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Old May 18, 2006, 8:56 AM   #1
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Moving from a Fuji S5100 (37-370mm focal length eqive) to a soon purchase of a 350D I need some lens advice. I realize I won't be able to get anywhere close to 370mm considering my budget for the inital purchases is around $1k. As such I will forgo the zoom for now. I don't want a Sigma or Tamron 18-200 due to the image quality compromises and slow lens speed. My lens budget is $400 USD (I can get the XT body only for about $580 USD)

As such I have narrowed my choice down to the follwoing to lens. Both of which are about $400

Sigma AF 17-70mm f 2.8-4.5 DC Macro
Sigma AF 18-50mm f 2.8 EX DC

Now, the 18-50 has better low light ability due to the constant 2.8 thru all zoom ranges.

Vignetting is highest at 18mm f2.8 @ 0.86 EV.

Worse MTF figures for 18mm f2.8 are: 1922.5 center, 1623.5 border, 1146 extreme border. Most all other combinations of focal length and aperture have higher resolution (peak appears to be 18mm, F8 @ 2066.5, 1784, and 1448.5.

Barel distortion is at about 2.13% @ 18mm, and all other focal lengths have minimal distortion.

CA is pretty bad at 18mm (fridges extend up to 2.5 pixels). 35mm is up to 1.9 pixls. Build quality considering it is an EX is very good.

Regarding the 17-70:

18mm is f2.8, 24mm is f3.2, 40mm is f4, and 70mm is f4.5. Thus it's low light isn't as useful at 40-70mm.

Vignetting is higher than the 18-50 at 18mm f2.8 = 1.19EV (the next highest is 0.65EV at 70mm f4.5).

Worse MTF figures for 18mm f2.8 are: 1776 center, 1456.5 border, 1184 exterme border. Most all other combinations of focal length and aperture have higher resolution. Peaks are at 18mm f5.6 having 2016, 1929.5, and 1807. Also 40mm f5.6 at 2019.5, and 1961 (no exterme border numbers for this one).

Barel distortion is at about 2.58% @18mm, 24-40mm distortions are low, 70mm pincusion is at about 0.6%.

CA is much better peaking at 1.31 @ f2.8 18mm. Second highest is 1.14 f4 18mm. Build quality is slightly less than the 18-50.

This lens has macro ability at 1:2.3 (basically half life size). Focus at 0.2 meters.

My questions:

I will be uses this lens on a trip to poland, germany, and france for a 12 day trip. As such the extra 20mm on the tele is very appealing to me. Sharpness between the two lens is pretty much a tie in my opinioin. 18-50mm is better at f2.8, but the 17-70 has a better sweet spot of max sharpness in the center, border, and exterme border combined.

Vignetting is similar on both but the worse is on the 17-70. CA is pretty bad on the 18-50 but much better on the 17-70. For more details about the two look at:


So which is better for a walk around lens? Which one will alow me to do more with photography?

Here are the things I'd like to do one day:

*landscape photos
*close up photos of flowers and such
*indoor family shots w/o flash
*possibly weddings
*action shots

I realize that just one lens probably won't let me do everything. I will eventually get more than one, but I am looking for the best OVERALL lens to start with. To me it seems to be the 17-70mm but does anyone think I should get the 18-50mm instead? If so why? Thanks in advance.

Lastly the 24-135 mm Sigma sounds appealing as it too is macro and 2.8-4.5. However I could not find any reviews about it (is it's macro the same as the 17-70?) Is is just as sharp as the 17-70 and 18-50 at 2.8? What about barel distorition? Is it comparable. In other words for it to be worth the trade of giving up the 17 or 18 wide ange for the longer telephoto It must preform just as good as the 17-70 or 18-50. If not then I'd rather get a sperate lens for telephoto work anway way. Like i said, I've probably narrowed it down to the 17-70 and 18-50 but I just wanted to make sure I wasn't missing out on something with the 24-135 as I will only be using one lens for this trip (as such more tele would be useful but I think I will miss the wide angle for shooting street scenes in paris, berlin, and poznan).

My priority is 1st image quality, then second lens speed, then third versitility. It isn't easy to decide which lens will be best as none will meet all three criteria equally.
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Old May 18, 2006, 9:45 AM   #2
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I went to sigmas sight and red a few more posts. I've also heard that the 24-70mm 2.8 EX DG is a good lens. Then I heard it has better contrast than the 18-50 EX DC? I still don't know which to get. There are so many choices. And remember image quality is my No. 1 priority with a $400 budget.

