18-200mm or 18-50mm?

[TheMikeGuy]

Right now, for my T2i, I have the choice to buy one of these two lenses:

Sigma 18-200mm f/3.5-6.3 DC Aspherical (IF) Lens

Sigma 18-50mm f/2.8-4.5 lens

These are the only lenses I can afford, for I don't have a job.

Anyway, right now, I am working with both photography and video, and I'm just wondering what lens would work the best for those purposes. I already have a Canon 50mm f1.8 and a Rokinon 8mm lens.

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[Garbz]

Quality or convenience? The Sigma 18-200mm is a bad performer. All 18-200mm are but the Sigma takes it a bit worse. You'll have very horrible barrel distortion, lack of sharpness, and yay f/6.3 on the long end.

If you can have one lens only for a travel trip the 18-200 would be a consideration (still not necessarily a must), but in my opinion for general purpose standard / wide angle photography stay away from the superzooms.

[Timoris]

I have to say the compleat opposit,

I have the Sigma 18-200mm HSM OS f/3.5 variation

It is my new favorite lens.

Sharp at 200mm? - Check
Fast Focus on AF? - Check
Chromatic Aberrations? - Nope
Optical Stabilization? - Check
Macro? - Check
Amazing amount of Use with it? - Check.

There is some distortion at 18mm, but that's normal, it is wide angle.

[Garbz]

... You need to get yourself some decent glass.

I do agree though it is an incredibly useful lens.

And no 1:4 magnification ratio does not come close to what is considered "macro"

[Timoris]

This is true. However, being able to focus 47cm away whole being at 200mm, I find pretty useful. Infact, I even manged to get the AF set at around hqlf that distance. It may not be 1:1 but it is shweet.

[subscuck]

Chromatic Aberrations? - Nope

Seems those who test lenses for a living disagree...

At 18mm there's red/blue fringing at a level fairly average for this type of lens, and at 200mm some green/magenta fringing (although noticeably less than on competing lenses). All in all pretty good for a superzoom.

And another one...

At 18mm average CA performance is noticeable - 4/100ths of a percent of frame height - but it's the maximum value that concerns us most, at 9/100ths of a percent of frame height.

And since three is a magic number...

The CA characteristics of this lens are in-line with the other currently available super zooms.

It was also noted AF was dodgey @ 200mm due to the aperture, and while sharp at 200mm, competing lenses are sharper.

[Timoris]

Well of course you will get some CA, but not extensive diabolical CA with previous superzooms. Like the Canon 300mm USM one.

I have to say I hardly notice it, almost not present in many pictures.

Which site did you quote?

[subscuck]

Which site did you quote?

One is from dpreview, one from the digital picture and I don't remember where the third is from. I did a quick google search because I found it hard to believe, as you stated, that a superzoom would have no CA.

[Timoris]

Well yes, I did say that and you are right. However when posting I meant more to the effect of "negligable". Reading back, I am not even certain we are talking about the same lens as there are several Sigma 18-200mm.

[Garbz]

They all have field relevant CA.

Actually in the 18-200's defense, the 18-50 has far higher levels of CA:

This is clearly the weakest characteristic of the AF 18-50mm f/2.8EX - CAs (red/blue color shadows at harsh contrast transitions) are very high peaking in an average pixel width beyond 2 pixels @ 18mm. However, they're also quite strong occurrences throughout the rest of the range.

Justified quite well on the 18-200s by saying:

However, the situation isn't quite as extreme as with some other (even higher priced) lenses and actually pretty acceptable for such an extreme zoom lens.

[Joshonator]

It's pretty simple. Do you need a focal range longer than 50mm? Get the 18-200. If not get the 18-50. If you care more about better pictures than bigger zoom I would go with the 18-50 for the larger aperture alone.

Will you miss more shots by not having the 50-200mm availible or by not having a slightly larger aperture?

[Timoris]

Do you have a f/1.8 prime lens? If I only had two lenses it would be my cheapo (yet surprising) f/1.8 and either a kit or zoom lens.

Are we making you nervous? :p

[Terry Leach]

Strangly enough, I was very recently faced with this dilemma with the very same lenses. I, myself, decided that picture quality was far more important to me than large focals. Most of the time, I find that I can simply move closer to the subject and retain good quality rather than going to a longer lens. I went with the 50mm and so far seem to like it quite well.