Question about macro lenses and magnification

[akdwivedi]

Hi

I have a few questions about the macro lenses and extension tubes.

1) Instead of purchasing the 180mm macro, can I use 200/2.8 lens with an extension tube? Will the setup give me the same magnification as 180mm macro lens?

2) What's the relationship between the size of extension tube and the magnification achieved say with a 100mm/200mm lens?

3) Does the extension tube causes loss of light? Any info to show that the effective aperture of a 2.8 aperture lens with a 25mm/30mm extension tube.

thanks for reading my stupid question. Last question, how does a dedicated macro lens (say 180mm) perform for usually day-to-day photography.

regards
Addy

 

[justarius]

Q1: Your 200/2.8 on extension tubes will never rival the quality of a dedicated 180 macro lens. And unless you have 200mm of extension, you are not going to get 1:1. However, you can combine extension with diopter lenses and even teleconvertors to get down to 1:1, it's just going to be more troublesome and unwieldy in the field.

Q2: Quick and dirty approximation: magnification = total extension/focal length. Thus a 50mm lens on 50mm of extension would give you 1:1. A 200mm lens on 50mm of extension gives you 1:4.

Q3. All extension tubes lead to light loss, as you are physically moving the lens away from the film plane. In some cases, vignetting might result as well. I think that the effective aperture will be affected, but don't quote me on this as I'm not to sure.

A dedicate macro lens should still function well as a normal everyday use lens. My 105 micro doubles as a nice portrait lens. A 60mm micro doubles nicely as well as an everyday carry normal lens.

Hope that helps!

 

[akdwivedi]

thanks just.. that was very informative..