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Thread: 24mm-70mm L2.8 USMI

  1. #1
    RFM3
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    24mm-70mm L2.8 USMI

    Upfront - I'm a newbie (sortof) with an expensive lens. So be gentle...

    I have a Rebel T1i with a 24mm-70mm L2.8 USMI. Bought it because I wanted sharp pictures. Also thought that because of 2.8 I could take better pics in lower light without flash.

    In Av Mode, I've noticed that in moderate light, afternoon shade, with 2.8 selected - it chooses a very slow shutter speed say 1/30 or more. If I pop the flash, it goes even slower. Does that sound right? Seems counter intuitive.

    In the auto modes, it does vary speeds and apertures, as well as ISO.

    In Tv mode, taking same pic at a faster speed 1/200, it will choose 2.8 and the pic is only slightly less exposed.

    Am I just over my head with the lens or does it sound like something is wrong. Any diagnostics that anyone can suggest? Open to input/comments.

    Thanks

  2. #2
    RFM3
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    Re: 24mm-70mm L2.8 USMI

    Still looking for some input. I apologize for the newbie question. Would appreciate any help.

  3. #3
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    Re: 24mm-70mm L2.8 USMI

    Take a look at your metering. I don“t know the specifics of your camera, but one place that most assuredly will have answers for you, would be photography-on-the.net.

    The onboard flash of your rebel will get in trouble illuminating pretty much anything due to the size of your lens hood.

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    Re: 24mm-70mm L2.8 USMI

    In Av mode, the speed will depend on the iso setting. In Tv mode the aperture will depend on the iso setting. In Tv mode, If you've set it to 1/200, and the iso is set too low, the aperture can not go lower than 2.8 - so you get what you get. I guess your iso is set too low for both Av and Tv.

    I generally use Av to get the depth of field I want, then adjust iso so I get a shutter speed I'm happy with. The 24-70 is normally on my camera, but as arild said, the camera flash will be pretty useless.

    Best wishes,

    Ray

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    Re: 24mm-70mm L2.8 USMI

    Stay in AV mode so you can keep your aperture at 2.8 or wherever you want it. Adjust ISO to compensate till you hit 1/125 or higher. You could go slower if you want or faster if you have a moving subject. Not knowing what your lighting condition is, likely you will start around ISO800 and go up.

  6. #6
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    Re: 24mm-70mm L2.8 USMI

    This is a strange lens although it is also a good lens. I don't have sharpness issue with this lens but I think its distorition character is not of Canon's best. For a lens of 27-70 range people would believe the 70mm end will have less distortion than the 24mm end but it is just the opposite, making shooting protrait to need to be more careful to put the subject (particular the face) not too far from the denter. Anyway, modern technogy has helped a lot in post lens correction, but I have this lens for son long and those days I use this lend was pre-lens-correction era. Anyway, as long as you know this lens, it is still quite good.
    Sharpness is a tricky business because not all the image looks the best when it is the sharpest - but you can adjust this in post if you shoot raw, provided the original image is ineed in sharp focus.
    Since you did not provide an iamge so it is difficult to provide more useful comment but achieving sharp image has issues concern in distance to the subject - the further away the slower shutter speed is tolerated, and closer, needs faster. The wider the lens, you can have the shutter speed a little slower and longer lens faster speed. The old fashion understanding on reciprocal is that you need spped 1/focal-length in use (for example 100mm you need 1/100s) but with increasing megapixels, today you probably need 2 X 1/focal-length in use for camera such as Nikon D800, for 1DsIII/5D2/5D3 - may be 1.5 X 1/focal-length of lens in use.
    In fact, today's modern DSLR is very good, simply try program will do a lot of help.
    And try not to hate the flash so much, there are million ways of using flash - creatively, it does not always just do to lighten up the subject, what it does is also adding some contrast, separate subject from background and so on, it can be use in a way that almost invisible, that's why there are so many more control on your build-in flash or those external unit from Canon.

    BR,
    Pingang




    Quote Originally Posted by RFM3 View Post
    Upfront - I'm a newbie (sortof) with an expensive lens. So be gentle...

    I have a Rebel T1i with a 24mm-70mm L2.8 USMI. Bought it because I wanted sharp pictures. Also thought that because of 2.8 I could take better pics in lower light without flash.

    In Av Mode, I've noticed that in moderate light, afternoon shade, with 2.8 selected - it chooses a very slow shutter speed say 1/30 or more. If I pop the flash, it goes even slower. Does that sound right? Seems counter intuitive.

    In the auto modes, it does vary speeds and apertures, as well as ISO.

    In Tv mode, taking same pic at a faster speed 1/200, it will choose 2.8 and the pic is only slightly less exposed.

    Am I just over my head with the lens or does it sound like something is wrong. Any diagnostics that anyone can suggest? Open to input/comments.

    Thanks

  7. #7
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    Re: 24mm-70mm L2.8 USMI

    RFM3: I don't want to make too many assumptions, so I'll share how I tend to orchestrate certain camera settings to start you off! Hopefully it'll get you somewhere to find out if it is camera settings or the lens.

    Firstly, I tend to shoot in Aperture Priority, AV mode. (This is usually about how much depth of field you want to control, also the wider the aperture, the faster the shutter speed)
    So typically I like to shoot wide open at f/2.8 in this case.

    General rules for ISO I tend to abide by: (rules are made to be broken)
    ISO 100 for daytime outdoors.
    ISO 400 for decent Indoor lighting.
    ISO 800 and higher for less than decent (moderate) indoor lighting. Higher ISO without flash will be your friend here... but not too far, because you will find your foe: NOISE)
    Typically, I'd like to shoot 1/60 (1/ focal length is good starting point) with something like this zoom lens, and 1/125 and faster will ensure better freezing of subject (people posing)

    Flash typically has a x-sync speed of 1/200, unless you can set to high speed sync. (Lets not worry about this too much now)
    TTL (Through the Lens) flash setting is good way to start!

    My biggest disclaimer for having said all this, try a test: shooting in day time (good lighting) at a landscape scenery or with one subject standing still for you. Shoot in Av mode, set aperture to ISO 100 (and then ISO 200 up to ISO 400, 3 shots), set aperture to f/8 and see how sharp the results are. You can try planting the camera on a tripod if you have one) Hope this helps!

    (And if still not satisfactory, you can post your results with settings and I am sure others can help you from there!)
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