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06-10-2008, 11:54 AM   #16
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QuoteOriginally posted by ftpaddict Quote
On a full frame/35mm film camera, being able to focus on a ruler and get close enough to only be able to capture 36mm along the horizontal line of the frame equals 1:1 magnification (because FF means roughly 36mm horizontally and 24mm vertically). You can do the math from there.
I understand that.
What I meant to ask was whether there is a way to figure out mag ratio just by knowing the optical specs of the lens. Without doing the focus testing and such.

06-10-2008, 12:51 PM   #17
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QuoteOriginally posted by TimB Quote
Is there a way to calculate the mag ratio from focal length, focus distance, etc.?
It seems like it should be possible, but I can't figure out how.
there is I have them somewhere, but generally, it is the ratio of lens to subject distance over lens to film distance.

when the two are equal you get 1:1.

If you know the focal length of the lens, and the close focusing distance you should be able to calculate it.

I will look as I have the formulas somewhere
06-10-2008, 02:51 PM   #18
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QuoteOriginally posted by Lowell Goudge Quote
I will look as I have the formulas somewhere
Yes... I love formulas
06-10-2008, 02:52 PM   #19
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QuoteOriginally posted by Lowell Goudge Quote
I will look as I have the formulas somewhere
I feel a headache coming on!

06-10-2008, 03:18 PM   #20
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QuoteOriginally posted by ftpaddict Quote
I feel a headache coming on!
Hah, I should add a disclaimer to the thread that readers may experience some discomfort in the general brain area.
06-10-2008, 04:36 PM   #21
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I would agree with the consensus that by definition macro is 1:1 but 1:2 is good enough. I think that 1:3 is stretching it though and would really wish that vendors with 1:4 and 1:5 magnification would say "close focus" or something instead.

As far as formulas go (rustling sound of web pages being turned)...

If you are using an extension tube magnification ratio = extension length / lens focal length, so a 50mm extension on a 50mm lens should get you 1:1. The longer the extension tube the greater the ratio, as you'd expect. I think it's a 2 stop loss of light in that case.

You can also mount a reversed lens on a main lens using a "macro coupling ring" (double threaded male). The main lens is mounted on the camera normally. The resulting magnification ratio = main lens focal length / reversed lens focal length, so the shorter the reversed lens the greater the magnification. I have used a 28mm on my FA77 (surely an abuse of that lens!) which got 2.75x.

The Vivitar 2x Macro Focusing Tele Converter (AKA V2XMFTC) turns any attached lens into a macro. The longer the lens, the more the magnification, but I am not sure of the exact formula. I think it's the same as the extension tube one above, so a 50mm gets you 1:1 and the 77mm gets approximately 1:1.5.

Not sure where I got this info from, but I did do quite a lot of reading and experimenting. Now I own two 1:1 lenses plus a 1:3 that claims macro and a V2XMFTC plus reversing rings. That might be enough.
06-10-2008, 04:38 PM   #22
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QuoteOriginally posted by TimB Quote
Hah, I should add a disclaimer to the thread that readers may experience some discomfort in the general brain area.
Actually, I started with a headache but it's clearing up now.
06-10-2008, 04:53 PM   #23
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QuoteOriginally posted by rparmar Quote
Actually, I started with a headache but it's clearing up now.
In that case I should start charging people.

06-11-2008, 06:24 AM   #24
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QuoteOriginally posted by PentaxPoke Quote
Hey Mike, that Tak is starting to rust! (or maybe that is some other gunk)
It is considered ungentlemanly to call attention to a lady's liver spots.
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