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02-04-2013, 12:59 PM   #1
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constant aperature or focal length?

What do you think is better to have, if you only had 1 main walk around lens?

I am deciding between tamron 17-50/2.8 or sigma 17-70/2.8-4.5

I'm thinking that the extra 20mm is better to have because I can always use a tripod- mostly low light stuff would be travelling, and in historic buildings etc. Most outside pictures, where I would probably be more likely to zoom in, & during the day would be ok at 4.5, handheld.

Is this correct thinking? What have your experiences been?

02-04-2013, 01:06 PM   #2
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The Tamron lens is going to give you much better IQ I would say. Overall I would also go for a 17-70mm because of its convenience, but I would wait for the new Sigma 17-70mm F2.8-4 C, which is going to deliver better IQ than the old version (plus it has HSM).

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02-04-2013, 01:07 PM   #3
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Constant aperture is usually a sign of a higher quality lens. Usually, not always. The question you have to ask is how often do you shoot wide open? I know I hardly ever do, the DOF is too small for what I am usually shooting. So if you are always shooting at f/5.6 then the cost of the f/2.8 lens is maybe not worth it?

So for me, assuming the image quality was the same, I would take focal length. But I prefer constant aperture lenses for the quality even though I rarely use them wide open. YMMV!
02-04-2013, 01:10 PM   #4
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one of the sad realities of variable aperture lenses is that they get slower, the longer you go, so when you really need perhaps more speed, you are giving up light twice, once for higher shutter speed to eliminate camera shake (although SR does help here to get some of this back) and the obvious loss of light by the reduction in F stop.

Having said that, most of the time when travelling, longer focal lengths are outside, so as you point out, many of these would be daylight situations where it does not matter,

the 70mm would be more useful than the 50mm top end of the tamron in my opinion

02-04-2013, 01:16 PM   #5
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I'd pick a 17-50/2.8 over a 17-70/2.8-4.5 any time.

20mm is important, but I can always crop.

In general, zoom lenses with constant aperture are built with tighter tolerance, and thus have better IQ at the same aperture.

Also, a lens's IQ is not at its best at max aperture. Normally, the best IQ is obtained at 1 or 2 stops from the max aperture.

At 50mm, the 17-70/2.8-4.5 is about 1 stop slower 17-50/2.8. Only one stop, but this is very important because it happens at the long end where you need higher shutter speed.

I happen to take a lot of flash photos, and tend to avoid p-TTL as much as possible. A lens with variable aperture is an additional headache that I don't need.

I don't know about you, but I don't count on having, or being able to use, a tripod.
02-04-2013, 01:21 PM   #6
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Didn't you already buy the 17-50? Are you having some buyer's remorse because it's not doing what you want it to?
02-04-2013, 01:35 PM   #7
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Nah, he probably has the LBA bug and wants justification to indulge... Hell, just go for it!! Though I don't think that extra 20mm at the long end will make much difference at all.
02-04-2013, 01:37 PM   #8
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QuoteOriginally posted by seventysixersfan Quote
Didn't you already buy the 17-50? Are you having some buyer's remorse because it's not doing what you want it to?
I did buy it but wonder if I rushed in without knowing enough. For the same price, i could get the new 17-70. Or for half the price ver 1 of the 17-70.

I'm a she, not he, and love to shop, but always second guess myself!


Last edited by PBandJ; 02-04-2013 at 01:38 PM. Reason: Gender mod...
02-04-2013, 01:55 PM   #9
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I'll be curious what you think. I have a Sigma 18-50 f/2.8 zoom that is pretty good but I admit that there are times I wished it zoomed out to 70mm to get tighter portraits. Plus I think the new 17-70 as well as ver 1 has fairly decent close focus / pseudo-macro ability at 70mm. Anyway, I have often thought about swapping out my f/2.8 constant zoom for a 17-70 range. But I also wonder how much I'll miss having f/2.8 at 50mm.

