Am I cheated?

[CanonShooter]

Hi,

Just wanna ask you guys about this...

I went to SimLim to buy a telephoto lens for my digi camera...
The shopowner told me it was a 2.5X lens so I bought it.

When I got home, I mount my camera on my tripod and shot an object at a fix distance with and without my 2.5X len at the same zoom...

When I compared the object height in term of pixels in PS, it turned out to be only about 1.38X the height...

Do you all think I have a case against them if I bring this to CASE?
OR should I go back to the store to clarify it?

Has anyone tested your telephoto lens in the same will? Will the magnification of the height be 2.5X or the same magnification as your telephoto lens if your camera and object distance is kept at the same place??

The brand of the lens is GroBartiG - Telephoto AF 2.5X
Please help/advice.

Regards,
Sim

[Winston]

Originally Posted by CanonShooter Hi, Just wanna ask you guys about this... I went to SimLim to buy a telephoto lens for my digi camera... The shopowner told me it was a 2.5X lens so I bought it. When I got home, I mount my camera on my tripod and shot an object at a fix distance with and without my 2.5X len at the same zoom... When I compared the object height in term of pixels in PS, it turned out to be only about 1.38X the height... Do you all think I have a case against them if I bring this to CASE? OR should I go back to the store to clarify it? Has anyone tested your telephoto lens in the same will? Will the magnification of the height be 2.5X or the same magnification as your telephoto lens if your camera and object distance is kept at the same place?? The brand of the lens is GroBartiG - Telephoto AF 2.5X Please help/advice. Regards, Sim

If the markings of the tele-converter did indicate 2.5x and it is not "re-marked" by the store than the shop did nothing wrong when they told you it is a 2.5x

Because they also got the information from the markings on the tele-converter.

Can only blame the maker for giving the wrong info.

[vince123123]

nevertheless u may still have a legal right to bring back to the shop for a refund as the item did not conform to its description.

Originally Posted by Winston If the markings of the tele-converter did indicate 2.5x and it is not "re-marked" by the store than the shop did nothing wrong when they told you it is a 2.5x Because they also got the information from the markings on the tele-converter. Can only blame the maker for giving the wrong info.

[mpenza]

it's meant for video cameras. try to bring back for refund/exchange. but avoid another teleconverter if you can. any of the easily available ones which is more than 2x will perform badly with cameras and do not perform to spec.

[ckiang]

Originally Posted by CanonShooter Hi, Just wanna ask you guys about this... I went to SimLim to buy a telephoto lens for my digi camera... The shopowner told me it was a 2.5X lens so I bought it. When I got home, I mount my camera on my tripod and shot an object at a fix distance with and without my 2.5X len at the same zoom... When I compared the object height in term of pixels in PS, it turned out to be only about 1.38X the height... Do you all think I have a case against them if I bring this to CASE? OR should I go back to the store to clarify it? Has anyone tested your telephoto lens in the same will? Will the magnification of the height be 2.5X or the same magnification as your telephoto lens if your camera and object distance is kept at the same place?? The brand of the lens is GroBartiG - Telephoto AF 2.5X Please help/advice. Regards, Sim

That's because you're only measuring one dimension.

If you shoot a 2x2m box and it appears in your final image as 200 x 200 pixels at 1x (no teleconvertor), adding a 2.5x will make that same box roughly 316 x 316 pixels ( sqrt( (200x200) x 2.5 ) ) and not 500 x 500 pixels.

i.e. it magnifies total area, not any single dimension.

In my example, the new height is therefore 1.58x the original. Your example works out to a magnification of about 1.9x. It's common to have teleconvertors performing less than its stated rating. Same goes for the actual focal length of lenses (i.e. 35mm might actually be 33 or 37mm).

Regards
CK

[CanonShooter]

Hi, for those interested in this thread.. I went back to the shop and explained to them my understanding of the teleconvertor.. and they gave me a full refund in cash.

Anyway, I saw a 3x TC at A photo.. when fixed onto my G2 the image height was close to 3x larger... at least 2.5x bigger.. but too bad there was the dark rings around the edges.. if not I sure buy!!!