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deepsouth
4th of June 2006 (Sun), 11:05
What do the EF-S IS USM mean? Is the 17-85mm EF-S IS USM a good Lens?

lakiluno
4th of June 2006 (Sun), 11:10
OK

You need to split it up.

The EF-S is the lens mount. The standard canon AF mount is known as the "EF" mount. EF-S is an extension of this. The EF-S lenses only work on cameras with a 1.6x smaller sensor than a 35mm piece of film. If you have a Canon 300D, 350D, 20D or 30D this lens will fit. If you have any other canon DSLR or SLR, it won't fit.

The IS means its image stabilised. This means sensors in the lens make an element move back and forward to counteract the effects of camera shake (aka when you do a long exposure and can't keep it still). This won't let you do very long exposures, but you can normally get 1-3 shutter speed stops slower.

The USM means Ultrasonic Motor. This is a type of AF motor that is almost silent. It is also normally quite fast at focussing.

Leo

crn3371
4th of June 2006 (Sun), 11:45
Leo got the definitions nailed, so I'll chime in on the lens itself. Like just about any lens, it has its supporters, and detractors. I personally have one, and like it very much. It has a very usable range, and the IS helps a lot in static, low light shots. For me, I find it a very good walkabout lens.

lakiluno
4th of June 2006 (Sun), 12:07
I got emailed by deepsouth (not sure why he/she couldn't use the forum)

Heres the contents of the email, for other people wondering the same thing and so I can be corrected if I said something wrong.

Thanks for your reply. I have a couple of other questions. Is the EF better to have than the EF-S? I am looking a buying a Rebel XT. If the stabilizer helps stabilize your picture but will not let you do long exposures, which is the best? Do you recommend that I do not purchase the IS?

Thanks

hey

It would be better replying in the forum

The stabiliser doesn't stop you doing long exposures. Basically,
whenever you take a photo, you move slightly during the photo. The
longer the photo is being taken for, the more you move. That causes
the photo to blur. The image stabiliser reduces this movement to a
point, so you can take longer exposures (lower shutter speeds) with
less blur from camera shake. It doesn't, however, completely stop the
camera shake, so if the shutter speed gets too low it can't do
anything. You can still take photos with the IS off on tripods or
monopods.

The EF-S lenses are made because the smaller sensor in some Canon
DSLR's doesn't make any use of the light around it. This is known as
the crop factor. Imagine that most lenses (all EF mount lenses) are
designed to make a circle of light big enough for a 35mm frame to fit
into and get a full image. If you use that same lens on a crop body,
some of the light hits the area around the sensor and isn't recorded.
An EF-S lens simply doesn't make a circle of light big enough for a
full frame 35mm sensor, so less glass is required and it is cheaper.

If you aren't planning on buying a full frame camera (such as the
Canon 5D or any Canon film SLR) in the near future, then the EF-S lens
is a good and cheap lens. Because of the crop factor (1.6x), most EF-S
lenses tend to be much wider than equivalent EF lenses. The 217-85 is
the equivalent of a 27-136mm lens on a full frame camera. I would
recommend you purchase this lens, or a lens equivalent to it (Sigma
17-70 for instance), as if you purchased a lens designed for full
frame cameras in this range it would be thousands of dollars.

Leo

crn3371
4th of June 2006 (Sun), 12:22
While I recommended the 17-85 IS lens, it isn't cheap, almost as much as the XT itself. If you are just starting out, I would suggest getting the XT with the 18-55 kit lens, and cutting your teeth with this package. Once you learn the camera, and the limitations of the kit lens, you can start investing in better glass. The kit lens is only going to add about $70 to the price of the XT. A good, cheap, starting point.

Bruce Hamilton
4th of June 2006 (Sun), 12:23
The EF-S lenses only work on cameras with a 1.6x smaller sensor than a 35mm piece of film. If you have a Canon 300D, 350D, 20D or 30D this lens will fit. If you have any other canon DSLR or SLR, it won't fit.

It should also be pointed out that because of the sensor size difference, a 17-85 IS is equivilent to a 28-135 on a non-EF-S camera. A 28-135 IS can be purchased new for substantially less than the 17-85 IS... Plus if you sell that EF-S camera and buy a 1DMK2, you won't be stuck having to sell a lens.

lakiluno
4th of June 2006 (Sun), 12:34
but if you bought a 28-135 you wouldn't have the same range. Just because its an EF-S lens doesn't mean that the focal length is different. a 28-135 lens would become a 45-216mm lens, so it would have no wide angle at all.

Bruce Hamilton
4th of June 2006 (Sun), 12:51
but if you bought a 28-135 you wouldn't have the same range.

