# How should I use close up filters?

I asked one question about macro adapters and one tells me about close up filters and I don't get it. He tells "+1 = 1000mm, +2 = 500mm, +3 = 333mm,..." and when he tells me about how to use them, I can't figure it out.

This lash-up now allows you to focus on an object 250mm (10 inches) from the front of the lens

I totally get it. It says that 'now an object that is 10 inches away from the lens, can be focused', right?

But what does he say by this?

Generally, the normal focus range is about equal to1 additional diopter power. Thus the natural focusing range of the camera allows you to achieve focus down to about 200mm (8 inches).

• He says normal MFD of a lens is 1 meter, right? (does 'a normal lens has a +1 diopter' mean the same?)

• You camera has a natural range of focus distance. Unusually, infinity to about 1 meter (3 feet). Mount a supplemental lens +3 and with the camera set to infinity your focus distance is now 333mm

So, a +5 close up filter reduces the infinity normal MFD to 200mm? And now an object that is 8 inches away from the lens, can be focused? The millimeter equivalent thing of the close up filter gives the lens the ability to have a MFD of the equivalent millimeters, am I correct?
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• +2 → 500mm
• +3 → 333mm
• +4 → 250mm

And again, I completely don't get what he has said on the 4th comment..

The numbers, +1, +2, +3, etc., are diopters—units of refractive power equal to the reciprocal of the focal length in metres for any given lens.

In simple terms:

When placed in front of a lens, the effective focal length is divided by the amount of diopter power.

Practically speaking…

Parallel rays of light (from an object at infinity, say) focus through a
+1 lens at one metre (1000 mm) from the lens
+2 lens at one-half a metre (500 mm) from the lens
+3 lens at one-third a metre (333 mm) from the lens
… etc.

The take-away here is that your results will be similar to this by these ratios. You probably won't be exactly a metre away from the object; but, if you're a couple of metres away you can expect proportionally similar image magnification.

Important NOTE: The use of a meniscus lens/supplementary lens/close-up filter is not an optimal optical solution and there will be chromatic aberration and linear distortion in your images; but, they will appear predictably bigger. Use of extension tubes will give an improved image over that of supplementary lens although less compact and requiring increased exposure times.

• @ Stan – Diverging rays of light from a nearby object will be rendered parallel. +1 lens -- object at 1 meter distant is performs as if it were at infinity. +2 lens -- object at 500mm distant is performs as if it were at infinity. +3 lens -- object at 333mm distant is performs as if it were at infinity. +4 lens object at 250mm distant is performs as if it were at infinity. An achromatic supplemental lens preforms surprising well, Jan 14, 2017 at 16:59
• @AlanMarcus Sure. With all due respect, that thin lens stuff should be edited into your answer, not mine. It's irrelevant in this context. I don't see how your comment clarifies my explanation to the original post. If anything, such parenthetical detail although true appears counterintuitive and confusing when simple explanation was requested.
– Stan
Jan 16, 2017 at 7:29

You want to take a close up picture. Your camera will not focus close enough. You mount a supplemental close up lens (also called a close up filter). This lens fits before your standard camera lens. The camera now equipped with a close up lens will focus on objects far closer than without. One could call this lens a micro adapter but that is not jargon I am accustomed to.

If you mount a +1 and the camera is set to infinity (as far as the eye can see), an object is in focus that is 1000mm from the camera lens. You can move the camera in closer. Likely the closest you can get and achieve focus is 500mm. Note many cameras will allow you to get even closer.

Mount a +2 and you can focus on an object that is 500mm away, and likely you can continue to move closer to 333mm.

Mount a +3 and achieve focus at 333mm. Likely you can continue moving closer till you are 250mm away.

Mount a +4 and achieve focus at 250mm from the front lens. Likely you can continue moving closer to 200mm.

In other words, a supplemental close up will allow you to move closer. The stronger supplemental lens, the closer you can work.

Additionally each lens, depending on power, will afford you a range of distance that achieves focus.

Go to the drug store and buy cheap +3 reading eyeglasses and hold or tape one of the lenses over you existing camera lens. Thus you teach yourself how this works.

• Diverging rays of light from a nearby object will be rendered parallel. +1 lens -- object at 1 meter distant is performs as if it were at infinity. +2 lens -- object at 500mm distant is performs as if it were at infinity. +3 lens -- object at 333mm distant is performs as if it were at infinity. +4 lens object at 250mm distant is performs as if it were at infinity. An achromatic supplemental lens preforms surprising well, – Alan Marcus
– Stan
Jan 16, 2017 at 7:21