 Joey Sheeley |
Wide angle lens... I'm looking for a decent, not-terribly-expensive wide angle lens for my Rebel XT. It came with an 18-55mm, but I'm looking at this lens: Sigma 17-35 mm F 2.8-4 EX DG Aspherical Autofocus. The price is right for an amateur, but would like to know if anybody has experience with it and/or would recommend it.
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Alan N. Marcus |
Hi Joey, We fit lenses on cameras based on the size of the digital sensor at the rear of the camera. This is what captures the image when you press the shutter release. Your camera’s sensor size is 14.8mm by 22.2mm. Next we calculate the diagonal of this rectangle. Doing the math that works out to 26.7mm. Knowing this value is important because we use it to determine what lenses to mount. Generally a wide-angle starts at 70% of the diagonal. Again doing the math, that’s about 18mm. Thus for wide-angle you want a lens 18mm or shorter. When a lens is mounted that about equals the diagonal measure, the angle of view, as seen by the camera, is about 53° which is considered normal. A telephoto is generally considered to be about 200% of normal. For this camera that’s about 55mm. What I am trying to tell you is: The kit lens that came with your camera is a zoom with a range of 18 ~ 55. This range covers the beginnings of wide-angle through the beginnings of telephoto. This one centers on normal. The Sigma 17 ~ 35 offers little in the way of wide-angle, being only 1mm shorter than your kit lens; it offers no advantage as to field of view. If wide-angle is your heart’s desire, you need to choose a zoom with a shorter focal length. Likely others will advise as to their favorite model and focal length range. Alan Marcus (marginal technical gobbledygook)
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Joey Sheeley |
Thanks for the information, Alan. I wondered if I'd be gaining anything. The biggest difference I saw was the min. 4.0 ap on the one I have vs. 2.8 on the Sigma. Am I correct in assuming that if I want to get the really wide angled lens with a much bigger minimum ap, I'm going to be looking at a larger investment. Always looking for the cheap solution, Joey :)
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Alan N. Marcus |
Hi again Joey, The difference between f/4 and f/5.6 is one f/stop. The f/4 lens, when set to maximum (wide open), allows twice as much light to play on the digital sensor. One f/stop is not a lot but can make a difference. As an example in dim light, at max aperture f/5.6 let’s assume the shutter speed works out to 1/15 sec. Now some people can hand hold, without blur but it’s always iffy. Mounting the lens allowing f/4 as maximum, you would be able to raise the shutter speed to 1/30, now the likelihood against of blur is much improved. One can compensate for the difference of 1 f/stop by upping the ISO. One f/stop is equal to a doubling of the ISO. Say your camera is set to 100 ISO. Changing to 200 ISO affords 1 f/stop more sensitivity, that would allow you to up the shutter speed by one notch. Everything comes at a price! Upping the ISO yields more noise. Noise in digital photography is the equivalent of detail destroying grain, a dreaded phenomenon in chemical photography. Noise and grain creep in when you push the envelope. Upping the aperture f/5.6 to f/4 diminishes depth-of-field. There is no free lunch is this business. Alan Marcus (marginal technical gobbledygook)
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- Carlton Ward Contact Carlton Ward Carlton Ward's Gallery |
Hello Joey, You may check out the Tokina 10-17mm or the Canon 10-22mm for super wide. You will still be dealing with the 1.6 crop factor of your Rebel XT sensor and these lenses will not work on a full frame camera (5D or 1D's) if you ever decide to upgrade to one of them. They do work on 20D, 30D & 40D. The Tokina got pretty good reviews & is cheaper than the Canon. Sigma makes one in this range but if I remember correctly, the reviews were not very positive. Good Luck, Carlton
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Joey Sheeley |
Thanks, both of you, for your help. Lots to review and think about. Joey
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