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02-10-2012, 02:10 PM   #1
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Why IF matters?

Hi,

I wonder what is IF (regarding lenses) and why does it matter? Is IF lens better than non-IF one?

Thanks,
c3p0

02-10-2012, 02:17 PM   #2
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Internal Focus. The lens doesn't extend and retract, and is less likely to suck in dust.

It's not that big of a deal in practice.
02-10-2012, 02:19 PM   #3
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IF typically stands for 'internal focus', meaning the front lens element does not rotate while focusing. Very useful for those of us who use polarizers and graduated filters.
02-10-2012, 02:20 PM   #4
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QuoteOriginally posted by Docrwm Quote
IF typically stands for 'internal focus', meaning the front lens element does not rotate while focusing. Very useful for those of us who use polarizers and graduated filters.
Two separate things. Only two of my lenses are internal focus, but all of them have a front element that does not rotate while focusing.

All internal focus lenses don't rotate, of course, but many/most lenses sold today don't rotate, either.

02-10-2012, 02:31 PM   #5
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IF lenses aren't necessarily sealed from dust. FA* are good examples. What so great about IF lenses is that less mass will be driven by AF motor, and their bodies can be made with less moving parts so they can withstand more minor impacts.
02-10-2012, 02:32 PM - 1 Like   #6
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It generally makes AF faster and doesn't extend the lens so higher-end lenses have IF (and sometimes even internal zooming).

Adam
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02-10-2012, 02:47 PM   #7
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The basic difference as people have said is the lens does not extend when focusing, and yes it reduces the mass for the AF motor to move, making AF potentially more responsive, as well as reducing the demand on the battery. But AF lenses achieve focusing by modifying the focal length. As a result the closer you focus the shorter the focal length gets. Normall it is not a big deal but it can be wine dealing for example with macro, because shorter focal lengths mean reduced working distance
02-10-2012, 04:38 PM   #8
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Lowell nailed it. We have various threads here about LENSMAKER CHEATING and MY 250 ZOOM ONLY GOES TO 200 and the like. What happens is, IF changes focal length and focus distance together. An extreme example: with my Schneider Betavaron 50-125 enlarger zoom, built to be fixed-focus. I can change the focus distance, but only by changing the focal length. So at 50mm (on about 32mm of extension) it focuses to infinity, whilst at 125mm it only focuses to about 1.5m. Without a focusing helicoid, using it is a weird dance of focus and framing and magnification. Camera IF zooms aren't so nutz but they still show that effect.

02-10-2012, 04:51 PM   #9
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Didn't the Nikon 18-200 only go to 135 for 'macro' shots or something like that?
02-10-2012, 05:03 PM   #10
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It's also nice for us who shoot hockey or aquariums. Having an extending lens while pushing the lens against glass isn't a good idea at all.
02-10-2012, 05:30 PM   #11
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QuoteOriginally posted by VisualDarkness Quote
It's also nice for us who shoot hockey or aquariums. Having an extending lens while pushing the lens against glass isn't a good idea at all.
Good point although I find a rubber lens hood works wonders
02-10-2012, 06:12 PM   #12
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If I understand everyone here, you are just talking about the actual actions during focusing. I know some on the internet people will say that IF means the lens doesn't extend during zooming (ie the lens barrel is fixed in size). I know that this is not true as the Tamron 28-75 claims to be IF and it very much extends during zooming.
02-10-2012, 06:21 PM   #13
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IF & IZ are 2 separate designs.
02-17-2012, 12:11 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote
The basic difference as people have said is the lens does not extend when focusing, and yes it reduces the mass for the AF motor to move, making AF potentially more responsive, as well as reducing the demand on the battery. But AF lenses achieve focusing by modifying the focal length. As a result the closer you focus the shorter the focal length gets. Normall it is not a big deal but it can be wine dealing for example with macro, because shorter focal lengths mean reduced working distance
Do all AF lenses achieve focusing by modifying the focal length? Or it should be "IF" instead of "AF"?
02-17-2012, 01:27 AM   #15
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QuoteOriginally posted by MSM Quote
If I understand everyone here, you are just talking about the actual actions during focusing. I know some on the internet people will say that IF means the lens doesn't extend during zooming (ie the lens barrel is fixed in size). I know that this is not true as the Tamron 28-75 claims to be IF and it very much extends during zooming.
Some on the Internet are misinformed, clueless, or just plain-old stupid. The problem is that they are unaware of that fact and are more than happy to share their misinformed, clueless, or plain-old stupid opinions as informed and enlightened wisdom.
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