Tele-converters? Safe to use ... or what?
A lot of new photographers ask about the bane of lensmen … ye old tele-converter (or T/C).
Yeah, those little 1.4x, 1.7x, 2x or 3x fittings you sandwich between you camera body and the lens you use, supposedly providing you will instant longer lens.
Do NOT be so quick to buy into that idea. While these cheap additions may seem attractive to the photographer on a budget, the image quality goes to heck, real quick, turning your beautiful 70-200mm f/2.8 zoom shot … into a longer, darker, un-sharp image producer.
Always consider buying a better lens, first, unless there just is no way you can pop for it.
The fact is, placing a tele-converter on a 200-500mm f/5-6.3 lens takes away the lens’ infinity focus. Yeah, no kidding. What that means is if you are shooting anything beyond 27 feet from the end of your lens … it is out of focus (OOF). The actual lens focusing mechanism cannot compensate for the additional gap you have just inserted by adding the tele-converter into the mix. So, while you may want to get that bird sitting way up in yonder tree (one hundred yards away) … with your newly created home-made 400-1000mm f/11-13 monster … it will never look sharp. So what's the point? "Yeah, I got the shot!" I don't think you are going to be all that impressed by the result. I know I certainly wasn't, when I did it.
So, be aware that infinity focus, on many lenses will become unusable, once you add this device to your lens.
Using the TAMRON SP AF 70-200mm f/2.8 Di LD MACRO, here are a series of shots taken at 10-feet ... @ 200mm (no T/C); 280mm (1.4x T/C); & 400mm (2x T/C). I had to manually monkey around for the flash to have enough pop to maintain the base f/8 aperture (TTL really gets confused when using a T/C, also, so the “pop-up” flash is effectively useless, even if you try to jack up the flash exposure setting. )
You need to bear in mind that stopped down to f/8 or tighter, these all are going to look acceptable ... if you try to go with a wider aperture ... then the images degrade (see below):
2x T/C wide-open aperture
So, use them as you like, but be prepared for the drawbacks. There are a few.
Last edited by DonSchap; 11-09-2008 at 10:10 PM.
- BFA, Digital Photography
A Photographer Is Forever
Look, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.