Clarifiacation and help

I have been reading all of the post and comparisons that I can find on POTN about different lenses. Many of the reviews and comparisons of lenses that are in the sticky threads seem like they are way outdated. What I am looking for is a lense with a focal length of 17-28mm on the short end and around 50-75mm on the long end. F/2.8 is a must. I do not want a prime, and I do not want to spend the money on L glass (I love taking pictures, buy I love being frugal more).

So my choices appear to be:

Sigma 18-50mm f/2.8 EX DC Marco
Sigma 24-70mm f/2.8 EX DG
Sigma 28-70mm f/2.8 EX DG
Tamron SP AF17-50mm f/2.8 XR Di-II
Tamron SP AF28-75mm f/2.8 XR Di

First of all, Sigma says their DC lenses and Tamron says their Di/Di-II lenses are specifically built for dslr's with the smaller sensors. Does this mean that both of those styles of lenses act like the EF-S lenses and the 1.6 crop factor does not apply to the focal length of the lens? Hope that made sense.

Second, of the five listed, which one performs the best in regards to image quality throughout the focal range at f/2.8? I only ask about f2.8 because from all of the hours upon hours I spend reading on the wonderful site, it appears that most lenses will only get better stopped down in regards to IQ.

My primary concern is image quality (well obviously money is my ultimate concern since I will not ante up for an L). I don't really care about how quickly or silently it focuses. I don't really care if it cannot be used on a FF body, as I never intend on using a FF body. I just want to take great photos at a reasonble price.

If it matters, I am shooting with a 30D.

Thanks!!

Either of the Tamron lenses would be a good choice. I have the 28-75 and have a friend who owns the 17-50. Both are excellent lenses and aren't prohibitively expensive. The wider of the two is only for cameras with APS-C sensors.

So, only the Di-II lenses are APS-C specific? Not the Di? What about the Sigma DC?

I can only recommend the 24-70 since it is the only one I have in your list. Do a search for Fstopjojo who has done heaps of lens tests. Have a look also on fredmiranda.com for lens reviews.

HAve fun!

The Sigma DC and Tamron Di-II are built for the APS-C sensor. If they could be placed on a full-frame camera (I don't know if they will physically fit or not) because they are designed for the smaller sensor, severe vignetting would occur. When you say "the 1.6 crop factor does not apply", this is not correct. The crop factor refers to the sensor, not the lens. What it means is that the field of view obtained with a lens of a given focal length will, because of the smaller (than FF) sensor of your 30D, approximate the FOV of a lens whose focal length is 1.6 times as long on a full frame camera. There are several threads, at least one fairly recent, that explain this much more eloquently than I have, including visual aids.

As far as your prospective lenses are concerned, I have the Tamron 28-75 and highly recommend it.

Take a look here: http://www.the-digital-picture.com/Canon-Lenses/
They review every Canon lens and some Sigma and Tamron. I think all of the lenses you are looking at are reviewed.

It appears to me that between copy-to-copy on non-Canon lenses, quality differs a great deal. I was recommended the Sigma 24-70EX lens by many, but when I got it the quality was terrible.

It was superb build quality and a lovely lens to use, but focusing was slow, it was missing and had front/back focus problems. I know that I got a bad copy, but its put me off of 3rd party lenses for good.

Now I own a 28-105mm Canon and couldn't be happier with its quality. Along with that, over here in the UK its £100 cheaper than the 24-70EX!

All the related lenses looks to be almost enough good following all the posts you can see here.

I think you must narrow yourself at the point to say if you NEED the wide angle or not. If 17 mm is important to you or not; or you can go from 24-28 mm side. I beleive that´s the more important decission to you now, because you have a 1,6 crop factor body. After it, it will be more simplified.

I have a Sigma 24-70 f/2.8 EX DG that works pretty good, I am very happy with it, good IQ, so good copy. But not only this lens has had problems with focusing in some copies, lastly there are also a few threads in this forum about similar problems with the expensive and marvelous Canon 24-70 f/2.8 L (I can not affordt it in that price!!). Quality issues are in all brands.

