Caranx Loc: Atlanta

Very interesting data from all your testing Tom. Well done! It seems that there has to be some compromise when a zoom lens is designed. A 100-210mm lens would most likely not show as much variation as an 18-300mm superzoom. The physics involved wont allow you to get everything without giving up something.

BTW, I think Nikon just released such a beast: An 18-300mm DX lens. (so 300/18 = 16.7x) If any of you aquire this beauty, let us know about its behavior

Looking forward to reading Tamron's reply!

thg3 Loc: La Quinta, California

For what it's worth...

I have the Tamron 18-270 also and the Canon 18-55 & 55 - 250 kit lenses. At 18mm & about 5 feet, both lenses take the same picture (from a tripod).

At 250mm vs 270mm, the 250 is much closer (zoomed in)as your pics show. I took a pic at 270 with the Tamron and then switched to the Canon 250 and backed out until I had the same size pic as the 270. The Canon said 135mm (from about 6').

Pictures of the full "super" moon last year with 250mm vs this year with 270mm show that the 270mm produces a moon that is really close to 8% bigger which is what the difference between 250 & 270 should be.

Tamron, in their literature throws the word "macro" around a lot (not saying that the 18-270 is a macro) but with a min focal distance of 19.3 inches I thought that at 20" and 270mm I could probably see inside a bug...

The Canon 55-250mm has a min focusing distance of 3.6' so from 44", I took a pic of a yard stick with the Tamron at 270. Got 4-3/8" top of frame to bottom. The get the same 4-3/8" with the Canon, it was set at 116mm - a very long way from 270. With the Canon 250mm lens set at 250mm, the pic only shows 2-1/4" - almost 1/2 the size of the Tamron set at 270mm.

I'm going to ask Tamron for a comment and will report if I get any reply...

Tom[/quote]

Very interesting data from all your testing Tom. Well done! It seems that there has to be some compromise when a zoom lens is designed. A 100-210mm lens would most likely not show as much variation as an 18-300mm superzoom. The physics involved wont allow you to get everything without giving up something.

BTW, I think Nikon just released such a beast: An 18-300mm DX lens. (so 300/18 = 16.7x) If any of you aquire this beauty, let us know about its behavior

Looking forward to reading Tamron's reply![/quote]

So I sent Tamron a msg over the weekend and a reply was waiting for me this morning. Not bad service... I'm not sure I totally undertand the answer but at least I got one... I assume that the translation is that in a lens that goes from 18mm to 270mm, this is as good as it gets...

Here's the reply:

"Hi Tom,
This is not abnormal, because the lens's focal length is based on an infinite shooting distance and its angle of view during this sort of shooting at an infinite distance is the same as other telephoto lenses.

If internal focus (IF) is used as the wide optical system, then the shorter the shooting distance is, the lower the magnification for telephoto shooting becomes. The Tamron all-in-one zoom lens uses the IF method to reduce the shortest shooting distance. As the focal length includes wide angle, close-distance shooting at the telephoto end creates a wider angle of view than other telephoto lenses when the magnification is reduced."

Hope this makes sense to someone...

Tom

Caranx Loc: Atlanta

Hi Tom, Thanks for the post. It sounds like what was figured out on the forum: that the angle of view determines what's seen by the sensor at various distances.

As you and many others have said before on UHH, you have to choose the right glass for what you intend to shoot. A wide range zoom may be a great walkaround all-in-one tool, but if you are shooting close and need to be right there in the middle of the action, a medium to long zoom may be a better choice.

I've learned and understood so much in the past few days of this thread. Now I need to go get me a 70-210 or 100-300mm! Oh Oh, here comes a NAS attack! Thanks again.

thg3 Loc: La Quinta, California

Further to Tamron's reply... If you set the lens at 18mm and look thru the view finder as you turn the focus ring, the view stays very close to the same size. If you do the same at 270mm, you can see the size change drastically. The Canon 55-250mm also changes at 250mm but not as much.

toenee65

I just recently bought the Tamron 18-270 and the same thing has occured to me. The first thing I did when I bought it was to compare it to my kit lenses of 18-55 and 55-300. The Tamron when fully extended at 270 more or less equates to the Nikkon lens at 200, and I have no idea why. If I take a pic at 270 on the Tamron and 270 on the Nikkon the Nikkon reaches further, don't understand why. Also at 55mm, yes the Tamron is a bit wider but not that noticeable. I bought it because I wanted the 270mm reach.