Roger Hicks Loc: Aquitaine

This is, as you say, mind boggling. The focused distance should be measured from the sensor plane, so the fact than one lens is physically longer shouldn't matter. A faint possibility is that focal lengths are measured to infinity, and change drastically at close ranges, but I don't know enough about lens design to say more. Another possibility is that the focal lengths are not very realistically marked.

Just as a test, with the camera on a tripod and at a fixed distance from the subject, try shooting a yard stick with the two different lenses, at a range of marked focal lengths, to see what you get.

Cheers,

R.

SteveR Loc: Michigan

According to a review, the Di indicates that the lens is designed for use on crop sensors, which means that 270mm is all you get. With the Nikon you get the multiplication factor which gives you 300mm.

MT Shooter Loc: Montana

Sorry, but the Nikon is a DX lens also. Same format there.

Caranx Loc: Atlanta

Thanks Roger. I sort of did that with the flower shots when I adjusted the Tamron to 200mm to match the Nikon at 200mm. The discrepancy continues throughout the range to 55mm. I will do the test using a yardstick or tape and post the results later. Thanks a million.

Caranx Loc: Atlanta

True...but the D200 uses a APS-C sensor and both lenses were designed for that format so the multiplication factor should be the same. I have even wondered if the Tamron lens was mislabeled at the factory! I'll check out the same models of both lenses at the local camera store and post my findings / explanations later. Thanks for your help!

SteveR Loc: Michigan

Woulda been nice of the OP to include that little fact. He included everything else. I didn't see it until I pulled up the lens after your post MT.

Caranx Loc: Atlanta

Steve: not sure what OP means (hope its not "offensive photographer" lol) but I wrote the complete description of each lens in the initial post including that it was DiII glass. Sorry for any confusion. Thanks

Gibar

Hello all, after reading this post, and the owner of a Tamron 18-270. I had to try this out for myself,using the Canon 55–250 for comparison. there is no doubt that the Canon out reached the Tamron at all focal lengths, and now the question is why? maybe, it's the new math there using, or just marketing.

Caranx Loc: Atlanta

OK. Went to our local Showcase store and lo and behold there was a Tamron rep there preparing for a photography seminar Also on site was a certified Nikon repair tech with some 50 yrs experience, and several other reps. Problem solved! Well not so fast...both gentlemen examined the lenses, camera and took pictures and were just as perplexed as I was! Neither had an explanation nor had experienced this but agreed something was very wrong here. Bottom line is that I have been referred directly to the head of Tamron's service dept to have the lens evaluated. When I get the report I will share any findings for those who are interested.
Thank you thank you all for your help on this. I'll keep you posted.

MT Shooter Loc: Montana

Sounds like you definitely picked the right day to stop in and ask! Good luck.

SteveR Loc: Michigan

OP means original poster. You did not indicate that the Nikkor was DX. After MT's post I pulled up the full description of the lens and DX is part of the descriptive nomenclature of the lens. Without its inclusion I assumed it to be an FX lens. As Roger H would say...Cheers!!

SteveR Loc: Michigan

Is it possible that it has something to do with field of view? I don't know, I'm pulling rabbits out of a beret.

Caranx Loc: Atlanta

You are correct! I did'nt include the DX info on the Nikon... I was so focused on the Tamron! (bad pun). Talk about myopic vision. Sorry again and thanks for explaining OP. I'll learn the jargon as I grow with the forum. Cheers to you too. I owe you one!

Caranx Loc: Atlanta

Thanks MT. Glad I went by. I wish I could have caught the expressions of perplexity of each person that tried the lenses at the store! I will post the results hopefully in the near future. All the best.

SharpShooter Loc: NorCal

Steve, keep pulling rabbits out and forget photos, get a good job at Ringling Bros. Seriously, it will make no diff if the lens is set up for crop or FF. All that means is that the crop lens can be made cheaper by either having smaller diameter optics since the focus circle is smaller, hense less cost or they are not polished all the way out to the edges but they will still give the same magnification.
Since we've had three diff Tamron lenses do the same thing(including the reps) then it has to be the lens.
Is it possible that the manufacturer is the first to label the lens with the crop factor equivelent??
They could actually have the same physical length and be diff magnifications. Roger, MT and myself were involved a while back in a discussion where it was mentioned that what makes a telephoto a telephoto is the fact that it has a group of optics that are called a "telephoto Group". It is this group which enables a lens to be physically shorter than its' actual focal length, which all telephoto lenses are. I think if a company were to set this lens group up in a particular way it could very well control the actual length of a lens to be a shorter focal length and then label it as the same length as other lenses of the same physical size. It's a stretch since I really hope that the companies are not starting with such underhanded practices in order to compete in an already fiercely competitive market.
Lets hope that Caranx comes back with much better news and explanations than that.
But if so, remember you heard it here first, on the Hog.