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Extension tubes and 'speed boosters'


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Couple of questions:

Is there a fixed relationship between an extension tube and the lens you're using it with. i.e. If I stick a 10mm extension tube onto a 50mm lens does it alter the total focal length of the lens? If not what does it alter? I know that less light will hit the sensor.

If the lens were a zoom lens would the relationship be linear?

How do 'speed boosters' work. How can sticking an extra element in between a lens and a sensor increase the aperture of that lens? This I do not understand at all blink.png

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Supplementary question. Which is better for a cheapskate macro facility. Extension tubes with all the contacts for AF etc. or a Raynox DC150 or 250?

I'd go with Raynox 150 if on a macro lens, 250 if on a non-macro lens.

These are good. I'm after one for my Pentax D-FA 100/2.8 WR. Also look at Zerene Stacker.

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While the question is being asked, I would also like to add, are close up filters any good for the purpose of getting a shorter minimum focusing distance?

Drawbacks if any?

I have never even heard of speed boosters cheers for bringing the subject up it up and for the links others have posted.

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