Actually, that's not totally correct. ;)
The 18-55 kit lens is equivilent to a 28-90, which is a lens I used to have before I went on my buying binge of nothing but L glass, but that's another story. I tested that 28-90 on my 300D before I sold it, and it was wider than the kit lens on 18, and longer than the kit lens on 55.

cdifoto
4th of June 2006 (Sun), 12:56
:rolleyes: His point is you don't have a true focal length either way. You ALWAYS have to take into account the crop factor, EF-S or not. :rolleyes:

blonde
4th of June 2006 (Sun), 12:59
how is that possible that a 28 will be wider than 18mm??

Jon
4th of June 2006 (Sun), 13:14
Now look, people, don't make me come down there with a club and start breaking heads for starting another cra^hop factor bit.

Focal length is an absolute property of a lens. NO MATTER WHAT CAMERA IT'S USED ON. It affects how perspective is captured.

The crap factor is strictly a property of the sensor. The 350D and its class have a sensor that's smaller than the "standard" 35 mm format. The ratio of the two is 1.6. So the field of view of any lens on a "crop" sensor is smaller than the samew field of view on a FF camera. In fact, the FoV (and only the FoV of a lens on a 1.6x crop (APS-C)camera is the same as that of a lens with a focal length 1.6x longer on a FF body. But the image size you capture on the cropped sensor is exactly the same size as the center 22.5 x 15 mm section of a 35 mm camera using the exact same lens. There is no magnification. The only reason there seems to be any is that you need to enlarge a 22.5 x 15 mm image more than you do a 36 x 24 mm image if you want to get a given print size. That "empty" magnification (you don't capture one whit more detail in the process) is, surprise, surprise, 1.6x more. And that magnification post-capture is responsible for most of the differences between how a lens "behaves" on an APS-C and a FF body. DoF, "safe" hand-holding speed, they're all the result of that post-capture enlargement.

JMHPhotography
4th of June 2006 (Sun), 13:22
Actually, that's not totally correct. ;)
The 18-55 kit lens is equivilent to a 28-90, which is a lens I used to have before I went on my buying binge of nothing but L glass, but that's another story. I tested that 28-90 on my 300D before I sold it, and it was wider than the kit lens on 18, and longer than the kit lens on 55.

You have a magical 28-90 then. I still have both lenses and I can tell you that there is NO way the 28mm end of the 28-90 is wider than the 18mm end of my 18-55mm. The other part about the 90mm end being longer than the 55mm end of the 18-55... well I guess all I can say to that is, 90mm being onger than 55mm is something you should expect.

lakiluno
4th of June 2006 (Sun), 13:29
I would agree with myself and everyone else. If your 28-90 gives wider results than the 18-55, then thats worrying.

If I can borrow my friends 28-90 in the next few days, I'll take comparison shots on my 350D and a tripod, to prove absolutely that what your saying is physically impossible...

cdifoto
4th of June 2006 (Sun), 13:51
Actually, that's not totally correct. ;)
The 18-55 kit lens is equivilent to a 28-90, which is a lens I used to have before I went on my buying binge of nothing but L glass, but that's another story. I tested that 28-90 on my 300D before I sold it, and it was wider than the kit lens on 18, and longer than the kit lens on 55.

I must have misread this the first time around. It's absurd either way I comprehended it though. lol.

blonde
4th of June 2006 (Sun), 13:57
I must have misread this the first time around. It's absurd either way I comprehended it though. lol.

don't worry, you are not the only one. i have been trying to understand what he is talking about but i can't understand it no matter what. its like saying that the 500mmL is shorter than my 400MM on the same camera...

cdifoto
4th of June 2006 (Sun), 14:01
don't worry, you are not the only one. i have been trying to understand what he is talking about but i can't understand it no matter what. its like saying that the 500mmL is shorter than my 400MM on the same camera...

Better yet....my 70-200mm f/2.8L has a more powerful burst of light than my 580EX. :rolleyes: :lol:

blonde
4th of June 2006 (Sun), 14:04
Better yet....my 70-200mm f/2.8L has a more powerful burst of light than my 580EX. :rolleyes: :lol:

that is alot better :)

basroil
4th of June 2006 (Sun), 14:06
that little difference in width isn't limited to effective ranges vs ff ranges. there was a test between three 17mm lenses (a sigma, tamron, and the ef-s 17-85IS), and the ef-s came out wider than the other two in the tests. the difference is almost nothing though, if you were talking about the difference between 14 and 18, then it may be bigger, but small changes become less noticible as focal length increases.

the ef-s 17-85mmIS is a great walk around lens when you want to take many different shots. if you like lenscapes, go for 17-40L (it's about $120 more, but that's money well spent). if you want some landscape but more people shots, the 28-135IS will probably be better to have. only issue against 17-85 is the strong CA and distortions at both ends, but mainly on wide end.

lakiluno
4th of June 2006 (Sun), 14:24
a lot of lenses aren't exact focal lengths, but they are within a mm or so, so its OK. 28vs 18 is obvious though :)

DocFrankenstein
4th of June 2006 (Sun), 14:31
It means the lens is an overpriced piece of poop. :)

Just an opinion ;)