Don´t miss the Sigma AF 17-70mm f/2.8-4.5 DC Macro although is not f/2.8 all the focals; but can address all the focal range you require, with good IQ & price as it has been reported.

Of those you mention I would consider the 24-70mm Ex and the 17-50mm Tamron. For general walkaround use the wider lens will be more useful. I had the Sigma and found it a good lens and only lacking at the 24mm end when I needed a wider angle. I have seen enough of the Tamron to know that is too. The longer Tamron I also had and the problem is 28mm doesn't do the job on a crop sensor in terms of wider angle usage. Personally, I now use the Sigma 17-70mm DC which has pretty much replaced my 17-40mm L as day to day walkaround. The 28-105mm Canon is also pretty good, but the problem is 28mm again if you don't have a wider angle lens.

I'm sure any of those lenses will do a great job. The shooter is the most important variable so there are plenty of terrible shots taken with them all too

runninmann wrote in post #2237794
The Sigma DC and Tamron Di-II are built for the APS-C sensor. If they could be placed on a full-frame camera (I don't know if they will physically fit or not) because they are designed for the smaller sensor, severe vignetting would occur. When you say "the 1.6 crop factor does not apply", this is not correct. The crop factor refers to the sensor, not the lens.

Sorry for not making myself more clear. I understand that the DC and the Di-II are built specifically for the APS-C sensor. I also understand that the crop factor of the sensor does not change by putting on a lense.

When I meant was, since those two series of lenses are specifically made for the APS-C sensor, are advertised focal lengths actually what you are getting on a APS-C sensor? I though (and maybe I am wrong) that the EF-S 18-55mm, truely is 18-55mm on an APS-C sensor (it is not a 28-88mm). Is this correct?

safehaven wrote in post #2239213
Sorry for not making myself more clear. I understand that the DC and the Di-II are built specifically for the APS-C sensor. I also understand that the crop factor of the sensor does not change by putting on a lense.

When I meant was, since those two series of lenses are specifically made for the APS-C sensor, are advertised focal lengths actually what you are getting on a APS-C sensor? I though (and maybe I am wrong) that the EF-S 18-55mm, truely is 18-55mm on an APS-C sensor (it is not a 28-88mm). Is this correct?

Every lens of a given focal length, whether EF-S or EF (or the 3rd party equivalents), provides the same focal length whether used on a crop camera or a full-frame. The difference is that the field of view is narrowed due to the smaller sensor upon which the image through the lens is projected. You don't get a longer focal length than that stated on the lens by using a crop camera. You get a narrower field of view that approximates the field of view of a lens 1.6 times longer on a full-frame camera. The image size is the same, at the same distance and focal length.

Alrighty...lets try this with some other lingo...

If you mount an EF 70-200mm f/4L to a body with an APS-C sensor, it "behaves" as though it is a 112-320mm lense, correct?

If you mount an EF-S 18-55mm to a body with an APS-C sensor, will it "behave" like an 18-55mm, or will it "behave" as though it is a 28-88mm?

If you mount an EF 70-200 on an APS-C sensor or a full-frame, it will have a focal length of 70-200. If you mount an EF-S 18-55mm on an APS-C sensor, it will have a focal length of 18-55mm. If you mount an EF 70-200 on an APS-C sensor, it will have a field of view equivalent to a 112-320mm lens on a full-frame sensor. The sensor will not "see" the full image that the lens projects. If you mount an EF-S 18-55 on an APS-C sensor, it will have the field of view equivalent to a 28-88mm lens on a full frame sensor. The difference is that the EF-S lens is constructed so that the sensor can "see" more of the image that the lens projects. Since it is designed for the smaller sensor, it can be made smaller.

http://www.kennymc.com​/crop-factor.htm

Juan Zas wrote in post #2241044
http://www.kennymc.com​/crop-factor.htm

Yep!