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01-17-2010, 04:24 AM   #16
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Yes the Tamron 17-50 gives you a constant aperture of 2.8 throughout the zoom range of 17 to 50mm..

QuoteOriginally posted by crossing Quote
Tamron 17-50mm i see on dppreview ''fast standard zoom lenses with an F/2.8 maximum aperture throughout the entire zoom range used exclusively for digital SLR cameras with APS-C sized image sensors'' , so on my k-x will have 2.8 all over zoom range ? If so ..order is already made for this one !


01-17-2010, 04:40 AM   #17
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Sigma 18-50mm/F2.8-4.5 DC OS HSM (not macro ) http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3359&navigator=6 - didn't have aperture of 2.8 throughout the zoom range? I dont find info abaut it over internet.

Last edited by crossing; 01-17-2010 at 07:19 AM.
01-17-2010, 05:37 AM   #18
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QuoteOriginally posted by crossing Quote
so on my k-x will have 2.8 all over zoom range ? If so ..order is already made for this one !
Yes it will have 2.8 at all apertures
01-17-2010, 07:33 AM   #19
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Sigma 18-50mm/F2.8-4.5 DC OS HSM (not macro ) http://www.sigmaphoto.com/lenses/len...59&navigator=6 - didn't have aperture of 2.8 throughout the zoom range? I dont find info abaut it over internet.

01-17-2010, 12:22 PM   #20
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QuoteQuote:
Crossing: Right !

So you hardly recomanda Tamron 17-50 f2.8 because the price its worth it altho more expensive then 18-50 Sigma. Can someone tell me f2.8 focal lenght for those 2 lens ? 17-70 i understand f2.8 its only at 17mm.

Also you think its a just a caprice to go for this lens instead of stick to kit 18-55 ? My needs as told here does not require this aproach ?
"Crossing," I cannot make out what you are trying to say in your above comments. I do not think you understood my original post to your thread. I was simply trying to suggest you compare pictures taken with the Tamron and Sigma to each other, and decide, for yourself, if the price difference is justified. I bought the Tamron 17-50mm, almost 2 years ago, and love it. I have no desire to replace it with anything else. It has nice colors & contrast, with excellent sharpness, even wide open. It close focuses nicely, has a 6-year warranty, and comes with a hood. Here is a shot with it @ f 3.2, 1/25th, ISO 200---Painted Trillium

Last edited by Jewelltrail; 01-31-2010 at 10:49 PM.
01-17-2010, 12:37 PM   #21
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Crossing, the only variable aperture zoom is the Sigma 17-70.
The others are f/2.8 constant throughout the focal range.
The Tamron 17-50 still trumps the others in image quality.
01-17-2010, 02:30 PM   #22
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QuoteOriginally posted by crossing Quote
Sigma 18-50mm/F2.8-4.5 DC OS HSM (not macro ) Sigma - Lenses - didn't have aperture of 2.8 throughout the zoom range?
No! When it says f/2.8 - f/4.5, that's exactly what it means - it's only f/2.8 at the wide end, but a maximum f/4.5 at the long end. That informatio is right there in the name of the lens as you posted it. There is a different Sigma lens that is f/2.8 through the entire rang,e and it is clearly label f/2.8 as opposed to f/2.8 - f/4.5.
01-17-2010, 03:15 PM   #23
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QuoteOriginally posted by Marc Sabatella Quote
No! When it says f/2.8 - f/4.5, that's exactly what it means - it's only f/2.8 at the wide end, but a maximum f/4.5 at the long end. That informatio is right there in the name of the lens as you posted it. There is a different Sigma lens that is f/2.8 through the entire rang,e and it is clearly label f/2.8 as opposed to f/2.8 - f/4.5.
Then 17-50 f2.8 its fixed ?.


Here is a shot with it @ f 3.2, 1/25th, ISO 200---Painted Trillium

How you made that one if aperture cant be modified ?

Sorry for stupid qestions and long theard for a simple thing..


