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Old Jul 12, 2010, 6:27 PM   #1
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Default 3 lenses 1 choice

hello
i am contemplating all purpose lens for matters of convenience
canon 18-200mm is lens
sigma 18-250mm os lens
tamron 18-270mm vr lens
so far i have tested the sigma at the henrys camera show, and with the umbrella flash i got pretty darn good portraits of the model on hand
will try and post pic but have to resize first
any comments
thanks in advance
pete
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Old Jul 12, 2010, 6:32 PM   #2
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I like the tamron 18-270mm. It is gives good results also for a megazoom lens. And the 20mm on the long end makes it a bit better all purpose lens.
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Old Jul 12, 2010, 7:38 PM   #3
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The Canon is shorter. (Duh!)

The Canon has more vignetting. You'll have to stop down an already dim lens to get around it.

The Sigma has slightly less distortion. If you'll be shooting at buildings, it will do a better job.

They all have a lot of chromatic aberration, so high contrast images will suffer.

None is particularly sharp wide open, or even sharper than the others at a range of focal lengths, but stopped down two stops, they're all reasonably sharp. (That would also take you out of the range where the Canon vignettes, btw.) But they're already pretty dim.

The Sigma is heaviest; the Tamron is lightest.
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Old Jul 12, 2010, 10:11 PM   #4
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thank you kind sirs
but stopped down two stops
what does really mean
i have probably done this unknowingly
but a technical explanation would be fab
oh shoot here is the data for the sample below

canon xsi/sigma 18-250mm os lens / f/5.6 /1/125 sec / iso 200 /
focal length 147mm / remote triggered umbrella flash / open space variable outside light
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Old Jul 12, 2010, 10:17 PM   #5
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stop down is the aperture. On your shot, it was taken at f5.6. If you make the aperture smaller say F8. The image would be sharper.
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Old Jul 12, 2010, 10:32 PM   #6
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PS

between the tamron and the sigma, at the same ranges, the tamron is brighter. The sigma at 250mm is at 6.3, the tamron at the same range is at 5.6 if I remember correctly.
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Old Jul 13, 2010, 4:03 AM   #7
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I own the Sigma 18-250 OS HSM in combination with the EOS 500D/T1i for a few days now - so far I'm really pleased with the shots I get... but I have to get used to the weight
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Old Jul 13, 2010, 6:18 AM   #8
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All the lenses you mentioned have small maximum apertures, and at those maximum apertures, they're not very sharp. In order to get sharp photos, you need to use apertures that are two stops smaller (i.e.: f/11 instead of f/5.6, f/13 instead of f/6.3.) In order to make up for the smaller apertures necessary to get sharp images, you'll have to use slower shutter speeds, risking motion blur, or higher ISO settings, risking image noise. If all you'll ever use it for is shooting outdoors, this shouldn't be a problem.

But another consideration is that at about f/15, the T1i reaches its diffraction limit. That is, as you stop down a lens (any lens) smaller than f/15, the image starts getting less and less sharp. So between stopping down two stops from the lens' maximum aperture, and staying above f/15, you don't really have much room to maneuver.
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Old Jul 13, 2010, 8:34 PM   #9
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thank you all kindly for your advice and comments
i know i will have to sacrifice but sometimes i need the shot
will have to think this one long and hard
i have till oct nov to decide that when the next henrys camera show will be hosted and hopefully there will be a price drop and some deals
cheers
enjoy summer and all its photo ops
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