Here is the aperture range, by the way, of the Sigma 17-70s (copied from the in-depth reviews of these lenses on the PF)

Version 1
17 f/2.8
20 f/3.2
24 f/3.5
40 f/4
70 f/4.5

Version 2 (and presumably same as newest Contemporary version of 17-70)
17 f/2.8
23 f/3.2
34 f/3.5
70 f/4
02-04-2013, 01:59 PM   #10
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Since this is a walk around lens I would go for the 17-70, then stick a prime or 2 in your pocket (or purse) for low light and/or higher IQ.
In my experience, that 50-70mm comes in handy.
02-04-2013, 02:24 PM   #11
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Thank you for posting this table. i'm not really sure how to interpret it.

For example, at:
20 mm, it's a difference of 0.4 stops
30 mm --0.3 stops
50 mm-- 0.5 stops
Is it enough to really make a difference outside a lab? I don't know the answer. And I'm just making my first upgrade from a P&S.
I can post comparison pics if you like.

As for the LBA.. The 10-20 should be here this week, keeping fingers crossed. I'm hoping that the 10-20 will be my main walkabout. and I also got the 35mmDA/2.4 in the marketplace. So 3 lenses total.
And I caved and bought a camera bag.


QuoteOriginally posted by seventysixersfan Quote
I'll be curious what you think. I have a Sigma 18-50 f/2.8 zoom that is pretty good but I admit that there are times I wished it zoomed out to 70mm to get tighter portraits. Plus I think the new 17-70 as well as ver 1 has fairly decent close focus / pseudo-macro ability at 70mm. Anyway, I have often thought about swapping out my f/2.8 constant zoom for a 17-70 range. But I also wonder how much I'll miss having f/2.8 at 50mm.

Here is the aperture range, by the way, of the Sigma 17-70s (copied from the in-depth reviews of these lenses on the PF)

Version 1
17 f/2.8
20 f/3.2
24 f/3.5
40 f/4
70 f/4.5

Version 2 (and presumably same as newest Contemporary version of 17-70)
17 f/2.8
23 f/3.2
34 f/3.5
70 f/4
02-04-2013, 02:31 PM   #12
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QuoteOriginally posted by PBandJ Quote
Thank you for posting this table. i'm not really sure how to interpret it....
2.8 - 3.5: 0.5 stop
2.8 - 4.0: 1 stop
2.8 - 4.5: 1.5 stops

To make up for 1 stop loss, you'll have to either cut the shutter speed in half, or double the ISO setting.
02-04-2013, 02:41 PM   #13
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QuoteOriginally posted by PBandJ Quote
What do you think is better to have, if you only had 1 main walk around lens?

I am deciding between tamron 17-50/2.8 or sigma 17-70/2.8-4.5

I'm thinking that the extra 20mm is better to have because I can always use a tripod- mostly low light stuff would be travelling, and in historic buildings etc. Most outside pictures, where I would probably be more likely to zoom in, & during the day would be ok at 4.5, handheld.

Is this correct thinking? What have your experiences been?
I have the Tamron 17-50 constant 2.8, and it seems to remain permanently attached to the K-7. IQ is very good, and low light performance is noteworthy. I got it primarily for use at inside gatherings, parties, etc., and it has really ended lens changing, carrying two cameras around my neck, and low-light photo failures. The on-camera flash even works out pretty well at, say 35 mm up to 50 mm. So I would highly recommend this lens, depending of course on your specific needs. I do not need the extra 20mm for my specific applications, but if you are doing concerts or sports, the extra 20 mm could be very important, though still maybe too short for most sports situations. I am lucky to also have the Tammy 70--300mm for outside situations, so the two Tammy zooms together meet most of my needs.Good luck on making the best choice for your situation.
02-04-2013, 02:53 PM   #14
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QuoteOriginally posted by SOldBear Quote
2.8 - 3.5: 0.5 stop
2.8 - 4.0: 1 stop
2.8 - 4.5: 1.5 stops

To make up for 1 stop loss, you'll have to either cut the shutter speed in half, or double the ISO setting.
Thanks for the explanation. The difference between these 2 is more important than I thought!
02-04-2013, 03:09 PM   #15
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QuoteOriginally posted by PBandJ Quote
And I caved and bought a camera bag.
"Caved?" I started with 1 camera bag in 2010, then added 2 more in 2011, and last week added my 4th. It just depends on the situation of where I'm carrying my camera and how many lenses I want to take with me!
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