Am I cheated?

CanonShooter · 1st October 2003

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 · 1st October 2003

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 · 1st October 2003

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 · 1st October 2003

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 · 1st October 2003

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 · 1st October 2003

Originally Posted by 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.

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

yowch · 2nd October 2003

Originally Posted by 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.

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 · 2nd October 2003

oops ......

CanonShooter · 2nd October 2003

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 · 2nd October 2003

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

yowch · 2nd October 2003

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

sk_online · 2nd October 2003

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 · 2nd October 2003

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 · 2nd October 2003

Originally Posted by wacko

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 · 2nd October 2003

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.

Originally Posted by 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 · 2nd October 2003

Originally Posted by mpenza

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 · 2nd October 2003

Originally Posted by wacko

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 · 2nd October 2003

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 · 2nd October 2003

Originally Posted by vince123123

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 · 3rd October 2003

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...

1st October 2003	#1
CanonShooter New Member Join Date: Sep 2003 Location: AMK Posts: 20	Am I cheated? 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

1st October 2003	#2
darrelchia Member Join Date: Jul 2003 Posts: 419	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. __________________ my website :: my blog

2nd October 2003	#8
darrelchia Member Join Date: Jul 2003 Posts: 419	oops ...... __________________ my website :: my blog

1st October 2003	#3
mpenza Moderator Join Date: Jan 2002 Location: New York City Posts: 13,397	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.

1st October 2003	#4
vince123123 Deregistered Join Date: Oct 2002 Location: West Posts: 6,689	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

1st October 2003	#5
ST1100 Senior Member Join Date: Jun 2003 Location: Singapore, Bedok Posts: 1,801	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.

2nd October 2003	#10
wacko Member Join Date: Mar 2002 Posts: 440	wah, that's like 1.2X only...

2nd October 2003	#11
yowch Member Join Date: Oct 2002 Location: Singapore, Redhill Posts: 1,063	yup, looks less than my 1.5x, probably as what wacko said.

2nd October 2003	#12
sk_online Member Join Date: Jul 2003 Posts: 270	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.

2nd October 2003	#13
stk Member Join Date: Jan 2002 Location: AMK, Singapore Posts: 610	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..

2nd October 2003	#18
Dennis Senior Member Join Date: Jan 2002 Location: Singapore Posts: 3,862	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.

3rd October 2003	#20
CanonShooter New Member Join Date: Sep 2003 Location: AMK Posts: 20	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...