Rob909 Loc: Orland, Ca.

Hi, I'm Rob. I just joined and am really enjoying the site. Lots of nice people here!
I just purchased a Tamron 18-270 f/3.5-6.3 DI ii PZD as an upgrade for the Canon EF-S 55-250mm f/4-5.6 IS ii lens for my 70D. I purchased it used from B&H.
In the two photos I have attached, the first is the Canon zoomed out to 250, and the 2nd is the Tamron zoomed out to 270. Do I have a defective lens? Thanks for any input.

Canon at 250mm


Tamron at 270mm

Apaflo Loc: Anchorage, Alaska

The lenses seem to be just fine, but different.

Focal lengths marked on a lens are when focused at infinity. Different optical designs will be different when focused at shorter distances, particularly at less than 10 meters. Try the same comparison focused at 100 meters and there won't be much difference at the same focal length.

Don't be too critical, because generally losing focal length when close focusing also means being able to focus closer and with higher magnification. Just another design decision...

SteveR Loc: Michigan

There is something called "breathing" that can affect the effective focal length of the lens. The newest Nikon 70-200mm suffers from this.

mikeroetex Loc: Lafayette, LA

I assume you are not asking about sharpness, but the "zoomed" comparable size of subject.
Looks to me like you were using an FX type lens on a Crop sensor previously and the Tamron is a DX lens, designed for Crop sensor. Take another shot with Canon lens backed off to about 167mm and see if field of view doesn't match up better.

Granted, I'm a Nikon guy, so not totally familiar with Canon lenses, but I draw these conclusions from these manufacturer descriptions:
Canon: This high zoom ratio lens is equivalent to a focal length of 88-400mm in the 35mm format (when used on Canon EOS cameras compatible with EF-S lenses)....
Tamron: ...next generation 18-270mm, the world’s lightest, smallest 15x zoom optimized for use on APS-C- DSLRs.....

I reserve the right to be incorrect and have my math backwards!

Doowopa Loc: Connecticut

Had the same question when I got mine.
check my link



http://www.uglyhedgehog.com/t-270952-1.html

PixelStan77 Loc: Vermont/Chicago

Welcome. You got your answer. Enjoy your new lens.

mwsilvers Loc: Central New Jersey

No, your lens is fine. Zoom lens focal ranges are based at shooting at infinity. Take a picture of something close in at 18 and then at 270 and you'll immediate see that at 270mm the image is nowhere near 15 times closer than at 18mm. At infinity though, it will be. Try shooting at something in the distance and you'll find the image from the 18-270 will be slightly closer than the 55-250. This is a common phenomenon of zoom lenses.if you take another picture 10 or 15:feet farther out from the ones you posted above, the images may or may not be close in size, but the difference will likely not be as extreme. Depending on the goals you had for buying this lens, this can sometimes be an unexpected and frustrating artifact.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

I think you will find that you'll see less of this behavior as the distances increase. This is focus breathing, and internal focusing lenses (which don't change length when you focus) tend to be more susceptible to this. It is not a problem, just a characteristic and a lens design decision.

You can read up on it here:

http://www.bobatkins.com/photography/technical/focus_breathing_focal_length_changes.html

http://www.bythom.com/nikkor-70-200-VR-II-lens.htm

Marionsho Loc: Kansas

Welcome to the Hog, Rob909.

amfoto1 Loc: San Jose, Calif. USA

Welcome!

But, no, your lens doesn't appear faulty. It is "focus breathing", as noted in other responses. The Tamron essentially "changes focal length" when focused closer. Apparently quite a lot.

A clue to this is in the lens specs... The best the Tamron can do is .26X magnification, while the Canon lens can do .31X.

This doesn't necessarily indicate good or bad quality. For example, the Canon 100mm macro lenses are very high quality and they are IF (internal focusing) lenses that do something similar. When focused to their closest 1:1 magnification, their "true" focal length becomes something closer to 70mm, instead of 100mm. Not that it matters in use. You wouldn't notice it unless you put it beside another lens.

But, frankly I'm not sure I'd call the Tamron 18-270mm an "upgrade" over the Canon EF-S 55-250mm, which is a pretty decent lens in its own right. For one thing, as you've discovered, the EF-S lens gives higher magnification at it's closest focusing distance.

"All in one" 15X (and more) lenses like the Tamron typically have to compromise in other ways. Sure, they're convenient because you can do all your shooting without ever changing a lens... But, hey, that's one of the main points of a DSLR, that you can change lenses to adapt the camera for different purposes.

In general, the "best" zooms optically are those that are 2X, 3X to 5X, 6X or slightly more. You can see this by looking at the premium and most highly rated zooms: 10-22mm, 16-35mm, 17-55mm, 24-70mm, 70-200mm, 100-400mm, 200-400mm. 15-85mm, 18-135mm and 70-300mm are about the upper limit, IMO.



P.S. Not to worry.... Canon EF-S and Tamron Di II lenses are both designed specifically for crop sensor cameras such as your 70D (i.e., "DX" in Nikon-speak). Not that it matters... since your camera can fully use both crop-only and full frame ("FX" in Nikon-speak) lenses without concern. It also is completely irrelevant because 270mm is 270mm, regardless whether the lens is designed for and attached to a crop camera or designed for and attached to a full frame camera.

John_F Loc: Minneapolis, MN

Lenses have a set of cardinal points and planes. One set is the Principal planes - these are where from where object and image distances are measured. With zoom lenses whose focal length variability is acheived from movable front, rear elements, it is possible to have rear Principal planes that are not equally distant from the sensor plane. This could account for the difference in the two photos.

speters Loc: Grangeville/Idaho

The manufacturers stated focal length's for zooms are most times not accurate, its more like : it should be in around that ballpark. Tamron should have provided a lens spec sheet with it and in there is should state the actual focal length of the lens! One example, the Sigma 50-500 (it sells a lot better than if they would have put the actual focal length of 68-432 in their advertising)!!!

ebbote Loc: Hockley, Texas

Welcome to the Hog Rob, it looks good to me.

mikeroetex Loc: Lafayette, LA

Thanks, I learned something new today!

mwsilvers Loc: Central New Jersey

By the way, as others have mentioned, the Tamron 18-270 is not really an "upgrade" to your 55-250. This is not so say it's a bad lens, but superzooms in general, because of the complexity of their designs, are an optical compromise. They tend to be less sharp on the long end, less sharp at the edges, and have more distortion than lenses with smaller zoom ranges and prime lenses. The popularity of superzooms is strictly due to its convenience factor, which for many adds a lot of value. The results with you 55-250 kit lens will be as good as, and probably better than, the Tamron within that same range. But that doesn't mean you won't be happy with yours. I gave my copy of the Tamron 18-270 to my son when I started shooting with better lenses, and he loves it.