Teleconverter Queries and Quirks

[fWord]

There's been a couple of questions about teleconverters that's been bugging me for a while. I'm interested in these because I'm looking to extend the range of my 70-200mm f/4 lens without breaking the bank. Recently, I went to the zoo and couldn't get close enough for some shots with the bare lens alone. If I won some money at 4D, I'd probably buy over a 2nd hand 100-400mm f/4.5-5.6 IS, but that's a little far-fetched now.

I'm currently using it with an EOS 350D, which has a 1.6X crop factor.

Please be warned...n00b questions coming up!

How much of an increment will a 1.4X TC give? Which is the accurate calculation?

1. (70 X 1.4) X 1.6 - (200 X 1.4) X 1.6 = 156.8-448mm

2. (70 X 2) - (200 X 2) = 140-400mm

Will the camera still autofocus with the central AF point if I use a 2X TC with this lens?

I've seen the Sigma TCs go for affordable prices. Should I look at this or go for other brands? Probably won't be able to afford a Canon though.

Thank you...looking forward to your replies.

[vince123123]

Lets first discuss the lens and the teleconvertor (and leave the crop factor later).

A 1.4xTC will multiply your focal length by 1.4

Meaning, your 70-200 becomes 70 x 1.4 to 200 x 1.4 = 98 - 280mm lens

The crop factor in your camera doesn't "increase" the focal length of your lens, rather it crops the view by a corresponding amount just as if you had used a 1.6x TC on your lens.

ie.

98 - 280 x 1.6 = 156.8 - 448mm lens.

However, please take note that it isn't really a 156-448 mm lens, ie the bokeh/perspective/etc will still be a 98-280.

Hope this helps.

Originally Posted by fWord There's been a couple of questions about teleconverters that's been bugging me for a while. I'm interested in these because I'm looking to extend the range of my 70-200mm f/4 lens without breaking the bank. Recently, I went to the zoo and couldn't get close enough for some shots with the bare lens alone. If I won some money at 4D, I'd probably buy over a 2nd hand 100-400mm f/4.5-5.6 IS, but that's a little far-fetched now. I'm currently using it with an EOS 350D, which has a 1.6X crop factor. Please be warned...n00b questions coming up! How much of an increment will a 1.4X TC give? Which is the accurate calculation? 1. (70 X 1.4) X 1.6 - (200 X 1.4) X 1.6 = 156.8-448mm 2. (70 X 2) - (200 X 2) = 140-400mm Will the camera still autofocus with the central AF point if I use a 2X TC with this lens? I've seen the Sigma TCs go for affordable prices. Should I look at this or go for other brands? Probably won't be able to afford a Canon though. Thank you...looking forward to your replies.

[dEthANGeL]

With a F4 lens, don't be greedy and stack on a 2x as 2x degrades the image quality quite a far bit. You might also lose some of your focus accuracy as well.

A 1.4x for your lens would be just nice, pushing the fstop to 5.6 which is still tolerable.

2x TCs are more for primes. But also, most try to avoid using it as the PQ would be terrible. Nothing but the actual lens is still

[fWord]

Originally Posted by vince123123 Lets first discuss the lens and the teleconvertor (and leave the crop factor later). A 1.4xTC will multiply your focal length by 1.4 Meaning, your 70-200 becomes 70 x 1.4 to 200 x 1.4 = 98 - 280mm lens The crop factor in your camera doesn't "increase" the focal length of your lens, rather it crops the view by a corresponding amount just as if you had used a 1.6x TC on your lens. ie. 98 - 280 x 1.6 = 156.8 - 448mm lens. However, please take note that it isn't really a 156-448 mm lens, ie the bokeh/perspective/etc will still be a 98-280. Hope this helps.

Beauty! That's excellent. I understand the part about bokeh and appearence of the compressed perspective, but for me, the degree of reach is really much more important than the other two. At least for now.

Wow...448mm sounds marvelous, although the lens will be astoundingly slow. In the zoo when lighting is sometimes pretty muddy, it will present some problems. I've tried shooting handheld even things behind glass, such as the snakes. But the jitters get obvious at 1/80 second at 200mm!

[fWord]

Originally Posted by dEthANGeL With a F4 lens, don't be greedy and stack on a 2x as 2x degrades the image quality quite a far bit. You might also lose some of your focus accuracy as well. A 1.4x for your lens would be just nice, pushing the fstop to 5.6 which is still tolerable. 2x TCs are more for primes. But also, most try to avoid using it as the PQ would be terrible. Nothing but the actual lens is still

*nods* True also...2X TC will give me really good range, but I doubt if I'd get anything usable unless I shoot purely from a tripod.

Looking at the lens book, I don't see too many other solutions to getting added range without spending too much. The 100-400mm mentioned before is a possibility. Failing which, the 400mm f/5.6 looks attractive, only that I'd need to get a bigger box, bigger bag, and learn some discipline to use a prime.

[fWord]

Hmm...will the 1.4X TC also work on the 18-55mm kit lens?

[Reno]

Originally Posted by fWord Hmm...will the 1.4X TC also work on the 18-55mm kit lens?

you have to bring your cam and lens down to try if it works.

[dEthANGeL]

Now why would you want to do that?

Already the F3.5 you'll bring it to F4.5 .. 5.6 you'll bring it to F6 (correct me if i'm wrong) .. kit lens already without USM, you'll be shooting yourself in the leg with that.

TCs generally best for fixed aperture lenses.

[fWord]

Originally Posted by Reno you have to bring your cam and lens down to try if it works.

Yes, I shall do that. I didn't read any specifics about the Teleplus converter, but the impression that I got from reading about the Canon TC was that it couldn't be used on variable aperture lenses. Perhaps I was only assuming.

[fWord]

Originally Posted by dEthANGeL Now why would you want to do that? Already the F3.5 you'll bring it to F4.5 .. 5.6 you'll bring it to F6 (correct me if i'm wrong) .. kit lens already without USM, you'll be shooting yourself in the leg with that. TCs generally best for fixed aperture lenses.

In the zoo, they have both indoor and outdoor exhibits. What I found during my trip was that the 70-200mm was too short for outdoor shots. Indoors, the focal length is just right, but it's terribly difficult to handhold because of the weight and length.

The TC on my kit lens will give me the reach I need, whilist still keeping weight low. Indoors, I'd be using manual focus anyway since I'm shooting behind glass (eg. snake and fish exhibits), so it doesn't matter if the lens becomes an f/8 at the long end and loses AF. One thing I forgot to keep in mind was that the kit lens itself might be difficult to handhold at an f/8 equivalent for indoor things.

Thanks for mentioning this.