Last edited by crossing; 01-17-2010 at 03:29 PM.
01-17-2010, 03:42 PM   #24
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QuoteOriginally posted by crossing Quote
Now I got... then 17-50 f2.8 its not for me. I dont shot only in low light , I need it also for landscapes, outside pictures.. f2.8 I think its more for low light..
Well, f/2.8 is useful for at least two things: low light, and shallower depth of field (nice sometimes in portraits and many other types of photos).

But let's be clear about something: A zoom lens with a fixed aperture throughout its range isn't ipso facto superior to one with a variable aperture, especially if you consider other qualities of the lens like zoom range and price. There are some fixed aperture zoom lenses out there that are only so-so as far as image quality goes, while there are quite a few variable aperture zoom lenses (including the Sigma 17-70 f/2.8-45 DC) that have rather good image quality. I wish my Sigma 17-70 f/2.8-4.5 were a fixed f/2.8, like the Tamron 28-75 or 17-50 lenses. But notice that the Sigma has a wider zoom range than either of the Tamron lenses, and it costs less, too. I wish my Pentax 18-250 were a fixed f/1.8 throughout its zoom range, but nobody to my knowledge makes such a lens and if they did it would cost $20K.

Not everybody needs the advantages of a fixed-aperture lenses at all, and even those of us who need those advantages sometimes, don't need 'em all the time. Indeed, I dare say that MOST photographers don't care about having fixed aperture lenses, most of the time. If they did, then kit lenses would have fixed apertures - but they don't.

What's the advantage of a fixed aperture - like you get on the Tamron 17-50 f/2.8, or the Tamron 28-75 f/2.8, or the Pentax 16-45 f/4, and many others? The main advantage is that, if you're shooting in low light, at the limits of the camera's capabilities, if you can manage an acceptable exposure at one focal length, you can zoom in or out to a different focal length without having to change your camera's settings (or without having them changed for you automatically). For example, if you're shooting in a dark church, and, at a focal length of 20mm, f/2.8 + 1/30th sec + ISO 1600 gives you a just barely acceptable exposure - if the lens has a fixed aperture, you can zoom in tighter on the subject safely, without having to worry that you're now going to be taking a grossly underexposed shot.

But most users do NOT shoot a lot in such difficult circumstances, and for a good reason. It's hard to get a good photo in bad light! Most users, most of the time, either shoot in fairly decent light - quite frequently outdoors during the daytime - or are able to use flash or some other form of supplementary light.

Now, the advantage I described above is pretty much the only advantage of a fixed aperture zoom lens. You can zoom without changing your exposure settings. That's it. Note that, when you zoom, even keeping the aperture constant, your depth of field is going to change, because, well, because depth of field is directly and intimately related to distance from the focal point of the photo.

Anyway, the bottom line is, if you aren't facing fairly extreme exposure + zooming challenges on a regular basis, then you may not give a darn whether your lens has a fixed aperture or not. The best thing we can all do to improve our photos is get better light on the subjects. And if you can shoot in better light, then having the aperture narrow to f/4.5 when you zoom in tighter may not matter much to you. I go over to the Dallas Arboretum to take some photos quite often. Sometimes I have a bride or a portrait subject with me. In that case, I probably don't grab a zoom lens at all: I grab a couple primes. But if I'm going just to enjoy the scenery and take some shots for fun, I probably grab a zoom, and the Sigma 17-70 f/2.8-4.5 is one that I'm likely to grab, because it's a good lens, and versatile. Most of the time when I'm at the Arboretum, it's daytime and the light is very good.

I'm not KNOCKING fixed-aperture zoom lenses. Just trying to counter the possible misunderstanding that they are somehow inherently better for all photographers. 'Tain't true.

Will
01-17-2010, 04:03 PM   #25
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QuoteOriginally posted by crossing Quote
Then 17-50 f2.8 its fixed ?.


Here is a shot with it @ f 3.2, 1/25th, ISO 200---Painted Trillium

How you made that one if aperture cant be modified ?

Sorry for stupid qestions and long theard for a simple thing..
Tamron 17-50mm f2.8 : not fixed, f2.8 is max aperture for entire range 17-50mm

Sigma 18-50mm/F2.8-4.5 : max aperture at 18mm is f2.8, and max aperture at 50mm is f4.5
01-17-2010, 04:05 PM   #26
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QuoteOriginally posted by crossing Quote
Then 17-50 f2.8 its fixed ?.


