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09-01-2008, 06:23 AM   #1
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Help with closeup lens filters

Hello:

Newbie here! Can someone explain to me how the closeup lens filters are supposed to work. Like, do you have to get right up on whatever you are trying to photograph? Is the auto focus supposed to work?

Also, what does the focal length mean on a macro lens (90 vs 105, etc). Is the higher the number the further away you can get and still get an up-close focus?

Tks for the help!!!!!!!

ctt

09-01-2008, 06:44 AM   #2
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QuoteOriginally posted by ctt Quote
Newbie here! Can someone explain to me how the closeup lens filters are supposed to work. Like, do you have to get right up on whatever you are trying to photograph? Is the auto focus supposed to work?
i don't have one but i think AF should work, everything is just magnified. i'm not sure how close you have to get.

QuoteOriginally posted by ctt Quote
quAlso, what does the focal length mean on a macro lens (90 vs 105, etc). Is the higher the number the further away you can get and still get an up-close focus?
yes, the minimum focusing distance will be a bit longer giving you more working room for lighting and not scaring away the creatures
09-01-2008, 05:19 PM   #3
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QuoteOriginally posted by ctt Quote
Hello:

Newbie here! Can someone explain to me how the closeup lens filters are supposed to work. Like, do you have to get right up on whatever you are trying to photograph? Is the auto focus supposed to work?

Also, what does the focal length mean on a macro lens (90 vs 105, etc). Is the higher the number the further away you can get and still get an up-close focus?

Tks for the help!!!!!!!

ctt
close up filters are usually marked in terms of diopters.

for your benefit, a diopter is 1/focal length (of the filter) in meters.

Therefore, 1 diopter is a 1 meter focal length, 2 diopters is 1/2 meter focal length etc.

they work as follows. by attaching one to your lens they modify the maximum focusing distance to their own focal length, therefore with a 1 diopter lens, you will be working between 0 and 1 meter, a 2 diopter means you will be between 0 and 1/2 meter.


With respect to focal length on macros, they mean the length of the lens when focused at infinity. the longer the focal length, the bigger the image, for any subject at the same distance for the two lenses.

One thing to remember with macro is that you achieve 1:1 when the image distance is equil to the lens to focusing plane distance, and to achieve this with macto, means you need to be 2 times the focal length away from your subject. as you can see the 105 mm lens would achieve this with the subject further away. while this may not always be important, sometimes it is difficult to get close and still properly light your subject, or the subject won't allow you to get close
09-01-2008, 05:39 PM   #4
ctt
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Original Poster
When looking at the specifications of a macro lens, is it important to look at the minimum focus distance? I'm looking a lens that has 11.93 inches under minimum focus distance on a 100mm f2.8 lens. That seems like you have to pretty far (almost a foot away?)) Am I reading that correctly?

Tks!

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