Chefneil

I really want the Tameron 24-70 f2.0 lens. I used one and could make no bad shots with it. So I went to amazon to see what they had. Well, it turns out to be aroubd $1300 for new. http://www.amazon.com/Tamron-24-70mm-Canon-Mount-AFA007C-700/dp/B007SNP02K/ref=sr_1_1?ie=UTF8&qid=1423971684&sr=8-1&keywords=tamron+24-70+canon That just ain't gonna happen any time soon!

A little further down the page theyhad this, http://www.amazon.com/Tamron-28-75mm-Aspherical-Canon-Digital/dp/B0000A1G05/ref=sr_1_2?ie=UTF8&qid=1423971985&sr=8-2&keywords=tamron+24-70+canon. It is "aspherical" and a whole lot cheaper.

Does any one out there know what the difference is? and can you explain it?

wdross Loc: Castle Rock, Colorado

An aspherical lense is a lense with one or more lense elements that are not spheric. Most lense elements' surfaces are just part of a glass globe surface - spherical. This bends the light at the edge of the lense fairly strong. It also acts like a strong prism and breaks the light into a rainbow. This can require other glass corrections to bring that rainbow back into that single point of white light by the time it reaches the film or sensor. Most aspherical lense elements have a flatter outer surface than a spherical lense element. This keeps the rainbow from "spreading" as much at the edges and can make the correction easier along with the possibility of needing less elements for corrections. The better the lense correction, the less chromatic aberration at the edges of the picture frame. This can also be an extra cost, due to being harder to make, or save money, since less elements will be needed for the lense design.

MIKE GALLAGHER Loc: New Zealand

Pretty good description here.
http://en.wikipedia.org/wiki/Aspheric_lens

lamiaceae Loc: San Luis Obispo County, CA

Actually I don't think that answers his actual question. It just makes it more confusing. I think he was most concerned about the price. I don't think that the aspherical issue has anything to do with the price. Just different lenses. I don't get it either. Perhaps someone else sees why the huge price difference. But here is a graphic of the optics question.

Chefneil

Thanks for all of your input.

Well, I guess I am interested in the tech side of the question. But, mostly I am concerned with IQ. Is it the same as the standerd lens that costs 3 times as much? The whys are intersting, but cost and Image Quality are what matters to me.

Thanks for it!

CO

I've read that precision ground aspherical elements are very expensive to manufacture. The precision grinding process is time consuming. Most aspherical lens elements are moulded now. The moulding process is faster and much less expensive. Some have a plastic piece which has the aspherical shape that gets cemented to glass lens elements.

wdross Loc: Castle Rock, Colorado

Normally a lense costing three times more will have the better overall image quality. Is it worth three times more? That is the answer all of us must decide when buying a lense (unless you have unlimited funds). DPReview and SLRGear are two sites to see the lense reviews. Then, based off your shooting style and requirements, you will need to make the decision which lens to buy. From my own personal experience, if you are going to seriously continue in photography, buy the best lense possible without putting yourself even moderately in debt. It is even better for you if you don't put yourself in debt at all. That means one has to save the money for the lense - actual cash! In the pass, I have bought some of the cheaper lens. As I got better bodies, finer film, and now better sensors, sometimes the cheaper lense will not match up with the pictures one wants. Should you go broke getting the better lense? No. But most of us UHH want the absolute best pictures. That can mean breaking into a very large piggybank.

mcveed Loc: Kelowna, British Columbia (between trips)

The 24-70 has image stabilization, the 28-75 doesn't. The 24-70 is larger and heavier and has more glass. The front element is 82mm vs 67 for the 28-75. The 24-70 has a higher DXO score - see link. The difference in diameter of front element is significant, that and the VC capability accounts for the difference in price. In addition, the IQ on the 24-70 is higher.
http://www.dxomark.com/Lenses/Compare/Side-by-side/Tamron-SP-24-70mm-F28-Di-VC-USD-Canon-on-Canon-EOS-5D-Mark-II-versus-SP-AF28-75mm-f-2.8-XR-Di-LD-Aspherical-IF-Canon-on-Canon-EOS-1Ds-Mark-III___884_483_297_436

amfoto1 Loc: San Jose, Calif. USA

This is correct.

Also, the more expensive 24-70 Tamron has USD focus drive, which is much faster and more accurate, but adds to the price.

All in all, the $1300 Tamron lens is a much higher quality lens and will give much better performance and results than the older, cheaper 28-75 model.

Compare the Tamron to the Canon 24-70/2.8L II that sells for around $1900, the $1300 Tamron lens will seem like a bargain. The Canon lens doesn't have image stabilization (IS in Canon, VC in Tamron) either.

You also might note that these are f2.8 lenses (not f2.0 as stated in your original post). These f2.8 are pretty large & heavy, but an f2.0 24-70 would be downright massive and a whole lot more expensive than any of these.

Would you consider used? I see the Tamron 24-70 VC USD selling for around $850 used. Or the Canon 24-70/2.8L f2.8 USM first version, which can be found for around $900 or a little less.

I see you are using a crop sensor camera. Unless you are planning to trade that in on a full frame camera, and considering the other lenses you list (EF-S 18-55 and EF-S 55-250) instead of a 24-70, you might want to look at the EF-S 17-55/2.8 IS USM. It's not an L-series, but is a very high quality lens none-the-less. The EF-S 17-55mm sells for under $900 brand new or around $650 used. This lens will rival any of the 24-70's for image quality, offers the same large aperture, and it's focal length range could be a better fit for a crop sensor camera and your particular kit of lenses. The EW-83J lens hood for it is sold separately (and highly recommended), Canon's own is a pretty ridiculous $50, but there are cheaper third party hoods for $10-15.

Note: I'm pretty sure your lens list in your signature actually is: EF 50/1.8 II, EF-S 18-55, EF-S 55-250.

Don't know which you have, but the Mark II versions of the two EF-S zooms are pretty good optically. Even better are the STM versions of each of these, with improved autofocus performance (quieter, faster, smoother stepper motor, vs micro motor), non-rotating front elements (makes using polarizing filters a whole lot easier), 7-blade apertures (up from 6-blade, makes for nicer background blur), and some other refinements. They cost more, but not a whole lot more... about $50 per lens. These are all still "kit lenses", but the newer and especially the STM versions might be an improvement.

The 17-55mm, Tamron 24-70 and Canon 24-70s with much larger f2.8 non-variable aperture, USM or USD focus drive (even better than STM for fast action shooting) and their build quality are a big step up from kit lenses.