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ducklite
10-02-2007, 07:50 PM
Anyone use a teleconverter? I've got a situation coming up where I need the power of a 400mm zoom, and only have an 80-200. I'm concerned about degradation. It would be Nikkor. Thoughts?

boBQuincy
10-02-2007, 08:49 PM
A good teleconverter on a good lens does not show much degradation. I use a Canon 1.4x on their 70-200 f/4 and really can't see much difference in sharpness and contrast. Nikon's version is probably just as good.
I would expect the 2x to lose a bit more but still be very good.

A long time ago I used an inexpensive teleconverter on an inexpensive lens and would have been better off just enlarging the image that much more instead.

MarkBarbieri
10-02-2007, 09:08 PM
I use the Canon 1.4x and 2.0x converters on a Canon 70-200 f/2.8 lens. Then 1.4x doesn't show noticeable degredation, but the 2.0x definitely does. I've been told that the same is true of the Nikon equivalents, but I haven't seen the comparisons. I usually use the 1.4x and crop rather than use the 2.0x. Only when I think I'm going to do considerable cropping even with the 2.0x do I use it.

As a quick trivia question, anyone know why every 1.4x teleconverter from every manufacturer results in a 1 stop loss of light and every 2.0x teleconverter results in a 2 stop loss of light?

Code
10-02-2007, 10:30 PM
As a quick trivia question, anyone know why every 1.4x teleconverter from every manufacturer results in a 1 stop loss of light and every 2.0x teleconverter results in a 2 stop loss of light?

I know why, I just really stink at teaching things like this ;)

First of all, when you move up 1 stop, you are reducing the amount of light reaching the sensor/film by half. f5.6 is half as much light as f4, one quarter as much as f2.8, etc.

A teleconverter "zooms in" on the image coming from the lens, but it obviously can't add any light. You have to think of the area of the image that is being used, and area increases as the square of width and length (doubling the length of the sides of a square quadruples the area of the square). So a 2x teleconverter is "stretching" one quarter of the image to fill the whole frame, meaning one quarter as much light for the sensor, that's a 2 stop difference. A 1.4x teleconverter "stretches" half the image (the square root of 2 is 1.4142..), meaning half as much light, that's a 1 stop difference. That also explains why it's a 1.4x teleconverter and not a 1.5x (I've heard that question a few times).

Hmm, how did I do?

0bli0
10-02-2007, 10:51 PM
personally, i prefer to use two 1.4x over a single 2x from a sharpness perspective.

the biggest problem is light loss and also how it affects AF. a 2.0 causes 2 stops of light loss. remember that aperture is a ratio of opening to focal length. if you effectively double the focal length, the lens opening diameter needs to be four times the size to keep the same aperture ratio - however with a teleconverter, it remains exactly the same.

this loss of light in turn lowers the effectiveness of the autofocus due to the increased difficulty in detecting contrast. if the OP is using the 80-200 2.8, it will at least still work. if the lens were slower, chances are it wouldn't - at least not for sports.

edit - don't you hate it when you are composing a response and then are distracted - only to return and have posted what someone else already said...
btw - that's why full aperture stops go 1, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16

Gdad
10-03-2007, 05:09 AM
I have used a 1.7x on my 70-200/2.8vr Nikon Lens. It makes it a 340mm f4.8 IIRC- Sharpness was fine but it did slow down the AF a bit.

ducklite
10-03-2007, 01:26 PM
I have used a 1.7x on my 70-200/2.8vr Nikon Lens. It makes it a 340mm f4.8 IIRC- Sharpness was fine but it did slow down the AF a bit.

Perfect--that's exactly the info I was looking for!

Thanks to you and everyone else. :)

Gdad
10-03-2007, 02:45 PM
Perfect--that's exactly the info I was looking for!

Thanks to you and everyone else. :)

I should have said it makes it makes it a 119-340mm f4.8 :thumbsup2

jann1033
10-03-2007, 07:44 PM
follow up question...i was under the impression you should only use them over 100mm or risk damaging the lens or camera( been a while since i read that so as usually my brain is full of cotton) yes or no? wondering as would i have to remove one on my 70-200 if i went below 100? thinking "no" due to gdad's experience?

boBQuincy
10-03-2007, 08:03 PM
follow up question...i was under the impression you should only use them over 100mm or risk damaging the lens or camera( been a while since i read that so as usually my brain is full of cotton) yes or no? wondering as would i have to remove one on my 70-200 if i went below 100? thinking "no" due to gdad's experience?

