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Old Dec 13, 2004, 8:57 PM   #1
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Hi,

I see that most Manufacturers are now selling dedicated DSLR lenses. Can someone tell me (or point me in the right direction) why you might want a lens specifically for a DSLR. I understand the reason & concept behind focal length conversion factor, but as I understand you just need to be aware of this when choosing the focal length. For example if I have a DSLR with a 1.5 focal length conversion factor & I by a film SLR lens of 70-200mm, then I can expect it to behave as a 105-300mm zoom lens. So other than having to do a few small calculations is there more to it than that? Are there compatibility issues or quality issues mating a DSLR with a film lens?

thanks Bryan. :?
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Old Dec 13, 2004, 9:12 PM   #2
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other than the focal length multiplication...unless i'm mistaken, any new film lens will be compatible to a dSLR...

i think older lenses might not work with the AF (manual focus should work though)

lol, hopefully someone that ACTUALLY knows what they're talking about will come along

Vito
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Old Dec 13, 2004, 10:28 PM   #3
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The only reason I know of to get a lens made for a DSLR is cost. Really wide angle lenses are expensive, but if you can take advantage of them being made for the smaller sensor you can make them smaller and cheaper. (I still think that they are too expensive, but that is another matter.)

Other than that, I can't think of another reason (with the lenses for digital that exist right now) to get one.

Eric
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Old Dec 13, 2004, 10:41 PM   #4
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Bryan,

dSLR lens are designed with smaller APS sized sensors(compared to 35 mm film) of most dSLRs in mind. This isn't as much an issue with long range tele-photo lenses, but can makea difference when usingwide angle lenses. Nikon and Olympus have decided to make a line of DX or DC sized lenses designed with the size ofAPS sized sensors in mind. Canon is taking the sameapproach with its S series lenses specifically designed for the DRebel and 20D. Another factor is something calledback focus that theAPS sized lens have an advantage when compared to regular sized lens, especially for wide angle lenses. I don't know that much about it, but I'm sure one of the more technical people here can weigh in with better explainations.

Bill
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Old Dec 13, 2004, 10:58 PM   #5
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Bill,

When you refer to 'back focus' is this the speed with which the camera can focus or the accuracy of focus tha is affected?

On a related question, some of thesenew DSLR specific lens no longer have an aperture ring. The logic being that this is done bythe camera.So what happens with the film SLR lenses (that have the aperture ring) used on a DSLR? Does the DSLR ignore theaperture setting on thelensin a PROGRAM or AUTO mode? And if using the DSLR in a MANUAL or APERTURE PRIORITY MODE, would set the aperture through the camera or on the lens ring?

Sorry for all the questions but I'm DSLR ignorant. I have in past (10 years ago) some experience with full manual film SLR cameras & I more recently bought a Canon A75, but that has just fuelled my interest in getting a DSLR.

thanks Bryan
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Old Dec 14, 2004, 8:42 AM   #6
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The crop factor of the DSLR cameras really is both a disadvantage and an advantage at the same time.

What you gain on the telephoto end of the focal length you lose at the wide angle. In fact because even 3mm can make such a big difference in wide angle lenses the 1.5 or 1.6 crop factor has a larger impact thenon telephoto lenses. I guess it depends on your preffered style of photography if this is good or bad news for you.

One positive thing to consider about the crop factor of DSLR camerasis that the sensor isn't making use of a large portion of the image circle a lens creates. Lenses always (as far as I know) tend tohave their best, sharpest and brightest image in the centre of the image circle the lens createsand quality will drop towards the edge of the image circlewith distortions, vignetting and soft focus occuring. These problemsare effectivelycropped out by the smallerdigital sensor givinga better quality, albeit "zoomed"image then a 35mm film camera might get from thesame lens. Now this shouldn't be a problem on higher quality "L-Glass" lenses, but it can mean some of the cheaper lenses performing acceptably for DSLR users that 35mm SLR users wouldn't consider using.

At the moment, appart from wide-angle focal lengths, I can't see the new DSLR-sized sensors being that usefull. The lenses are smaller but they are also quite expensive. There is also a fairly limited second-hand market for these lenses as only D-Rebel and 20D owners can use them (for now)whereas anybody with a Canon EF compatible camera can purchase or sella 35mm lens whether they have film or digital based cameras. This means cheaper prices for people using the 35mm lens format thanks to theeconomics of mass-production and a large buyers market.

