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Macro lenses with extension tubes

Started Feb 16, 2019 | Questions thread
bclaff Forum Pro • Posts: 13,920
Re: Macro lenses with extension tubes

EofC wrote:

Hi all

Is there a way to accurately calculate new closest focusing distances and magnification ratios of 1:1 macro lenses when used with extension tubes?

Do results differ between internal and external focusing lenses?

The online tools I've found don't give consistent results and seem to be designed with standard lenses in mind.

Thanks for any insights...

As has been said, the focal length when focused closer than infinity is often lower and therefore the effect of the extension tube is more magnification.

It's not hard to measure focal length if you have extension tubes.
Here's an example .

This calculator will give good results. The more you know about the lens, the more accurate it will be.

Of course if you measure focal length using the above technique you will already have your answer for things like working distance

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Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

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