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Old Jan 11, 2008, 12:25 AM   #1
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What does "IF" (Internal Focusing) mean? Is that Tamron's version of an in-lens AF focusing motor? And if so how quiet and fast are they?
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Old Jan 11, 2008, 12:47 AM   #2
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Internal focus allows use of polarizing filters, as it doesn't rotate the barrel of the lens in order to achieve focus. It also may change the size of the image on the sensor even though you haven't changed focal length. IOW, good for some things, not for others. I have a Tamron zoom with this feature, and it is not a problem for most outdoor shots. Can require some readjusment for close-ups, though. This isn't their designation for in-lens focus.

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Old Jan 11, 2008, 12:58 AM   #3
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VTphotog wrote:
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Internal focus allows use of polarizing filters, as it doesn't rotate the barrel of the lens in order to achieve focus. It also may change the size of the image on the sensor even though you haven't changed focal length. IOW, good for some things, not for others. I have a Tamron zoom with this feature, and it is not a problem for most outdoor shots. Can require some readjusment for close-ups, though. This isn't their designation for in-lens focus.

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So I take it Tamron doesn't make any lenses with an internal AF motor like the other third party manufacturers? I'm looking at third-party lenses w/ AF motors for a Sony mount (e.g. A700).
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Old Jan 11, 2008, 2:16 AM   #4
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Tamron do make lenses with internal AF motor. That depends on what model of camera the lens is for. Typically third party lens don't come with AF motor if the camera body already has a focus motor. That's starting to change with some lenses to compatible with the Nikon D40/D40x.

http://www.tamron.com/lenses/prod/diII.asp

http://www.tamron.jp/en/data/lenses/index.html
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Old Jan 11, 2008, 7:18 AM   #5
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'Internal Focus' means that, in order to focus, all that moves is a lens element (or elements) within the barrel. That is, the length of the lens doesn't change, and the objective lens doesn't rotate as the lens is focused.
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Old Jan 11, 2008, 1:42 PM   #6
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dr_spock wrote:
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Tamron do make lenses with internal AF motor. That depends on what model of camera the lens is for. Typically third party lens don't come with AF motor if the camera body already has a focus motor. That's starting to change with some lenses to compatible with the Nikon D40/D40x.

http://www.tamron.com/lenses/prod/diII.asp

http://www.tamron.jp/en/data/lenses/index.html
How can you tell if a particular Tamron lens does have an AF motor? Besides when they actually say so as in the case of their new 18-250.

Sigma has their HSM lenses. Tokina...I didn't notice any. Interesting.

And thanks TCav. Just noticed that Tokina lenses also come with IF. I suppose most comapnies do. But don't say so.
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Old Jan 11, 2008, 3:02 PM   #7
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DarkDTSHD wrote:
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How can you tell if a particular Tamron lens does have an AF motor? Besides when they actually say so as in the case of their new 18-250.

Sigma has their HSM lenses. Tokina...I didn't notice any. Interesting.
If a manufacturer says that the lens is autofocus on your camera, and it needs a motor, it will have a motor. The HSM is different. HSM motors are faster, but more important, they are almost silent (except, possibly, for dogs.) Sigma advertises the HSM feature because of these to advantages. It's non-HSM lenses will autofocus on all Canon dSLRs because Sigma puts non-HSM autofocus motors in them. It's non-HSM lenses will auto focus on Nikon dSLRs becasue they will use the autofocus motors in the bodies. That's why SIgma's non-HSM lenses won't autofocus on the Nikon D40 or D40x.

And Tokina lenses will autofocus on all Canon and most Nikon (not the D40 or D40x) camera bodies; they just don't have really fast, really quiet autofocus motors in them.

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Just noticed that Tokina lenses also come with IF. I suppose most comapnies do. But don't say so.
Actually, most lenses do change length as you focus. Sometimes only a little, but sometimes a lot. IF is atypical, and if a lens is IF, they're bragging about it.
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