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Let's say I shoot with Canon EF 35mm f/1.4L, Canon EF 50mm f/1.4, and a Canon EF 85mm f/1.8. Can these 3 primes be replaced with a Canon EF 24-70mm f/2.8 for the convenience of not needing to change lens so often?

Also I just wanna clarify that when I'm comparing image quality I'm talking about what can be actually be seen in a 10R print, I don't need a pixel by pixel comparison. In addition I'm just a amateur shooter, mainly shooting portraits and street, with some landscape, architecture, and random things lying around.

EDIT: I shoot with a 5D, so 24mm is enough for my wide-angle needs. Also I'll still be using the primes when I have a specific thing in mind to shoot. I just prefer to shoot light when walking around in the city or when I'm travelling.

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Changed the title so it's more directly related to what you asked, rather than what it was implying :) –  Alan Feb 1 '11 at 6:14
    
@Alan Thanks. :) –  jon2512chua Feb 1 '11 at 6:16
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It is so very worth it to carry 3 prime lenses around vs the 24-70L. The 24-70L is very not sharp at f2.8 and its much larger (physically) and heavier. You will miss the thin DoF, wide aperture shooting and lightness (of any individual lens) vs the 24-70L, not to mention the sharpness. –  Shizam Feb 1 '11 at 6:53
    
@shizam, @jon2512chua, the slrgear.com tests show that 24-70 lens is very sharp at f2.8. It softens slightly at 70mm but recovers its sharpness at F4.0(70mm). See this page at slrgear.com: slrgear.com/reviews/zproducts/canon24-70f28/tloader.htm –  labnut Apr 2 '11 at 6:41
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So many opinions but no facts. I have tried to supply the facts in my answer together with the references. –  labnut Apr 2 '11 at 7:30

6 Answers 6

up vote 11 down vote accepted

It depends heavily on what qualities in the final picture you care about. An f/2.8 lens won't simulate the depth of field of an f/1.4 lens -- ever. Even if the zoom was sharper, it still wouldn't give the shallow DoF of the f/1.4 primes. For portraits, that can (and often will) matter a lot. For landscapes, you'll typically use a fairly small aperture in any case so it's unlikely to make any real difference.

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1  
Good point. I forgot to take DoF into account. –  jon2512chua Feb 1 '11 at 6:50
    
I came in just to point out that you'd lack the ability to get as deep an OOF shot as a fast prime. –  Kendall Helmstetter Gelner Feb 1 '11 at 6:57

Prime lenses are usually faster (f/1.4 and f/1.8 from your lenses) which lets you shoot in extreme low light conditions. Using f/2.8 in same scenario might require you to bump ISO by 1 stop or two. If that's not a problem (You're using 5D which performs very well even with high ISOs), 24-70mm is the way to go.

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I'd say, based on your criteria, the answer is yes. However, the fact is, primes are usually a better option at a given focal length versus a zoom, a result of less complex optical construction. In terms of the lens range, it's good for portrait/street, but I think a little too long for landscape and architecture, though not terribly so, it rather depends on which Canon camera you actually have.

Now, despite all that, the big advantage of an SLR, beyond sensor size, is the ability to change lenses for the scene. Don't get too caught up in the idea of a "one size fits all" concept on your lens, it's a compromise versus a prime and will, in the long run, be something you'll see. Changing lenses isn't that hard, after all.

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I use a 5D. :) And yeah I understand that primes are better in general, but what I want to know is that is it that much better that it would justify me lugging around 3 lenses when walking around or travelling? –  jon2512chua Feb 1 '11 at 4:10

The OP asks ' I understand that primes are better in general, but what I want to know is that is it that much better that it would justify me lugging around 3 lenses when walking around or travelling?'

The quick answer, is no, if you use sharpness as your main criterion.

Slrgear.com measurements demonstrate that the loss in sharpness of the 24-70L zoom lens, when compared with the three primes lenses is relatively slight.

See these links for more details:
Sharpness of the 35mm f1.4
Sharpness of the 50mm f1.4
Sharpness of the 85mm f1.8 (no test results available for the f1.4)
Sharpness of the 24-70mm f2.8

To illustrate the point, below are extracts of the graphs from slrgear.com at f5.6. This aperture was chosen as this usually gives optimum results.

So what do you lose by using the 24-70 zoom lens?
1) a small loss in sharpness that will only be visible in photos where you require the very highest levels of sharpness, e.g. in very large prints.
2) the depth of field that f1.4 offers, probably not that important for travel and walk around photography. F2.8 is usually sufficient in these cases.
3) the prime lenses offer better contrast and clarity. This is a quantity difficult to measure. Once again the differences will only be visible in critical photography.

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Yes. There is the general consensus now that it is possible for a zoom lens to be equal or superior in quality to a prime, although some will contest of course ;)

Note the word possible. There are far too many factors to include either way in absolute terms. What you see now, is that a lot of professionals use zoom lenses for the majority of their shooting.

Whether it actually is needs to be determined in a case-by-case basis. Meaning you're going to have to do some homework to find out: Check MTF charts, read review and look at full-res samples.

For your particular example, I can tell you that the 24-70mm F/2.8 is extremely well regarded. I do not use it myself but several pro photographers I know do.

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Besides the DoF that most people talked about, for the sizes you will be printing, i really don't think you will be noticing a LOT of difference in image quality.

The 24-70 will have more chromatic aberration and such, being a zoom lens, but it's also a 1200$ Canon L lens, it certainly won't be rubbish.

And f2.8 gives a reasonably shallow DoF, it can be more than enough, if you use it well. And this goes to every lens: they all have limits, but when you get to know them and work around it, you get good (better:P) results!

I'd go for convenience and flexibility over sheer IQ everyday, especially for the range of hardware we're talking about.

OR, alternatively, go with just one prime and Cartier-Bresson'it. :D (this will probably be the cheapest solution)

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