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Old Apr 20, 2005, 7:44 PM   #1
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I currently own the following equipment (1 month):

Canon 20D
Canon EF-S 10-22mm F3.5-4.5 USM
Canon EF-S 17-85mm F4-5.6 IS USM
Canon EF 50mm F1.8 II
Canon 580EX


I'm now looking for a telephoto zoom lens. When talking to my local camera store rep, he referred me to the http://www.Photozone.de web site. Looking at the lens rating on this web site, I noticed that lenses do not have the same rating when comparing film and digital. For example, for film the Canon EF 70-200 F2.8L USM rates as the best lens (when listing lenses by performance) but for digital (APS-C DSLR) the Canon EF 70-200mm F4.0L USM rates as the best lens.
Why is there a difference between film and digital? :?
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Old Apr 21, 2005, 4:40 AM   #2
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I'm just learning about DSLRs (getting my first one in a fortnight). From what I understand though the difference is due to the difference in size between exposed film and an exposed sensor (film is larger than a CMOS sensor). So for a lens to be good is should have no distortions in the corners of the picture but a digital sensor uses a smaller area so a "lesser" quality lens would work because the distortions should be outside the corners of the digital sensor (while the same lens on a film SLR would show up). Probably also an additional factor also related is that the lesser surface area could mean the lens keeps a smaller f stop at all ranges with (or for longer) than a film back would allow.

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Old Apr 21, 2005, 11:40 AM   #3
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pelmen wrote:
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Probably also an additional factor also related is that the lesser surface area could mean the lens keeps a smaller f stop at all ranges with (or for longer) than a film back would allow.
Unfortunately not the case. The f-stop of a lense is the same regardless of whether or not it is on a film or digital camera. The mechanics that drive f-stop are all in the lense - so switching the body does not enable the lense to change it's aperture capabilities.

style="BACKGROUND-COLOR: #000000"But I would think the other argument holds some water. A lense that may have slight vignetting or distortion at the edges on a film camera might not have them on a smaller sensor since that sensor doesn't 'see' the outer edges anyway.
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Old Apr 24, 2005, 2:16 PM   #4
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Don't believe photozone.de. What is their grade anyway? I have yet to see their lab results which are broader than the two number figure.
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Old May 4, 2005, 1:49 PM   #5
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agiaccio wrote:
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I currently own the following equipment (1 month):

Canon 20D
Canon EF-S 10-22mm F3.5-4.5 USM
Canon EF-S 17-85mm F4-5.6 IS USM
Canon EF 50mm F1.8 II
Canon 580EX


I'm now looking for a telephoto zoom lens. When talking to my local camera store rep, he referred me to the http://www.Photozone.de web site. Looking at the lens rating on this web site, I noticed that lenses do not have the same rating when comparing film and digital. For example, for film the Canon EF 70-200 F2.8L USM rates as the best lens (when listing lenses by performance) but for digital (APS-C DSLR) the Canon EF 70-200mm F4.0L USM rates as the best lens.
Why is there a difference between film and digital? :?
When it comes to digital SLR's - especially the new camera's - high resolution sensors are less forgiving for optical quality of the lens than film was. They capture a lot more detail than the film plane did. So now, the optical quality of the lens has to be improved to match the quality of the sensor - which as you can see from the different manufacturer's who are coming out with the Di or Dx or Dg lens designations - are attempting to do.

You are off to a good start with the D-SLR and the lenses you have. Don't base your requirements for meeting your lens/photographic needs on photozone's reviews. Read the reviews so you see someone else's view on the equipment but no more.

The 70-200 f2.8L is just as good, if not better, than the 70-200 f4L with the additional f-stop you gain. The IS version of the 70-200 f2.8L is an excellent lens. What you need to see is if the $1600+ price of the f2.8L is more acceptable to you than the less than $700 price of the 70-200 f4L. I own the 70-200 F4L and I bought it after I sold the 70-200 f2.8L. I only sold the f2.8L so I could get a wider focal range - a 17-40 F4L and the 70-200 F4L (a lower cost alternative to make up the focal range I lost). The 70-200 F4L probably rates as the best lens only because it delivers excellent sharpness and truly remarkable quality fully open for a lens in that price range. I would highly recommend the 70-200 F4L as it is compact, light (by canon's "L" zoom standards), and probably the best bang for the buck when it comes to an "L" lens.


What you do loose with the F4L over the F2.8L is the ability to AF using teleconverters (rectified by using tape on pins) and the one f-stop mentioned above. Is the one stop really worth the weight and price of the f2.8.. that's up to you.


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Old May 4, 2005, 7:15 PM   #6
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pascal03 wrote:
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What you do loose with the F4L over the F2.8L is the ability to AF using teleconverters (rectified by using tape on pins) and the one f-stop mentioned above. Is the one stop really worth the weight and price of the f2.8.. that's up to you.

I learned this early. An extra f stop menas nothing when you dont need it on the other hand when you need the extra stop and dont have it now it is worth its weight in gold.
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Old May 4, 2005, 7:55 PM   #7
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The new Canon digitals deliver pretty clean images up to ISO3200.

In the good old film days you'd be hard pressed to use filmwith a sensitivity greaterthan ISO800 and still get a clean result.

Also, you can "push" your digital image's brightness and contrast a stop or two in post-production.

In the good old film days you could "push" a roll by a stop or two without knowing the outcome until you got your prints/proofs back.

Therefore, the new high ISO Canon digitals and post-production software gives you a reliable2-3 stop advantage over the old film days.

Therefore, an F/4 or even F/5.6 lens on a digital gives you as much to work withas an old film camera with an F/2.8 lens.

Having said all that, having an extra stop at the wide end never hurt, but it isn't as critical as it used to be.

-- Terry
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Old May 4, 2005, 7:57 PM   #8
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Keep in mind that the Photozone rating are based on user reviews, not lab data. The database is useful for getting an overview of lens quality but it's not absolute. Deviations will occur as a result of user inputs and a sufficient number of inputs. The Canon 70-200L series lenses are all fantastic. The difference in their MTF charts is just about nil. Get the 2.8 if you need a faster lens, get the 4 if you prefer light weight. (1.5lbs vs. 2.9lbs)
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Old May 4, 2005, 8:09 PM   #9
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You guys miss the most critical point - Most folks opt for the heavier f/2.8 not because of the faster speed, but because of the nicer defocus called 'Bokeh' in full daylight
http://homepages.ihug.com.au/~parsog/Guy/bokeh.html

This is what set an image apart from the slower lenses and has nothing to do with ISO! :idea:
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Old May 4, 2005, 9:21 PM   #10
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I always thought the quality of the bokeh was due to a 6-blade versus 8-blade aperture, nothing to do with the speed of the lens.
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