Below are the MTF charts for some of these lenses:

18-50mm 2.8 EX DC:

17-70mm F2.8-4.5 DC Macro:

24-135 F2.8-4.5:

24-70mm F2.8 EX DG:

I just wish the website that reviewed the 17-70 and 18-50 would do the 24-70 f2.8 as it's MTF chart looks impressive (remember 15 image height is all I should be concerned with on an 350D's sensor). I'd appreciate help in choicing here. Also is it wiser to buy full frame lenses instead of APS-C as regards furture investment? What about losing wideangle? Is that a problem on APS-C? Remember my shooting requirements as well as the fact my current camera (S5100) starts at 37mm so I've never go used to using wide angle.

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Old May 18, 2006, 9:51 AM   #3
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So I will reviese my request for which is best to:

18-50mm 2.8 EX DC
17-70mm F2.8-4.5 DC Macro
24-135mm F2.8-4.5
24-70mm F2.8 EX DG

Does anyone know of a webiste that has reviewed the later two so I can better compare them with the first two?

Right now, judging merely on the MTF chart, the 24-70mm F2.8 EX DG looks like a good lens. But it is missing the wide angle and Macro capabilities of the 17-70. Rememer my goal is a genreal purpose walk around lens that I can use almost everywhere except for when I need alot of reach (but I'll get a different lens for tele work).

It isn't easy to chose between these four. Just as it isn't easy to choice between the d50, d70s, and XT. But I chose XT for image quality and features ove the nikons even though they felt better and fit my hand better. I use a tripod and monopod most of the time so the XT's worse grip won't be as much an issue for me as I previously thought. Choices, choices, choices. This is hard!
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Old May 18, 2006, 10:15 AM   #4
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Here are the physical pics of the lenses:





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Old May 18, 2006, 3:34 PM   #5
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The 24-70mm F2.8 EX DG is actually much larger an heavier than theses scale indicate...

IMO if you have to pick 1 lens I'll go between the 18-50 or the 17-70 :idea:
-> 24mm is not wide enough and for the tele end you can always crop

Also FYI - http://www.pbase.com/lightrules/lenstests
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Old May 18, 2006, 4:01 PM   #6
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Is the 24-70 EX a better lens though? Image quality? what about 18-50 ex vs. 17-70? the copy the reviewers had of the 18-50 could have been a little soft?
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Old May 18, 2006, 8:48 PM   #7
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nelmr wrote:
Is the 24-70 EX a better lens though?
All EX are better of course - They are made out of metal (instead of composite/plastic) the lens is not only a constant f/2.8, but also a full-frame hence quite hefty however.
-> IMO you need more than 1 lens because 24mm is not wide enough on a 350D... on a 5D may be.

what about 18-50 ex vs. 17-70? the copy the reviewers had of the 18-50 could have been a little soft?
If it was me, I always go for the faster lens which is the 18-50 F/2.8 EX :-)
However IMO the 17-70 is much more flexible plus it has semi macro capability :idea:
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Old May 18, 2006, 10:10 PM   #8
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Thanks for the feedback. This isn't easy. I also found another review of the 18-50 and 17-70. THe 18-50 being EX prefermed very well and was one of the highest resolution lens the the reviewed has seen. http://www.ephotozine.com/articles/v...icle.cfm?id=70

This is his conclusion:

This lens is small for an f/2.8 model and although it suffers slightly at the wide-open aperture the focusing ability throughout the focal range warrants the aperture. From f/4 onwards it is a cracking lens that is light enough to have fitted to the camera permanently as a walk-round lens. It left me feeling that the extra price paid over the standard DC lens was well worth it. A highly recommended lens.

In summary the main positive points of the Sigma 18-50mm f/2.8 EX DC are:
Quick, accurate autofocus
Small and light for an f/2.8 lens
Sharpest lens tested to date
Useful protective pouch

Negative points are:
CA wide open
Slight distortions at either end (Minor point)

Regarding the 17-70:


In it's price bracket, this lens can be considered good. It's one drawback is the distortion at the wide end, but this is one of the easier problems to cure in digital software and being designed purely for digital cameras with cropped sensors will have no effect on film users. The DC/DG coating that Sigma now uses has gone a long way to improving their lens's contrast and this shows well in this example. The close focus ability of this offering also helps to greatly increase its versatility.

