Digital Canon Lens Question

[NewPhoto]

Hi Everybody,

This is my first post to the forums. Also, I am VERY new to photography, so please excuse my ignorance if this question is simple.

I have a digital Canon EOS Rebel XT with a standard EF-S 18-55mm lens. I recently purchased a 100-300mm Canon EF telephoto lense f/4.5-5.6 with USM and rear focusing which, from everything I've read about the EF-S mount being backward compatible with EF, should work fine on my camera.

However, the lense has a considerable amount of blur, which seems to be worse upon zooming in on items. I'm 100% certain this is not my hands shaking, as I've set it on a stable surface with the same results. The blur is noticeable both while looking through the viewfinder and in the photos.

Is there anything I'm missing regarding the use of an EF lense on an EF-S camera? Is there a setting I need to adjust? Or is it a bad lens?

Any help with this issue would be great. Again I apologize if this is something obvious, this is my first real experience using a telephoto lense on my camera.

Thank you all.

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[fokker]

Please define the blur better, or better yet upload an example picture or two. It may just be that you are not focusing on the subject? Did you buy the lens new or second hand?

[bigtwinky]

You are correct in thinking that the lens fits on your camera, so thats not the issue.

I'm also thinking your blur is not blur but actually a focus issue. On the lens, you should see a little switch that goes between AF and MF.
AF = Auto Focus
MF = Manual Focus

If its on MF, then the auto focusing will not go on and depending on where the focus ring is, its going to be mostly out of focus. So make sure its on AF or that you use the ring to manually focus.

[NewPhoto]

Hi Everyone,

Thanks for the replies. Yeah, I know about the MF vs. AF, and both seem to function as they should, however the image never becomes clear. It's especially bad when I'm zoomed in to 300mm. I was unable to upload any of the photos unfortunately. It seems that in some instances the blur is mostly around the periphery of the image, while the center is sharp. It's bizarre. I can focus from blurry to almost sharp but then the image just gets blurry again as I keep focusing. The AF is very responsive and fast and results in the clearest possible image that I'm able to reproduce by using MF, but it's not sharp at all. At first I though there must be grease on the internal surface of the lense, but it's clear.

Anyway, I appreciate all of the comments and any additional ones as well. As long as I'm not missing some secret setting that I needed to manipulate to get this lens to work propertly on my camera, I'm sending it back. It's used, but was promised to be in great shape by the seller (of course...)

Thanks.

[SonnarSphere]

Hi Everyone,

I can focus from blurry to almost sharp but then the image just gets blurry again as I keep focusing.

do you get a focus-lock beep sound? this comment suggests maybe
the AF is continuing to hunt for focus.

as previously requested can you upload a picture and give us the exif
data? (the camera shot settings)

[tsaraleksi]

Are you talking about blurring of the entire image, like it's just soft or a bit fuzzy, or something else?

[Samanax]

Post a sample picture so we can see this "blur".

[tomhooper]

I shoot "L" glass on my XT. It is not a camera/lens compatibility problem. Focusing long glass is not easy but as others have said it would be nice to see some examples.

[Big Mike]

As mentioned, examples will really help.
How do I do that? A pictorial guide to using TPF.

Are you possibly trying to focus on something that is too close? Can you focus sharply on something that is farther away than say 10 feet?

[maulrat]

This is my first post to the forums. Also, I am VERY new to photography...

Without samples, my guess would be that you're shooting in auto mode with undesireable lighting conditions while zooming to 480mm without IS.