Teleconverter question


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philip827

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Hi ppl... have a question here...
my camera has 28-200mm lens, 7x zoom.If i fit a 2.5x tele on it, what will i get? 9.5x?
And what is the purpose of the teleconverter? To have more magnification to take bird photos and macro?
Thanks for helping me out here...
 

justarius

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philip827 said:
Hi ppl... have a question here...
my camera has 28-200mm lens, 7x zoom.If i fit a 2.5x tele on it, what will i get? 9.5x?
And what is the purpose of the teleconverter? To have more magnification to take bird photos and macro?
Thanks for helping me out here...
A bit of a nitpick: A description of a lens as a 7X zoom is quite useless to other people. 10-70 is 7x. So is your 28-200. And yet, they are very different things. A something X zoom is just a useless marketing term thought up by the companies to razzle dazzle the public. ;)

A teleconvertor basically magnifies the image produce by the lens to give you greater reach. Do note that since you are magnifiying the image, all flaws of the lens are magnified as well, and new flaws maybe introduced by the TC.

A TC multiplies against the focal length. So your 28-200 under a 2.5X TC becomes an effective 70-500 lens (note its still a 7x zoom if you want to think about it).

People uses TC to get more reach. It's not uncommon for wildlife, especially bird photographers, to have a 1.5X or 2X TC permanently attached to their (already very long) lens. TC's are also of use in macro photography, as adding a 2X TC to a 1:1 macro lens means that you get a 2:1 reproduction ratio as you retain the minimum focussing distance when you use a TC.
 

philip827

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justarius said:
A TC multiplies against the focal length. So your 28-200 under a 2.5X TC becomes an effective 70-500 lens (note its still a 7x zoom if you want to think about it).

People uses TC to get more reach. It's not uncommon for wildlife, especially bird photographers, to have a 1.5X or 2X TC permanently attached to their (already very long) lens. TC's are also of use in macro photography, as adding a 2X TC to a 1:1 macro lens means that you get a 2:1 reproduction ratio as you retain the minimum focussing distance when you use a TC.
so with the TC on... i have a 500mm effective lens? sry ar all these terms quite chim to me still...
 

justarius

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hwchoy said:
so justarius, how is a TC different from a close-up filter? both are magnifying glasses yes?
A closeup filter (quoting John Shaw), works by reducing the effective focal length of the lens on which they are used.

Effective focal length = 1000 / [(1000/focal length of lens) + diopter power]

All closeup filter make whatever lens they are added to focus at the same working distance if the lenses are set to the same focussing distance. So, with a 50mm, a 100mm, and a 300mm all set at infinity focus, a +3 diopter added to each will make them focus at the exact same working distance.

Thus if all lenses will be in focus at the same working distancce, it follows that the longer the focal length, the greater the magnification you get.

Magnification = FL of camera lens / FL of diopter, where FL of diopter = 1000/diopter power.


Teleconvertors on the other hand are optical magnifiers. They multiply the magnification of your subjec twhile allowing you to get a bigger image from th same working distance.


Thus a closeup lens works by reducing your working distance, allowing you to focus closer to get the needed magnification.

A teleconvertor maintains the working distance of your original lens, but magnifies the image.


(above thanks to 'John Shaw's Nature Photography Field Guide', a most excellent book!)
 

justarius

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hwchoy said:
wow thanx for the explanation. I just confused over the formulation. for lens FL do I use the 35mm equivalent?
Yes. Don't get too hung up over the formulas though, as they are just a rough gauge. Nothing beats actually mounting the thing on and seeing the effect.

Problem for maths buffs:

What's the magnification of the following setup

Nikon 4T closeup lens + AF 105mm Micro-Nikkor at 1:1 + Nikon PN-11 (52.5mm extension tube) + Kenko Pro 2X TC?

I don't know the magnification, but it's big enough to see the individual colour dots on a menu!
 

hwchoy

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I have tried attaching +9 close-up (Canon 250D, Hoya +4, Hoya +1) and Canon TC58N (1.75×), actually found the magnification got reduced with the TC.
 

justarius

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hwchoy said:
I have tried attaching +9 close-up (Canon 250D, Hoya +4, Hoya +1) and Canon TC58N (1.75×), actually found the magnification got reduced with the TC.
I think we are getting way OT, but...

I don't know if digicam's TC works the same way as SLR TC's, as the digicam TC screw infront like a filter, while SLR TCs go behind the lens. So I don't know if your working distance is changed with a digicam TC, but you can test it out...
 

foxtwo

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justarius said:
Nikon 4T closeup lens + AF 105mm Micro-Nikkor at 1:1 + Nikon PN-11 (52.5mm extension tube) + Kenko Pro 2X TC?

I don't know the magnification, but it's big enough to see the individual colour dots on a menu!
wats the approximate price of a nikon 4T?
 

quekky

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finnally understand how closeup filter and TC works. so how does ext tube works?


maybe that day we should have shot a ruler instead
 

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