In summary, the positive points of the Sigma 17-70mm f/2.8-4.5 DC Macro are:
Excellent close focus ability
Good build with no wobbles
Good resolution figures overall

The negative points are:
Barrel distortion at the wide end
AF not as quiet as HSM lenses

Hmm... according to these reviews the 18-50 EX is sharper than the 17-70 but unlike the other reviewer in my first post he didn't test the extreme borders where the 17-70 outpreformed the 18-50. Nevertheless it does appear the 18-50 EX is a faster lens and has a usable 2.8 aperture.

But comparing the two this set of reviews shows the 17-70 to not be as sharp as the other review said. Could this be a difference in the copy of the lens?

They also had the 24-70 EX reviewed as well (non macro version):


This is a large lens that is well built and feels like it will go the distance. The zoom ring is surprisingly small for the size of the mechanism it has to move, but although a little heavy in operation, worked well. Autofocus is noisy but accurate. The 24mm end is just wide enough to start being call wide angle on a cropped sensor, but if you are still mixing digital with film, then this lens is a very good buy.

Picture quality, especially edges stopped down.
Build quality
Easy manual focus
Price (especially from ePz shop)

Noisy Autofocus
Big for range
A little soft wide open

Another favorable review quating resolution slightly higher than the 17-70 but less than the 18-50 EX.

I guess I really can't go two wrong with any of these three. I have to choose what to compromise and what is most important I guess (again it is very hard!!!).

17-70 has good overall resolution, contrast (slightly worse than the 18-50 though), and color. Has 1:2.3 macro capability and closs focus. Not to metion the highest zoom ratio. 2.8 only @17mm. Best CA preformance. Moderate to low vignetting. Compact and not too heavy.

18-50 EX seems to have excellent resolution, good contrast, and color. Poor macro. Smallest zoom ratio. Moderate to okay CA preformance. 2.8 all apertures. Low vignetting. Compact and not to heavy.

24-70 EX seems to have a resolution somewhere in between the 17-70 and 18-50 but with a little better contrast and good color. Has a mediocre macro preformance, but better than the 18-50 EX. Has just a little more zoom ratio than the 18-50 EX. Least amount of vignetting. Low CA. Has 82 mm filter thread ($$$). Looses wide angle on 1.6 crop. But can be used with full frame in the future. Very large and heavy.
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Old May 18, 2006, 10:23 PM   #9
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One more thing about the 17-70. I found this form a old post here on this forum. Someone plotted when it's max aperture changes with focal length:

f2.8 17mm

f3.2 17-26mm

f3.5 26-35mm

f4 35-50mm

f4.5 50mm+

As such it is only 1/2stop slower or lessthan the 18-50mm in the 17-34mm range. it is 1 stop slower in the 35-50 mm range. It seems to me that the 17-70 makes a decent indoor 17-34mm lens but allows me to do up to 70mm out doors not to mention semi-macro work. Is this a correct assumsion? Or am I kidding myself that I could use this lens at 17-34mm indoors?

As such how much does this limit my low light indoor ability (such as for weedings, gyms, parties, etc) with the350D? Does this mean that I will need ISO 1600 instead of 800? If so is that bad? This lens is still about a stop faster overal compared to a normal 3.5-4.5 lens it seems?Comments are welcome.

So I guess it boils down to this for me:

If the 17-70 can pull of low light (no flash) indoor photography at weddings and such at 17-34mm I will probably go for it sense it seems to give the most versitilty. If it can't then I see the added resolution and indoor ability of the 18-50 to be almost irresitable. But then again I will be uses the lens I choose on a 12 day trip to eroupe that probably will be a once in a liftime trip. So as such does anyone think I will miss any shots without the 50-70 mm range and lack of macro on the 18-50?

At this point I am beginning to rull out the 24-70mm I think. Again more feedback from other users (NHL you can keep commenting too if you like of course) would be appreciated. I am having a hard time choosing. I keep going back and forth and this time it seems to be between the 18-50 and 17-70. Thanks in advance for everyone's help.
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Old May 19, 2006, 2:18 AM   #10
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I'd go for the 18-50.

I personally don't fancy non-EX Sigma lenses, they feel cheap to me. Constant f2.8 is great, and the difference between 50 & 70 is only a step or two in most circumstances. Zoom with your feet and get the better lens.

This is going to be the lens on your camera most of the time, you might as well go for the quality.
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