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??

Please help/advice.

Regards,
Sim

 

[darrelchia]

I'm not an expert in this area, so anyone feel free to correct me ... but i always assumed that when they say its a 2x magnification, it doesn't mean that the length is doubled, but the area is doubled. Mathematically, if you double the lenghts and widths, the area is quadrupled .. understand where i'm going ??

e.g example, for an square with 4, the area would be 16 ... if you double the area, it would be 32 (length 5.656.....), but if you double its lengths ... 8x8=64 .... making it 4 times magnification ...

of course, this is just a logical assumption on my part, as i'm not too sure about how they actually rate the magnification factors.

 

[mpenza]

the logical assumption is not correct.

anyway, it's not the shop's fault. The manufacturer is the one who's labelling the teleconverter 2.5x, not the shop, who is only a reseller. Try to bring it back and see if you could exchange for something else. Also, the teleconverter you have is meant for video cameras and not digital cameras and might really work like a 2.5x teleconverter on video cameras.

 

[vince123123]

If im not wrong, 2.5x refers to the multiplier factor on your current "mm" of lens.
for eg if your lens is 10-100 (arbitrarily chosen to illustrate), the 2.5 will make it 25-250. u may want to take a picture at say, 100mm without the convertor, and then put on the covertor and take a picture with ur camera set at 40mm, giving an effective 100mm lens when used with the convertor. then compare the two pictures.

cheers

 

[ST1100]

Conventionally, the 2.5x refers to the focal length. Ie if your lens was 50mm, it is now a 125mm.

The correct way to do the 'pixel check' is this:

Find out what is the angle of view (or field of view - FOV) between the two lenses. Use trigo (similar triangles) to determine should be the magnification of a straight line from the original to the 2.5x. That would be the correct 'pixel increase' in your image.

i haven't calculated it - might be 1.38x, might be 2.5x. i don't know.

 

[wacko]

I'm not an expert in this area, so anyone feel free to correct me ... but i always assumed that when they say its a 2x magnification, it doesn't mean that the length is doubled, but the area is doubled. Mathematically, if you double the lenghts and widths, the area is quadrupled .. understand where i'm going ??

e.g example, for an square with 4, the area would be 16 ... if you double the area, it would be 32 (length 5.656.....), but if you double its lengths ... 8x8=64 .... making it 4 times magnification ...

of course, this is just a logical assumption on my part, as i'm not too sure about how they actually rate the magnification factors.

sorry to say but this is totally wrong. focal length is directly proportional to image size.

 

[yowch]

the logical assumption is not correct.

anyway, it's not the shop's fault. The manufacturer is the one who's labelling the teleconverter 2.5x, not the shop, who is only a reseller. Try to bring it back and see if you could exchange for something else. Also, the teleconverter you have is meant for video cameras and not digital cameras and might really work like a 2.5x teleconverter on video cameras.

Yup, the label is often 'jacked' up to improve sales. And the reseller can always claim that you should have tested before buying and that he only told you what was obviously printed on the lens.

I have seen batteries listed at 3200mAh when it is the size of the 1600mAh and last as long as the 1600mAh. These are probably from the 'no-reputation' manufacturers.

Nope, tele-convertors work the same on video and still cameras. If your range is 35 to 350, putting a 2x will make it 70 to 700, and on both video cams and still cams. I use Fuji's 1.5x on my S602 to push the 210mm to 315mm, and on my video cam (12x zoom) 480mm to 720mm (wow!).

 

[darrelchia]

oops ......
:embrass:

 

[CanonShooter]

okay.. here's the two images... those who have teleconverters.. does this look like 2.5X???

With Tele:

Without:

Sigh..

Thanks for everyone who tried to help!

 

[wacko]

wah, that's like 1.2X only...

 

[yowch]

yup, looks less than my 1.5x, probably as what wacko said.

 

[sk_online]

Got about that range also with the Vitacon 2x I returned, maybe u can go back and replace with other things of same or higher value with top-up.. like what i did.

 

[stk]

A number of people have reported similar experience with Vitacon teleconverters. You'd probably be safer looking at other brands like Olympus, Canon, Sony, Raynox etc.. Do bring along your camera when shopping for a TC so that u can test the magnification, vignetting etc..

 

[mpenza]

sorry to say but this is totally wrong. focal length is directly proportional to image size.

sorry to say but you are wrong. image size (2 dimensaional) is proportional to the square of focal length (single dimensional).

 

[vince123123]

Instead of trying to measure image sizes and using the eye to gauge, why dont u try my suggestion? (assuming u have a zoom lens, best is one that is capable of at least 2.5x zoom, if not just try the upper and lower ends of ur zoom.)

ie shoot at 40mm + 2.5x convertor
then shoot at 100mm without convertor

compare the two images and see.

that will be more accurate than agar agar images with and without convertors on the same focal length.

in any event, if the box says 2.5x and u can show its not 2.5x, you have the right to get a refund from the retailer.

okay.. here's the two images... those who have teleconverters.. does this look like 2.5X???

With Tele:

Without:

Sigh..

Thanks for everyone who tried to help!

 

[wacko]

sorry to say but you are wrong. image size (2 dimensaional) is proportional to the square of focal length (single dimensional).

you have been mistaken, size is commonly used in the one-dimensional aspect, two-dimensional description would be image area.

 

[mpenza]

you have been mistaken, size is commonly used in the one-dimensional aspect, two-dimensional description would be image area.

errhh.... this is arguable. but good to clear up that the confusion is between image size/area (2 dimension) and your image size (single-dimensional).

 

[Dennis]

The pic sure does not looks like 2.5x. It is worst than a magnifier put in front of the lens. Better get it changed.
BTW I have not seen any manufacturer put in information like that unless the 2.5x is parts of the name of the lens or model. i.e. super 2.5x etc where the 2.5x is simply part of the name but not in anyway indicate that it is a 2.5x magnification tele converter, unless there is some specification or mention that it is a 2.5x tele converter. Many times we are fooled into thinking that the name means what it is next time better to look at some spec if they are available.

 

[yowch]

that will be more accurate than agar agar images with and without convertors on the same focal length.

For vince123123 and those intersted in Malay language, the word is "agak-agak" which means "guessing within some tolerance".

for mpenza and wacko, the multiplier of 2.5x (for example) is to be applied to the focal length, e.g. 100mm + 2.5x filter/lens = 250mm equivalent. In 35mm reckoning, 100mm is 20 (deg) horizontal FOV and 250mm is 8 (deg). Focusing at 40m, 100mm captures 14.4m horizontally, while 250mm captures 5.72m horizontally. The ratio is 14.4/5.72 =2.5. So the 2.5x convertor converts linearly, not by area. This info was calculated on my Palmpilot, using pCAM from www.davideubank.com. This is how I understand the use of the multiplier on convertors.

Given the heat in this discussion, I sure hope that I'm right!

 

[CanonShooter]

Hi yowch,
thanks for your explanation.. so if you say that the lens will extend my focal length.. so is the method suggested by vince123123 also correct?

ie shoot at 40mm + 2.5x convertor
then shoot at 100mm without convertor

I used my slr at 80mm + 2.5X convertor and just 200mm...

The two images were worlds apart.. so I guess the 2.5x lens is not as high a magnification as it claims?

Anyway, I plan to go back to the shop and see what they have to say...