Close-up, Macro, Micro Calculations

[xkaes]

I know I am wading into the swamp. But I've done that since I was a kid, so no amount of MUUUUDDDD will bother me. I've seen it all.

Several people on several board have basically asked a simple question. Admittedly, they asked it in several ways which has just made matters worse -- trying to figure out what they mean.

The question is "Is there a SIMPLE way to determine the amount to adjust the f-stop of a lens if - If - IF you know the magnification?"

First, this question is IF you know the magnification, so there is no need to respond by telling us how to determine the magnification.

Second, this question is how much to adjust the aperture -- not a calculation about how to adjust a SPECIFIC f-stop. In short, +1/3 f, or +2 3/4 f, etc.

Here is a real number chart of how much you need to adjust the f-stop based on the magnification.



You might want to print this out for your use on a sheet of paper or a business card.

It seems like a pretty smooth curve, but when I try to compute the formula for the line/curve the best I can do is a cubic formula.



It's close, but not as close as I would like.

There has to be a better formula to compute f-stop adjustment based on magnification.

Is there one?

Let's stick to this simple question, OK?????

IF I KNOW THE MAGNIFICATION, HOW DO I DETERMINE THE AMOUNT TO ADJUST THE f-STOP????

[Bob Salomon]

1:1 = 2 stops; 2:1 = 4 stops, etc.. 1:2 = 1 stop; 1:4 = ½ stop; etc..

[Dan Fromm]

Just calculate effective aperture from aperture set, pupillary magnification and magnification. m stands for magification, p for pupillary magnification.

For an asymmetrical lens (triplet, Tessar, ...) with the lens facing normally,

effective aperture = aperture set * ((m/p) + 1)

For an asymmetrical lens (triplet, Tessar, ...), with the lens reversed,

effective aperture = aperture set * (1/P) * (1 + P*M)

For a symmetrical lens (dialyte, dagor, plasmat, ...),

effective aperture = aperture set * (1 + m)

I don't think in terms of adjustment, I think in terms of "if this is what I set, that is what I'll get." If I needed to think in terms of "if I work at this here magnification and the meter says f/whatever, which f/stop should I set?" I'd rearrange the equation.

Oh, and by the way, Joe, if you want to learn how to think about closeup work, buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography. Available at reasonable prices from used bookstores that offer their wares on abebooks.com, alibris.com, amazon.com, bn.com, ... Touted in my list of useful links.

[xkaes]

Oh, and by the way, Joe, if you want to learn how to think about closeup work, buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography. Available at reasonable prices from used bookstores that offer their wares on abebooks.com, alibris.com, amazon.com, bn.com, ... Touted in my list of useful links.

Yes, I have a copy of Lester's book, but neither you nor he has a simple formula X (f-stop adjustment) for magnification.

[xkaes]

1:1 = 2 stops; 2:1 = 4 stops, etc.. 1:2 = 1 stop; 1:4 = ½ stop; etc..

Great. So what is the formula????????? I've already plotted it out.

I'll be glad to give you the best formula that I have -- it's cubic. I would like to know yours.

[xkaes]

Just calculate effective aperture from aperture set, pupillary magnification and magnification. m stands for magification, p for pupillary magnification.

For an asymmetrical lens (triplet, Tessar, ...) with the lens facing normally,

effective aperture = aperture set * ((m/p) + 1)

For an asymmetrical lens (triplet, Tessar, ...), with the lens reversed,

effective aperture = aperture set * (1/P) * (1 + P*M)

For a symmetrical lens (dialyte, dagor, plasmat, ...),

effective aperture = aperture set * (1 + m)

I don't think in terms of adjustment, I think in terms of "if this is what I set, that is what I'll get." If I needed to think in terms of "if I work at this here magnification and the meter says f/whatever, which f/stop should I set?" I'd rearrange the equation.

Oh, and by the way, Joe, if you want to learn how to think about closeup work, buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography. Available at reasonable prices from used bookstores that offer their wares on abebooks.com, alibris.com, amazon.com, bn.com, ... Touted in my list of useful links.

I don't care about "aperture set" or "effective aperture". I care about "aperture adjust" amount.

I don't want to rearrange the equation. The question is straightforward and simple -- and many people want to know.

At a given magnification, how much do I adjust the aperture in f-stops? How can I compute this? This is the 21st century afterall.

[Tin Can]

I bought the Lester book on Dan's recommendation some years ago.

Very interesting, as they say.

I calmly read it.

Just calculate effective aperture from aperture set, pupillary magnification and magnification. m stands for magification, p for pupillary magnification.

For an asymmetrical lens (triplet, Tessar, ...) with the lens facing normally,

effective aperture = aperture set * ((m/p) + 1)

For an asymmetrical lens (triplet, Tessar, ...), with the lens reversed,

effective aperture = aperture set * (1/P) * (1 + P*M)

For a symmetrical lens (dialyte, dagor, plasmat, ...),

effective aperture = aperture set * (1 + m)

I don't think in terms of adjustment, I think in terms of "if this is what I set, that is what I'll get." If I needed to think in terms of "if I work at this here magnification and the meter says f/whatever, which f/stop should I set?" I'd rearrange the equation.

Oh, and by the way, Joe, if you want to learn how to think about closeup work, buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography. Available at reasonable prices from used bookstores that offer their wares on abebooks.com, alibris.com, amazon.com, bn.com, ... Touted in my list of useful links.

[xkaes]

Let's stick to this simple question, OK?????

IF I KNOW THE MAGNIFICATION, HOW DO I DETERMINE THE AMOUNT TO ADJUST THE f-STOP????

Can we?

[Dan Fromm]

Joe, most LF lenses are symmetrical. For them, if the meter says "use f/x", calculate the stop to set as aperture to set as aperture recommended/(1 + m). That's all. If the meter says use f/16 and magnification is 1, aperture to set = 16/2 = 8. You can do the arithmetic in your head.

If you don't want to do this kind of arithmetic, get a Horseman meter. For 4x5 a 4x5er will give better results than a 2x3er in an adapter.

If you must do things your way, learn about logarithms. AND DON'T YELL AT ME!

[Bob Salomon]

Can we?

That is what my response told you!