To Teleconvert or Not to Teleconvert

slickhare

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So I'm looking into a new lens in the near future hopefully; an 18-180mm probably. I was considering adding a teleconverter to the mix to make the lens even more worthwhile. But I'm not exactly sure how they work. I know you snap it on behind the lens to increase the focal length, but does that magnify everything you shoot, or just extend your maximum focal length?

also are there any drawbacks to using a teleconverter?
 

fmw

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They magnify the view of the lens in front of them. The drawback is reduced image quality, particularly with zoom lenses.
 

Alex_B

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I can only agree with Fred here.

I only use a TC with prime lenses, and I only use a TC with a rather small magnification factor (I use a 1.4x TC), since I was not happy with results with 2x TCs and with zoom lenses.

Also you should have a lens with a rather wide maximum aperture, at least f/4, but better f/2.8 since the TC will effecively reduce the amount of light that hits your sensor or film.
 

Don Simon

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I wouldn't do it.

General rule for lenses: the longer the zoom range, the poorer the image quality at any given length.

Sticking more glass behing the lens reduces the image quality.

General rule for teleconverters: the higher the magnification, the poorer the image quality.

So as already pointed out, you might want to use a teleconverter on a good prime lens. You could probably get away with using a teleconverter on a 3x zoom, but preferably only a 1.4x tc. A 2x teleconverter on a 10x zoom? Eww...

Oh and image quality aside, as Alex says a teleconveter will reduce the amount of light reaching the sensor... with a 2x teleconverter your 18-180mm f/3.5-5.6 would become nearly f/8 at the short end, and f/11 at the long end... that is slow, and you'd almost certainly lose autofocus.
 

mysteryscribe

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Now for page two.... the rest of the story

I have them in two different sizes. If you dont have a five hundred millimeter lens but one day you see a train wreck and the shot you want you can only get with the second bit of glass added, I want the option to stick it on and accept the softening.

It's just a matter of economics with me. If I can't afford a thousand mm lens to use once in a blue moon but I have a 300mm lens thats is more useful to me. When I need to have a thousand mm that one time a year, I'm going to stick on the 300mm with 3x converter and live with the softness. Better a soft shot than no shot at all is my thinking.
 

Don Simon

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Absolutely, if you need the shot then it's better to have a soft image than none... but I think you can reach a point where the quality is degraded so much that there may be no significant benefit over cropping and enlarging/interpolating.
 

mysteryscribe

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That is an interesting thought. Wonder what the difference really is. I suppose I have my new project.....I have all the glass and can do all the crop and editing digitally. Now it really is a worth project for next week.

Why do i feel like myth busters on tv... My defense is that when i started trying to make a living at photography, it quickly became obvious that I could not charge as much for darkroom work as I could for shooting. But I could add the cost of a prolab's work into my bill here and there. So I didn't do a lot of cropping, the teleextender fullfilled a need I had at the time and I got used to using it. However I will give this a test this week and let you know.
 
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slickhare

slickhare

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So what exactly to macro extension tubes do? "reduce" your focal length?
 

Garbz

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I have used 2 teleconverters in the past. One was a 2x with some zooming L series. (80-200?) attached to a Canon 20D, and the other is a 2x attached to a god-aweful vivitar 70-150mm lens.

Now the photos from the L series lens were wonderful and sharp even with the teleconverter. Yes you are using only half the glass, but you are using by far the best portion, the portion not suffering as badly from chromatic aberration or softness from aspherical elements. The photos from the Vivitar were awful. But the key here was it is an awful lens to begin with. The photos still came out better than they do cropped / resized.

So to quote a bad movie. "I'd rather have it and not need it than need it and not have it."
 

fmw

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So what exactly to macro extension tubes do? "reduce" your focal length?

They separate the lens from the camera body. That moves their focusing range closer. They allow the lens to focus more closely but no longer focus at a distance.
 

fmw

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I have a teleconverter but seldom use it. It is a 1.4X. Image quality with fixed focal length telephotos is just fine. With zooms it is dicey. I've tested very high quality 2X converters and never been happy with the results personally. I owned two of them and dumped them both on Ebay. One was the respected Nikon TC200.

I'm of the opinion that you simply can't get every great image that crosses your eyes. You get what you can and make the most of it. If I miss an image because I don't have a 1000mm telephoto then I miss it. I shrug. You can't have everything.

Garbz's comment is quite valid. If you are using a lens made for 35mm on an APS digital sensor, you use just the central sweet spot of the lens field of view. That tends to cure a lot of evils.
 

Alex_B

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Garbz's comment is quite valid. If you are using a lens made for 35mm on an APS digital sensor, you use just the central sweet spot of the lens. That tends to cure a lot of evils.


But with respect to final print size, the resolution of that lens in the sweet spot is reduced according to the crop factor. I have to admit that is a minor effect since you often have a very good resolution there to start with.

It also depends on how extended your sweet "spot" really is, this might vary and you will not get constant image quality over the whole APS-area with most lenses made for 35mm.
 

mysteryscribe

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Okay, test one is complete and a total failure.

Test two later but the problem wasn't really with the adapters, it was with me. I had forgotten how much the extenders would change the exposure. The extenders had camera movement. Next time I'm going to have to set up my tripod and cable release. Also start with a better lens I think.
 

Garbz

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True Alex I should have made it clearer, you DO suffer quality problems. The key though is that these problems are not as bad as they look if you crop the image and the resize it back to "fake" a teleconverter.
 

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