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Photo Forum / Digital Photography / DSLR Cameras / January 2005Meaning of a 2 strength close-up diopter for macro
I asked this in another thread but didn't get an answer. Specifically, I'm wondering what effect this would have on a 400mm zoom lense which is only capable of getting as close as 7.5 ft. I don't understand what they mean when they say "changes the closest focusing distance from infinity to 9.9" My current 200mm zoom will get up to 1.3 ft away so I assume this would end up having me a couple inches away. I don't know what exact impact to expect. paul wrote: > OK I found the item I was looking for. > $140 Canon 500D +2 77mm 2-element close-up diopter > http://www.adorama.com/CA77CU500D.html > More info: > http://www.earthboundlight.com/phototips/closeup-diopters.html > http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0005yN > > The descriptions says "changes the closest focusing distance from > infinity to 9.9" > > What exactly does that mean? Sounds like it will not focus on anything > beyond 9.9 inches away. It is supposed to have a very narrow depth of > field but I guess that's a given. Sounds not much quality difference > from a 'real' macro lense except the incovenience of having to unscrew > it for anything over 10 inches away. >I asked this in another thread but didn't get an answer. Specifically, >I'm wondering what effect this would have on a 400mm zoom lense which is [quoted text clipped - 3 lines] >this would end up having me a couple inches away. I don't know what >exact impact to expect. I just got a Hoya close up filter set, and it has +1, +2, and +4 element, and they can be added up... for anything up to +7. I use them on my Sigma zoom, since it can only focus from about 3 feet. I just did a test using the +2+4 combination, and if I zoom to 300mm on a subject 3 feet away with out the filters, I can then take the same picture from about 7" away zoomed back to 28mm, with the +6 filters. This gives some advantages... I posted the example on alt.binaries.photos.original under "Glasses for my camera". The focus range with the +6 is very small, just a few inches back and forth. You use the zoom to adjust the frame... but the camera MUST be about 7" from the subject. These filters are ONLY for macro work - you must take them off to take any other type picture. But they work very well indeed! ($80 is a good price!) +2 means it has a focal length of 1/2 meter. This is a diopter unit (reciprocal focal length) as used in eyeglass prescriptions. It is very handy for calculations, as this example will show... You said your 400-mm lens focuses down to 7.5 feet without a close-up lens attached to it. (This is something you have to know from the lens specifications, of course; it has nothing to do with the 400-mm focal length.) 7.5 feet is about 2 meters. We'll call it 2 meters from here on. The reciprocal of 2 meters is 0.5. The reciprocal of infinity is effectively 0. So your lens currently covers a distance range (measured in diopter units) of 0 to 0.5. The close-up attachment will add 2 to this, making its range (in the same units) be 2.0 to 2.5. It will then focus from 1/2 meter down to 1/2.5 meter (i.e., from 20 inches down to 16 inches). That's how close you can get. >+2 means it has a focal length of 1/2 meter. This is a diopter unit >(reciprocal focal length) as used in eyeglass prescriptions. It is very [quoted text clipped - 20 lines] > >That's how close you can get. That's useful info - thanks. Do most lenses have the diopter info for them available? Or do you have to figure it yourself? > That's useful info - thanks. Do most lenses have the diopter info for > them > available? Or do you have to figure it yourself? You have to take the minimum focusing distance (given in the lens specifications) and convert it to diopters by convering it to meters and taking the reciprocal. I need to make a web page about this. This system of measurement is familiar to every eye doctor (which I am not) but photographers rarely encounter it.  SignatureClear skies, Michael A. Covington Author, Astrophotography for the Amateur www.covingtoninnovations.com/astromenu.html >> That's useful info - thanks. Do most lenses have the diopter info for >> them [quoted text clipped - 7 lines] >familiar to every eye doctor (which I am not) but photographers rarely >encounter it. I think I'll make a spread sheet of all my lenses and my +1 - +7 diopter kit for all the distances... right now I'm kind of guessing on which lens to pick out! Now, if I can just figure out the field of view... ! > Now, if I can just figure out the field of view... ! Not too difficult, but more than I can express in a short newsgroup posting. >> Now, if I can just figure out the field of view... ! > >Not too difficult, but more than I can express in a short newsgroup posting. Is there a spec for distance for field of view with macro? I guess I should take pictures of a yardstick in focus and get an idea that way... I really am only concerned with taking product shots in focus for my site. A direct experiment is the quickest way to find out. Field of view is basic trigonometry. Just pretend your lens (of focal length X) is a pinhole X distance from the film, and solve the triangles. Adding a +2 close-up lens (or whatever) keeps your lens the same distance away from the film, but lets you get an in-focus image of a nearer subject. That's the simplest way to approach the calculations. I've placed on my "to-do list" the making of a web page that explains all this in more detail... >>> Now, if I can just figure out the field of view... ! >> [quoted text clipped - 6 lines] > > I really am only concerned with taking product shots in focus for my site. So an out of focus shot at the distance calculated is going to be what you get, that's simple. > A direct experiment is the quickest way to find out. > [quoted text clipped - 18 lines] >> >>I really am only concerned with taking product shots in focus for my site. > So an out of focus shot at the distance calculated is going to be what you > get, that's simple. Eh? >> A direct experiment is the quickest way to find out. >> [quoted text clipped - 19 lines] >>>I really am only concerned with taking product shots in focus for my >>>site. >>So an out of focus shot at the distance calculated is going to be what you >>get, that's simple. > > Eh? Hmm, so not that simple? I thought I could figure the dioper strength as with your example for the lense that normally focuses to 7.5 feet, the +2 diopter lets it get to 16 inches so one could just hold that lens 16 inches away & see the field of view (even though it's badly out of focus without the diopter. Is that too simple? I actually don't have that lens yet, I have a smaller slower 200mm that goes to about 16 inches without the diopter so the diopter on the fast 7.5 foot lens would be the same as my current lens (I think). > +2 means it has a focal length of 1/2 meter. This is a diopter unit > (reciprocal focal length) as used in eyeglass prescriptions. [quoted text clipped - 20 lines] > > That's how close you can get. >>>A direct experiment is the quickest way to find out. >>> [quoted text clipped - 4 lines] >>>away from the film, but lets you get an in-focus image of a nearer >>>subject. That's the simplest way to approach the calculations. |
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