Nope, as I recall you have Canon's 70-200 f/4 L which is made to work with their L series teleconverters. I have the 1.4x and it works with the 70-200 just great, even with my brain full of cotton! ;)

MarkBarbieri
10-03-2007, 09:20 PM
The Canon teleconverters have an element that protrudes towards the front. Only certain lenses are designed with a recessed area into which this protrusion can fit.

On page 71 of Canon's EF Lens Works III (http://www.canon-europe.com/Support/Documents/digital_slr_educational_tools/en/ef_lens_work_iii_en.asp) (see the section on Single Focal-Length Lenses (http://software.canon-europe.com/files/documents/EF_Lens_Work_Book_3_EN.pdf)), they list the compatible lenses as L-series lenses 135mm and up, as well as the EF 100-400mm f/4.5-5.6L IS USM, the EF 70-200mm f/2.8L IS USM, the EF 70-200mm f/2.8L USM,the EF 70-200mm f/4L IS USM, and the EF 70-200mm f/4L USM.

That does not include non-L telephoto lenses like the 135mm soft-focus lens.

0bli0
10-03-2007, 09:48 PM
i use the tamron pro SP (the white ones which have more elements than the standard black tamron ones). they fit any lens as the don't have the protruding area.

jann1033
10-04-2007, 10:03 AM
i think the kenko pro fits more as well and can be used with f 4 lenses ( at least i know the canon version does, i have enough problem keeping up with 1 line but assuming nikon fit would be similar;) )

Nikel
10-04-2007, 10:13 AM
Just another option for the OP - If you only need this for a specific situation, why not rent a 400mm lens? Unless you think you would use the teleconvertor frequently enough to warrant buying one. I've personally used several different online rental companies (I try before I buy and have no purchasing regrets ;) ). I can list some links for you, if you're interested.

jann1033
10-05-2007, 04:17 PM
i use the tamron pro SP (the white ones which have more elements than the standard black tamron ones). they fit any lens as the don't have the protruding area.

have you ever used this on a f4 lens? according to one report i read it won't autofocus on anything smaller than 2.8..but everything else i read just said it's basically just the same on f4 as the cheaper model...someday i might get an f2.8 (who knows) and it's about 20 less than the kenko( and someone said they are identical just name changed but who knows that either for sure:confused: ) but i don't want to manual focus all the time:rotfl: or is that one of those "put tape over the 3 pin deals"...

thanks

0bli0
10-05-2007, 09:51 PM
jan - yes it will auto-focus on a lens that has a maximum aperture of f/4, or f/5.6 using the centre spot on a 1 series body. but it's going to hunt if there isn't something very contrasty to lock onto.

the tamron sp and the kenko pro are identical. they actually don't have the pins you normally tape over, so you it won't err99 when you try to use it at f/8, but AF just won't ever find anything.

jann1033
10-06-2007, 08:36 AM
thanks oblio

ducklite
10-07-2007, 10:46 AM
Just another option for the OP - If you only need this for a specific situation, why not rent a 400mm lens? Unless you think you would use the teleconvertor frequently enough to warrant buying one. I've personally used several different online rental companies (I try before I buy and have no purchasing regrets ;) ). I can list some links for you, if you're interested.

I would be using it three or four times a year (maybe a little more), so while I can't justify buying a 400mm lens, I can justify spending the $350 or so on the teleconvertor. I think over a couple of years time, it would pay for itself. Plus I would have it any time I needed it, and not have to plan ahead. I am only intrested in the Nikkor.

jann1033
10-10-2007, 01:44 PM
just got the tamron sp and pleased as can be...prelim shots i can't tell any difference between that and the straight 70-200 as far as sharpness, just lots closer:goodvibes ...it's raining so i need to set up my tripod since my hands are like jello today but so far it looks really good...and for the macro even with my less than stellar phoenix with out the 1:1 filter( so 1:2) and tripodless it makes it i would say close to if not more magnified than the 1:1..have to get more scientific on that one too but i'm glad i saved the $100...so far..;) still probably will want the canon macro down the road but at least it buys me some time

i do have 2 questions though.. says the f number="total f number of prime and the converter"so i am guessing that means if it says 5.6 in the viewfinder,it really is 5.6, it isn't really 6.3( deducting the stop of light i lose). and since it's really making my lens more magnified i assume i need a faster shutter to be sure not to show shakes? (ie at 200mm, 1/500 ish with the crop and teleconverter taken into account)