Here is a shot with it @ f 3.2, 1/25th, ISO 200---Painted Trillium

How you made that one if aperture cant be modified ?

Sorry for stupid qestions and long theard for a simple thing..
OK, in case you missed this little bit of info, when we say 'fixed aperture zoom' we don't mean that for example the 17-50 is f/2.8 throughout its focal range - we mean that the 17-50 has a MAXIMUM aperture of f/2.8 throughout its focal range.

Sorry for the confusion - this is wrongly assumed knowledge a lot of us don't consider, but I hope this makes it clearer. The maximum aperture value is one important figure to look at when looking for a suitable lens as Will says, but all these lenses can be 'stopped down' (i.e. decreased in aperture, or increased in aperture number if you will) to a maximum of between f/22 and f/32 (mostly).

See here for more information:
https://www.pentaxforums.com/forums/photography-articles/62522-exposure-shutt...rture-iso.html
01-17-2010, 06:28 PM   #27
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I am trying to just stick to your needs here: this is your thread. I will do my best to avoid all the digressions which have ensued.

QuoteQuote:
Crossing: I like photos in low light, thats why I buy it Fa 50MM 1.4 so the light...can get in...enough !
Okay, one clear thing to emerge from this thread is you do value a larger aperture in your prospective new lens and, in fact, that is your main reason for upgrading from the kit. One thing which has not been made clear in this thread yet is that larger aperture lenses cost more money than their smaller aperture counterparts. You could employ the analogy of buying a car here. One car has AC and the other one does not. All things being equal, the car with AC is more money. Do you use the AC all the time--absolutely not! Is it nice to have the AC in the heat of a hot summer--absolutely yes. Are you willing to pay the extra cash for the added benefit of AC? Well, that depends on you, your personal ability to deal with heat and where in the world you live. Someone in Alaska is not likely to put as high a value on AC as someone living in Miami, Florida. In much the same way, some photographers will put a higher value on larger apertures than will other photographers--it is that simple.
Therefore, no one here can tell you for sure what the best lens is for you to buy. You need to decide this for yourself. This is a great forum, full of helpful people, but you must be as clear as possible about what it is you want. Towards this end, you can educate yourself thoroughly on the subject matter at hand. You can borrow a book from the library, or study on-line but I would not recommend you buy anything until you are confident in your own knowledge on the subject matter--this way you can ensure your own satisfaction with your purchase.
Now, if you want the luxury of a constant aperture @ f 2.8, throughout the focal lengths of 17 or 18mm to 50mm to replace your kit lens then look at all available options within your budget. If you know for a fact you do not want a variable aperture lens, then rule all of them out and make the decision easy. Something else has not clearly emerged form all this discussion: Sigma makes an 18-50 f 2.8 constant aperture lens and it is in the price range of the Tamron 17-50mm f 2.8 lens. If you have established a constant 2.8 is what you want, then why don't you just narrow your decision to these 2 lenses? Read the reviews on both lenses which can be found all over the Internet, and look at all the pics posted for the 2 lenses. Best of Luck to you, "Crossing"

Click on this for starters:

https://www.pentaxforums.com/userreviews/showproduct.php?product=333&cat=74

Last edited by Jewelltrail; 01-17-2010 at 08:11 PM. Reason: add a link
01-18-2010, 01:25 AM   #28
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If f2.8 its not fixed ,whats the aperture range on 17-50 TAMRON ?
01-18-2010, 02:22 AM   #29
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How about some research. I typed 'tamron 17-50' in a search engine and one of the first hits is Tamron 17-50mm f/2.8 XR Di II Lens Review. If that's the lens that you're looking for, this is the spec page associated with the review.

To help you out (from that spec):
QuoteQuote:
Aperture Range - Wide / Long f/2.8-32
01-18-2010, 02:26 AM   #30
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QuoteOriginally posted by crossing Quote
If f2.8 its not fixed ,whats the aperture range on 17-50 TAMRON ?
at all focal length from 17-50mm
you can choose f2.8 up to f22
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