Do they change both the focal length and the close focus limit, or just the focal length?
Will it allow me to get closer, or will it just give me a larger image (from a distance where I could already focus)?
/Anders
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Macro Conversion Lenses
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I think they are diopters - meaning they let you get closer thus giving a larger magnification.
Cheers
James
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Are you saying I get greater magnification "only" because I can get closer?
BTW: What defines a diopter? From your answer I guess they are not focal length multipliers.
Actually my original question is valid for wide angle conversion lenses also. They're typically described as changing the focal length by a certain factor. Do they also change the close focus limit?
/Anders
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Hi Anders,
Do a search, I've explained this one before.
Cheers
James
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The effect of the close up filter is that you can get closer to the subject.
First it makes the effective focal lenght shorter. like a negative teleconverter ie, you put one on a 100mm lens it will reduce it to a 80mm lens maby.
The second effect is that it allows you to focus closer. i.e. f the minimum focus distance was 1 ft before, it may now be 6 inches.
When the two effects are combined, the later is more powerfull thus you get slightly more magnification, but not nearly as much as the ammout closer you are would suggest.
The advantage of close up filters is that you do not loose light. Teleconverters or extnsion tubes wich can also be used to enhance macro, steal light and thus effect AF and shutter speed.
The disadvantage to close up filters is that they no longer allow you to focus at infinity.
A close up filter is just a lens mounted backwards on another lens. There is nothing special about the close up filter, you can test this by taking any lens and placing it backwards in front of the camera. The effect is that it will bring infinity focus to a magnification of the ratio of the two lenses. Thus if you place a 50 mm lens in front of a 100mm lens infinity will now be at 2:1 magnification. Most close up filters are longer focal lenghths. One may be 300mm. When you monunt this on a 100mm lens the magnification is 1:3.
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I did do a quick search for "macro converter" before posting, and later for "diopter"... (The latter search gave me more interesting results.)
To me a diopter was (is) only an alternative way of specifying the focal length (the inverse of the focal length expressed in meters).
Very interesting description of magnification with the two (different) lenses mounted mirroring each other!
There is another definition of the term magnification: The ratio of the real life size compared to the size on the film plane.
How are these two definitions related? (I'll do a search on this tomorrow.)
I don't get the part about a close up filtrer being a negative teleconverter. Is that different from a wide angle converter? Wouldn't it make more sense if it actually was a teleconverter?
Thanks for answering - both of you, /Anders
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Hi Anders,
This page by Riccardo Polini has one of the best explanations I have seen about the function of diopters, closeup lenses, extension tubes and teleconverters. It is based on Nikon film cameras, but the optical laws and formulae are the same.
Hope this helps you.
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Very interesting description of magnification with the two (different) lenses mounted mirroring each other!
Acroporas's (William's) description of mounting two lenses mirroring one another is simply a description of a diopter/closeup lens - they are both the same thing. They can be used to acheive magnification. In William's description, the second lens mounted on the front of the other lens is just a very expensive diopter with multiple elements.
There is another definition of the term magnification: The ratio of the real life size compared to the size on the film plane.How are these two definitions related? (I'll do a search on this tomorrow.)
The definition of magnificantion is left over from film photography where a subject that filled a frame at 1:1 or "life size magnification" would measure 24-36 mm - the same size as a 35 mm film frame.
I don't get the part about a close up filtrer being a negative teleconverter. Is that different from a wide angle converter? Wouldn't it make more sense if it actually was a teleconverter?If you read Riccardo's description it might help you understand why a closeup filter/diopter is not a teleconverter.