I dunno, maybe i'm only making excuses because I have a Canon 10D and perhaps DSLR sized lenses really are the way to go. But for now there aren't enough DSLR-sized lenses and of those that are around they aren't cheap enough or significantly better to make me consider a change anytime soon.
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Old Dec 14, 2004, 8:45 AM   #7
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bryanj wrote:
Quote:
On a related question, some of these new DSLR specific lens no longer have an aperture ring. The logic being that this is done by the camera. So what happens with the film SLR lenses (that have the aperture ring) used on a DSLR? Does the DSLR ignore the aperture setting on the lens in a PROGRAM or AUTO mode? And if using the DSLR in a MANUAL or APERTURE PRIORITY MODE, would set the aperture through the camera or on the lens ring?
... Unless you owned some older Nikon lenses the aperture ring has long disappeared! :idea:

The aperture mode(s) is controlled from the camera dial on all EOS cameras (including film SLRs)
Even on older FD non-AF lenses the aperture ring is locked into the A position and the aperture was still controlled from the body...
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Old Dec 14, 2004, 8:59 AM   #8
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bryanj wrote:
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Bill,

When you refer to 'back focus' is this the speed with which the camera can focus or the accuracy of focus tha is affected?

On a related question, some of thesenew DSLR specific lens no longer have an aperture ring. The logic being that this is done bythe camera.So what happens with the film SLR lenses (that have the aperture ring) used on a DSLR? Does the DSLR ignore theaperture setting on thelensin a PROGRAM or AUTO mode? And if using the DSLR in a MANUAL or APERTURE PRIORITY MODE, would set the aperture through the camera or on the lens ring?

Sorry for all the questions but I'm DSLR ignorant. I have in past (10 years ago) some experience with full manual film SLR cameras & I more recently bought a Canon A75, but that has just fuelled my interest in getting a DSLR.

thanks Bryan
First, I believe dSLR lenses are useful because (1) they're smaller (2) they're lighter, and (3) they're cheaper than a comparable regular lens.

P.S. The "crop factor" of the dSLR lenses exists, sort of. As mentioned, the lens will focus all the light on the sensor, so nothing is "cropped" out of the frame. But the focal length numbers are not true 35mm equivalents. My 18-55 EF-S is not the equivalent of an 18-55mm on a 35mm camera, but rather those numbers multiplied by 1.6. As redundo mentions, there are disadvantages to that (because a lens is often the best in its center, and with a dSLR lens, you get the full frame of light). But, because it's designed for the smaller sensor, the lense is smaller, lighter, and cheaper too.

"Back focus" is a term for the lens's ability to stay in focus as the lens is zoomed out. In the video camera world, the best way to focus is "critical focus" that is, you zoom all the way into a subject and focus (easier to see the sharpest focus) and then when you zoom out, that subject will stay in focus (so long as the subject doesn't change distance from the camera). If a lens doesn't have a proper "back focus," then the trick doesn't work, that is, the focus will not remain the same as you zoom out from critical. Because the dSLR lenses are manufactured to cover the smaller sensors (and only the smaller sensors) the back focus would be more dead-on accurate.

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Old Dec 15, 2004, 11:45 PM   #9
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Lighter and smaller they are, but cheaper I wouldn't agree, just looking at Canons two offerings since the first 18-55 EF-s.

The 17-85 EF-s is way over-priced for what it is. At least the 10-22 is unique in offering a true ultra-wide view for 1.6 crop cameras. Even with that I would not buy an EF-s lens today. It limits you to never graduating up if/when the larger image sensored bodies come down to affordable prices. EF-s lenses won't even cover the field of view of a 1.3 crop body. If you feel the bigger sensored bodies will always be out of your price range, then I guess the EF-s lenses are worth it. Just remember, lenses are long term purchases, bodies today are not. 5 years ago a 6 megapixel body cost around $12,000. Who knows what you might be able to afford 5 years from now.
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Old Dec 16, 2004, 7:03 AM   #10
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Although controversial, some manufacturers indicate that they are now coating their lenses differently for those designed for Digital Cameras (the idea being that the sensors in Digital Cameras are more reflective compared to film, which can cause increased flare and ghosting).

For example, Sigma says this about their new 18-50mm f/2.8 EX DC lens:

Quote:
Super Multi Layer (SML) coating reduces flare and ghosting from which digital cameras tend to suffer.
http://www.sigmaphoto.com/html/pages/18_50_EX_DC.htm

I've seen some users comment that lenses from other manufacturers designed for Digital Cameras have less problems from flareon digital cameras, too. Of course,it could be that newer lens designs have better coatings anyway, regardless of whether or not they were designed for Digital Cameras.


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