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12-17-2011, 05:17 PM   #1
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Need help finding a lense

I am looking for a 50-200mm F2.8 or better at 50mm as well as at 200mm. I have seen F4-5.6, if the F stop changes when the focal length changes, then the lens is no good to me. Is there a lens out there. I will be willing to have a lens with different focal lengths, but the F stop must stay constant. Is the 50-135 have an F 2.8 apature at 135mm as it does at 50mm?


Last edited by dndcdr; 12-17-2011 at 05:24 PM.
12-17-2011, 05:34 PM   #2
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Yes, the Pentax-DA* 50-135mm F2.8 ED [IF] SDM is constant f/2.8 maximum throughout its focal range. It is also well-liked and expensive. See the reviews here: Pentax-DA* 50-135mm F2.8 ED [IF] SDM Reviews
12-17-2011, 05:37 PM   #3
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Thanks, money is not a problem. How about the Sigma or the Tamaron 50-200mm? Is the apature constant at 2.8 on thise lenses?
12-17-2011, 05:43 PM   #4
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Sigma makes a 70-200 that is constant f/2.8. Their 50-200 is not. They also make a 24-70 constant f/2.8.

12-17-2011, 05:48 PM   #5
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Sigma do a 50-150 constant f/2.8, which is quite good but you can only buy it used now as its dis-continued.
12-17-2011, 07:34 PM   #6
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If the aperture is listed as simply f/2.8 in the description, then it's f/2.8 throughout the zoom range. Variable maximum aperture zooms would be listed as f/2.8-4/4 or whatever.

General rule of thumb for telephoto zooms if you don't see the maximum aperture info in the specs for some reason:

If the zoom range is only 3X (longest focal length is three times the shortest), and it costs the better part of $1000 and/or weighs around two pounds, it's constant f/2.8. Otherwise - if the zoom range is over 3X, the costs is well under $1000, and/or it weighs well under two pounds - then it's not f/2.8 anywhere.
12-18-2011, 03:42 AM   #7
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Thanks, I will look at the Pentax 50-135 and the Sigma 70-200mm. I may end up getting both
12-18-2011, 03:50 AM   #8
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Tamron 70-200/2.8, thought it does not cover 50mm, it 's great thought the range at f2.8 compared to all other lenses I tried (50-135 & Sigma 70-200mm, both a bit soft at longer end wide open).

12-18-2011, 04:43 AM   #9
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Any reason why you insist on a constant aperture? Just curious.
12-18-2011, 06:26 AM   #10
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your shutter speed will change when you zoom in and you gro from F2.8 to 3.5. I am shooting basketball games and volleyball. I need the shutter to be as fast as possible at any focal length. I usually use fixed focal lengths but for sports, I think a zoom may be better. Why not have a lens that is a 2.8 at any focal length anyway?
12-18-2011, 10:32 AM   #11
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QuoteOriginally posted by dndcdr Quote
your shutter speed will change when you zoom in and you gro from F2.8 to 3.5. I am shooting basketball games and volleyball. I need the shutter to be as fast as possible at any focal length. I usually use fixed focal lengths but for sports, I think a zoom may be better. Why not have a lens that is a 2.8 at any focal length anyway?
cost/weight/size just to name a few
12-18-2011, 12:17 PM   #12
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QuoteOriginally posted by dndcdr Quote
your shutter speed will change when you zoom in and you gro from F2.8 to 3.5. I am shooting basketball games and volleyball. I need the shutter to be as fast as possible at any focal length.
You don't need a constant aperture for that, though - you just need to use an exposure mode that adjusts shutter speed automatically as aperture changes. Which is to say, any mode but M. Of couse, M is the only mode I normally shoot, so I too don't like using variable aperture zooms in any situation where I don't have time to keep hitting the green button to set shutter speed. But I'd have no problem switching to Av for sports shooting if it meant saving a ton of money and weight.
12-18-2011, 03:19 PM   #13
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You can fix your shutter speed by using Tv

Or set your aperture to f/5.6; but if the K10D in your profile is still your camera, I would indeed prefer a fast lens and they are usually constant aperture. Two stops at the long end will make the world of difference (e.g. DA50-200/4-5.6 vs 70-200/2.8).

The disadvantage of constant aperture zoom: cost, size and weight But I will indeed opt for a zoom.
12-18-2011, 03:48 PM   #14
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Thanks for the info. I am upgrading to the k-5 and getting a zoom lens. I am leaning towards the 70-200mm f2.8 Tammie
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