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Old Feb 9, 2007, 2:03 PM   #1
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I have read that extension tubes allow a normal lens to be used as a macro lens because it basically extends the distance between the camera and the lens. So I picked up a Asahi K mount extenstion tube set, with three tubes labeled #1, #2, and #3.#1 is the shortest, and #3 the longest.

I hook everything up, all 3 tubes and my manual 28mm lens. I can not manuallyfocus clearly on anything even if it is only 1mm away from the lens. I take off tube #3. Finally I can start to make out some images. My question is, how do you calculate the maximum number of tubes I can attach to a lens? If I use a lens with a longer focal length such as 50mm, will I be able to focus using all 3 tubes? If I wanted greater magnification, beside a reverse macro ring, what other options are there? I just thought I could add more tubes!!! Haha... now I see how funny that idea is!

Thanks in advance!
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Old Feb 9, 2007, 4:19 PM   #2
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Start at at least 50 mm, with a 28 mm youcan focus very nearalso without extension,but still get a very small magnification (or rather diminishication).The longer the lens, the longer the tube(s). A longer lens allows you to focus from a farther distance. But shooting macro always means focussing close.

You can use any lens with extension tubes, but a dedicated macro always gives better results, with or without extension tubes. I have a Pentax SMC-M 100 mm f4 Macro, and I'm very satisfied with the results (given that I do my part of the job OK). The Vivitar Series 1 105 mm Macro is highly regarded by those who have it.

Kjell

Sample, 100 mm + 3 extension tubes (68 mm in all)


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Old Feb 9, 2007, 5:42 PM   #3
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oh my kjell. looks like i need to get ready for macro season..

roy
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Old Feb 9, 2007, 6:23 PM   #4
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Oh, wow! Kjell - lovely shot.

Kjell - let's see if I got this right - you took it with a macro lens and extension tubes? What does the extension tubes give you that you don't get from a macro lens (I'm confused, as usual). I thought that extension tubes didn't change the lens ability to magnify, just its ability to focus closer and made the DOF smaller. A dedicated macro lens can already focus pretty closely (my cheapie100mm can focus as close as I'm willing to get to my subjects, sometimes closer) so by adding additional extension tubes, you'd be right on top of your subject, wouldn't you? Or do I have this all wrong (like normal).

The little bit I did with my home-made extension tube was with a sharp 50mm lens. I figured anything wider wouldn't help all that much. And the one I was using had such a tiny DOF, even when I was shooting with the lens completely stopped down.
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Old Feb 10, 2007, 5:17 AM   #5
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mtngal wrote:
Quote:
Oh, wow! Kjell - lovely shot.

Kjell - let's see if I got this right - you took it with a macro lens and extension tubes? What does the extension tubes give you that you don't get from a macro lens (I'm confused, as usual). I thought that extension tubes didn't change the lens ability to magnify, just its ability to focus closer and made the DOF smaller. A dedicated macro lens can already focus pretty closely (my cheapie100mm can focus as close as I'm willing to get to my subjects, sometimes closer) so by adding additional extension tubes, you'd be right on top of your subject, wouldn't you? Or do I have this all wrong (like normal).
Even macro lenses differ from each other. The Vivitar gives, as I understand it, a magnification of 1:1. My Pentax 100 mm "only" allows 1:2. I guess the difference is that the Vivitar is built to allow you to get closer to the subjectthan with the Pentax, when using shortest possible focussing distance. The closest I get with my lens is 45 cm (1.48 feet). But with extension tubes attached, I can get closer also with the Pentax, thus getting that 1:1 ratio, or even more.Of course, with the extension tubes attached, I can't focus the Pentax to infinity. Somehow that has never been a problem when shooting macro.:-)

As I understand it, the main difference between dedicated macro lenses and other lenses is not the magnification factor per se, but that the macro lenses give you a flat field with less distortion at the edges. That can be of importance when taking photos of things like stamps. Any lens can magnify with extension tubes.

Roy and Hogrider, help us out here. Does the extension tube really give less DOF at the same aperture, or is it just because you focus closer that it appears like that?

Kjell
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