal length marked on the lens. If you just use that 7D, then you can safely forget it. It will be 30mm on your 7D.Ĭrop factor can be incredibly confusing and is really something you can disregard unless you use cameras with different sensor sizes. Originally posted at 1:53PM, 7 April 2011 PST "Framing like a 48mm lens on a full-frame body, the Sigma 30mm f/1.4 EX DC HSM Lens is as close to a classic 50mm lens as 1.6x body users can get." Is it going to be 30mm or 48mm equivalent on my 7D?īecause in some reviews I read they talk about it being 48mm equivalent, which is confusing me as to what the point of a lens designed strictly for smaller sensors is if there is still a crop factor. With it being designed specifically for APS-C sensors, is there one? I'm confused about the actual crop factor of this lens.
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