Extreme macro

Started 2 months ago | Questions thread
petrochemist Senior Member • Posts: 2,651
Re: Definitions

jimhughes wrote:

Leonard Migliore wrote:

jimhughes wrote:

D Cox wrote:

jimhughes wrote:

Filters and extension tubes don't increase "magnification" - they just reduce the minimum focus distance. 2 macro lenses of the same focal length might have different minimum focus distances, so the subject will fill different amounts of the frame.

They certainly do increase magnification. Using either a close-up lens, an extension tube or a bellows will give a bigger image of the object on the sensor. You will probably need to re-focus.

The image on the sensor doesn't get bigger unless you move closer.

Well, if you put an extension tube or a close-up lens on a camera lens, you have to move closer to be in focus. That's the whole point of those devices. Note that if you move closer to an object than the lens's minimum focus distance, the magnification will increase. It just won't be in focus.

Magnification has a specific definition in optics. It's the ratio of the image size to the object size. Period. Please do not redefine it.

I agree to the extent that another term for "reproduction ratio" is "photographic magnification".

Adding a so-called closeup filter does not in itself increase this, as one can see by experiment. It does allow you to increase it by further reducing the distance to the subject and re-focusing.

Here's how Nikon puts it:

https://imaging.nikon.com/lineup/dslr/basics/19/04.htm

Reproduction ratio is a term used specifically for the final print (usually in books). It is totally meaningless for digital files unless you are describing how they are output. Viewing the same digital file on a s,art phone or a 40" screen will have different reproduction ratios.

Magnification is generally used for an optical system, it is often misused with telescopes to indicate the ratio of an unadided view compared to the one through the telescope, but with the exception of that it refers to subject size compared to image size with the image being either at the eyepiece or on the sensor.

By careful selection of lens, subject distance & tube/diopter it is possible to 'fight the effect' ie to take a photograph at the same distance both with & without the tube/diopter. In which case the image size will be the same with tubes and actually reduced with a diopter.

An example with tubes would be a very long lens, with subject near it's native MFD, then adding a short extension tube & refocusing so as to keep the same subject distance. This will have the same magnification, but if you try it with a more normal lens you'll probably find the camera has to move closer to get the subject focused. The idea of adding extension is to allow you to focus closer, not just to replace some of the lenses normal focusing movement.

Likewise with a (weak) +1 diopter supplementary fitted a normal lens will focus to a maximum of 1m, which is a distance many lenses can focus down to without the diopter. If you do this the image with the diopter will be smaller, as the diopter actually reduces the focal length of the combined optical system when it is added. Again the idea of the diopter is to allow the camera to focus closer IF you do that you will get a larger image by using the diopter. You can fight the affect with a weak diopter, but there aren't many lenses that you can add a +10 diopter to & still have an overlapping focusing range - that would require a lens that can focus all the way from infinity down to 10cm.

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