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11-12-2008, 08:28 AM   #16
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QuoteOriginally posted by bc_the_path Quote
After reading about the sensor of the K20D "outresolving" some of the older lenses, I wonder which of the following candidate lenses would be a better selection (I already have DA* 50-135mm and love it very much):

- Sigma 17-70mm f/2.8-4.5 (Even though this is not an EX lens, it is the most likely candidate for me IF the K20D is not outresolving it).
- Sigma 18-50 mm f/2.8 EX DC Macro (A bit pricy for me)
- Tamron 17-50mm f/2.8 SP XR Di II LD Aspherical (no experience with Tamron)

I do not consider the two obvious candidates from Pentax:
- 17-70mm f/4 SDM (because it is f/4 & because I haven't seen enough reports about its performance)
- 16-50mm f/2.8 DA* (It is pricy and replacing a poor copy in my country is too much of a headache; too risky).

I know many members have the lens in question. I wonder if they are happy with it ON THE K20D.

Thanks...
I'm surprised your list doesn't include the DA 16-45mm. My research led me to choose it over the Sigma 17-70mm.

11-12-2008, 09:44 AM   #17
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QuoteOriginally posted by creampuff Quote
All Sigma 17-70s have a locking mechanism on the zoom ring to prevent the possibility of lens creep. On my copy I don't even need to use it as I don't have lens creep.
Not exactly. The zoom lock on the Sigma 17-70mm only locks in place at 17mm, when the lens barrel is retracted. This prevents lens creep when you're travelling around with, but not actually using the lens.
11-12-2008, 12:39 PM   #18
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QuoteOriginally posted by audiobomber Quote
I'm surprised your list doesn't include the DA 16-45mm. My research led me to choose it over the Sigma 17-70mm.
I bought the Pentax 16-45mm over the Sigma 17-70mm a couple of months ago but always wondered if I had done the right thing.
I managed to get a 17-70mm for a decent price from this forum a few weeks ago so bought it with a view to keeping the better lens.

I have to say ... the Sigma is the one going back up for sale.
11-12-2008, 04:31 PM   #19
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My 17-70 is quite creepy too!

11-12-2008, 04:54 PM   #20
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QuoteOriginally posted by pop4 Quote
Not exactly. The zoom lock on the Sigma 17-70mm only locks in place at 17mm, when the lens barrel is retracted. This prevents lens creep when you're travelling around with, but not actually using the lens.
Isn't that obvious? How can you use the zoom ring if the zoom lock is set, unless you only want to shoot only at 17mm? I think I know what I'm talking about.
11-12-2008, 05:11 PM   #21
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QuoteOriginally posted by Mike.P Quote
I bought the Pentax 16-45mm over the Sigma 17-70mm a couple of months ago but always wondered if I had done the right thing.
I managed to get a 17-70mm for a decent price from this forum a few weeks ago so bought it with a view to keeping the better lens.

I have to say ... the Sigma is the one going back up for sale.
After owning the DA 16-45mm and the Sigma 17-70mm, my preference is for the Sigma. It has a better range and the variable aperture is a minor issue. The Pentax has a more even sharpness across the frame but the Sigma is better in the centre sharpness. The Pentax has a slight edge in colour rendition but the Sigma is better in build quality. The Pentax has the very useful Quick Shift but it is hopeless when using on board flash at 16mm as the lens barrel extends fully at 16mm. The Sigma's lens barrel extends as you zoom to the long end, which is better in my opinion. The Pentax has a tendency to underexpose (at least on my copy), requiring EV compensation. No problems exposure wise for the Sigma. Given Sigma's reputation for batch variation, best to test before you buy. Both lenses have given me excellent pictures but I find the Sigma a little more versatile because of the focal range.
11-13-2008, 04:49 PM   #22
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I have been using the Sigma 17-70 for quite some time now. It is an excellent lens at the price point. I used it on my K100D Super and also on my K20D and it produces sharp, well exposed and colourful pictures all the time. Autofocus is fast and relatively quiet for a screw-drive. Flare is quite well controlled. CA is minimal. Resolution is very good. Colours are very good. Build quality is fair to good.

The only flaws I found are those already mentioned:
  1. lens barrel creep: happens very often on my copy, i use the lock switch religiously
  2. variable aperture: annoying sometimes when in manual mode
  3. sucks in dust: not well sealed so dust particles are easily sucked onto the internal elements

I have just upgraded to the Tamron 17-50 f2.8 but have not had chance to test properly yet so no real comment. The build quality is much higher on the Tamron, although the zoom/focus ring action is in reverse direction to the Sigma so that will take some getting used to.
11-14-2008, 01:05 AM   #23
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QuoteOriginally posted by creampuff Quote
Isn't that obvious? How can you use the zoom ring if the zoom lock is set, unless you only want to shoot only at 17mm? I think I know what I'm talking about.
Perhaps it's obvious to YOU, but not so to others, so I was just clarifying. I have the 17-70mm, so I know how it works, but when i think zoom lock, I also think of one what will work at all focal lengths.

Think of it this way, you've got the camera + lens on a tripod, shooting downwards, composed and focused at say 35mm. You want to minimised any camera shake/vibrations so use a wired-release/ delayed release, etc, and you take your hands away from the set-up. The lens then slowly creeps, and the focal length slowly increases; it's ruined the composition you had. But with an all-focal length zoom lock, you can lock it at the 35mm in this example, and it will stay at 35mm, or whatever focal length it's set at. Lens creep doesn't just occur at 17mm, and nor in one direction either; I set my 17-70mm at 70mm, point it upwards, and it'll creep back down towards 17mm.
And I'm damn sure I'm not the only one that thinks that way when 'zoom lock' is mentioned.

But, I digress....

11-14-2008, 01:48 AM   #24
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pop4, even the DA 18-250mm also has a zoom lock and it only works at one setting. Appreciate it if you can show me a modern zoom lens with a zoom lock that locks at all focal lengths. I'd be curious to see it.

If your Sigma's zoom ring is overly loose that the lens barrel creeps when pointed up or down, perhaps it may warrant a visit to a Sigma repair facility for a checkup. Alternatively, some gaffer tape may do the trick.
11-14-2008, 07:09 PM   #25
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The Sigma 17-70 has been the default for my camera since I bought it. Only time it comes off is when I need a prime to do some SERIOUS work. Great lens.
11-14-2008, 10:39 PM   #26
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I am surprised to hear the reports on lens creep with the 17-70. I have owned one for some time and have never experienced lens creep at all......... touch wood.
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