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02-15-2013, 10:19 AM   #16
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Both the Tamron and the Sigma that you link in the above post are similar in features.

The aperture is 2.8 on these lenses. That means that the widest the lens opens is 2.8. The smaller the number, the wider the lens opens to let in light. A fast lens is one with a large aperture. If you are taking pictures indoors or in low light, you generally want a faster lens.

The Sigma 17-70 isn't a constant 2.8 across it's entire range. Meaning at some focal points the widest it will open is 4. However this lens has further reach (ie. 70 versus 50).

02-15-2013, 10:27 AM   #17
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QuoteOriginally posted by civano Quote
The Sigma 17-70 isn't a constant 2.8 across it's entire range. Meaning at some focal points the widest it will open is 4.
Would that (f4) at short or long focal length?
02-15-2013, 10:39 AM   #18
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QuoteOriginally posted by moshepupkin Quote
Would that (f4) at short or long focal length?
I don't have the 17-70 but I'm assuming the 4 would be at the longer focal lengths. I'm not sure what the actual maximum aperture transition points are.

For my K-r, I started with the 18-55 kit lens and the 55-300 zoom. I found the 18-55 too slow indoors. I've got a Sigma 30mm 1.4 that I use indoors when I want to be able to for low light. However, I also found that I wanted a good walkabout lens with some length longer than 55mm so I also got a 18-135mm which I love when I don't want to switch around lenses and have good light or am outdoors. And because I wanted something faster with longer reach indoors taking pictures of my kids, I also picked up a Tamron 28-75 2.8 as a Valentine's Day gift from my hubby.
02-15-2013, 10:45 AM   #19
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I just found this on the 17-70 about aperture transitions doing a google search. I'm not sure if it is accurate or not as I don't have the lens. Hope it helps.

Flickr: Discussing Maximum Aperture Transition Points in The Sigma 17-70 f/2.8-4 DC MACRO OS

02-15-2013, 10:49 AM   #20
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BTW, how was I supposed to know (without asking you guys ) that 17-70 is not a constant f2.8? Still trying to figure out what would really be the limitations of this lens...

I've also noticed that there are 17-50 and 18-50... with 18-50 being MUCH cheaper... not that I'm looking for the cheapest lens possible, but just out of curiosity, what is wrong with this one?
02-15-2013, 10:58 AM   #21
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I don't think there is anything wrong with a cheaper lens per say but maybe this Adorama FAQ might better explain why some lenses are more expensive than others including the 17-50 versus the cheaper 18-50 (Sigma I assuming) you asked about.

FAQ: What does a more expensive lens really buy you? from Adorama Learning Center
02-15-2013, 11:23 AM   #22
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Thanks, that explains the difference between 17-50 and 18-50!

Back to 17-70 with non-constant aperture... what would be actual limitations of that lens compared to 17-50?
02-15-2013, 11:26 AM   #23
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QuoteOriginally posted by moshepupkin Quote

Back to 17-70 with non-constant aperture... what would be actual limitations of that lens compared to 17-50?
One thing is the lack of constant low aperture. It won't be as fast which matters when you are taking low light pictures or when you want a shallow depth of field.

02-15-2013, 11:44 AM   #24
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QuoteOriginally posted by moshepupkin Quote
BTW, how was I supposed to know (without asking you guys ) that 17-70 is not a constant f2.8?
First, I wrote that info in my post Second, it's called "17-70 f2.4-f4" so that tells you something :P
02-15-2013, 11:55 AM   #25
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If you like Tamron, a good lens to carry around all the time will be the Tamron 28-200mm. Gives you a lot of coverage ... more than you will probably ever need.
Autofocus seems OK (at least never had much of a problem with it).
02-15-2013, 12:10 PM   #26
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QuoteOriginally posted by mrNewt Quote
If you like Tamron, a good lens to carry around all the time will be the Tamron 28-200mm. Gives you a lot of coverage ... more than you will probably ever need.
Autofocus seems OK (at least never had much of a problem with it).
I hate Tamron Seriously, I had TERRIBLE autofocus problems. There were situations when the camera would not focus no matter what I did so I eventually would give up on that shot!
02-15-2013, 12:20 PM   #27
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QuoteOriginally posted by moshepupkin Quote
I hate Tamron Seriously, I had TERRIBLE autofocus problems. There were situations when the camera would not focus no matter what I did so I eventually would give up on that shot!


Than Pentax or Sigma lenses are the way to.
What now ... depends a lot on how much you want to cover and how much you want to spend .
A few good options were already recommended.
02-15-2013, 12:44 PM   #28
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Thanks for all the answers, BTW.

I think I'll get a Sigma f2.8 17-50.
02-15-2013, 01:28 PM   #29
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: Cool: Pentax DA17-70/4 , constant aperture, the ideal range, sharp open wide, constant sharpness throughout the range and breadth,silent fast focus , contrasting colors, charm lens for around constantly : P

Last edited by mbukal; 02-15-2013 at 01:35 PM.
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