Wednesday, February 20, 2008

Extension Tubes verses Close-up Filters

A frequent question that seems to pop up a lot is “What’s better; extension tubes or close-up filters?” and the answer isn’t as simple as some of you might think…

The general theory is that an extension tube is going to give you a sharper image because it’s an air gap and, unlike a close-up filter, there is no additional glass. An extension tube magnifies an image by increasing the size of the image circle that a lens projects onto the sensor, so the only negative aspect is a decrease in light reaching the sensor and a dimmer image in the view finder. On the surface that seems like a logical answer, but it’s just not that simple…

Non-macro lenses are designed to be sharp when focused toward infinity, and not when focused at the minimum focusing distance of the lens. Adding an extension tube to a non-macro lens just makes the problem worse since any image softness at the minimum focusing distance is just getting magnified.

But a close-up filter, like the 500D, changes the way that a non-macro lens focuses and it will actually cause a lens to be just as sharp at minimum focus as it normally is at infinity –something that an extension tube won’t do. The effect is so profound that you can see the difference in image quality without having to view a photo at 100% pixels. So the answer to the “What’s better?” question really depends on what lens you’re using…

If you’re shooting with a macro lens then you could argue that the extension tube is better, since a macro lens is designed to be sharp at minimum focus and the tube is just air. But as long as it’s a high quality, dual element, close-up lens like the 500D the image quality is just as good as using a tube.

There is one other advantage to using a close-up filter over an extension tube: The filter magnifies the light before it enters the lens, so there is no light loss and having a brighter image in the view finder makes focusing the scene a lot easier…

5 comments:

Orion said...

Thanks for sharing :). I use Raynox DCR250 on top of my Tamron SP90 which gives me approximately 1.68x. I like this better than the extension tube because i can snap my dcr250 on easily.

Dalantech said...

When I was shooting with the 100mm macro I had a 500D on it all the time :)

Duluoz said...

I purchased the Opteka Close-up lens set to fit on my Canon 28-135mm. One thing I noticed right away is that the camera began over exposing the shots. I have to apply a healthy dose of exposure compensation whenever I use them. Is this because the close-up lens is cheaply made or is it the nature of the lenses to do that.

Dalantech said...

@ duluoz: I've never had exposure problems with the Canon 500D close-up lens and I've used it on three different camera bodies and two lenses.

Marek said...

Sometimes I'm trying to use 250D with my EF100/2.8 maco (C 40D) but having this installed picture in viewfinder is lets say cloudy (foggy). AF of course has a problems specially close to 1:1 setting on lens so more often manual focusing is working. Final RAW is fog free and is sharp more or less as without 250D.