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hellerharris · Joined: 27 Jun 2002 Posts: 46 Location: Los Angeles

Anyone know of a focal length equivalence chart that includes 3X4 size negatives?

thanks in advance.

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F1-86

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

Using the "focal lenght of a normal lens is equal to the diagonal of the format" rule

the true normal lens for 35mm is 62mm,. The normal lens for 3x4 is 135.89mm.
sqrt of [(3.25)2]+[(4.25)2] x 25.4mm

If you divide 135 by 62 you'll get 2.17. Now multiply any focal lenght lens from your 35mm by 2.17 and you'll get the equivelent focal lenght in 3x4

If you want to compare 3x4 to 4x5, then you'll need to find the diagonal of 4x5 sqrt(a^2+b^2)
and go from there

AWT · Joined: 05 Sep 2002 Posts: 57 Location: Upstate SC

Um, Les...

Isn't the true normal lens for 35mm closer to 43mm?

The 35mm negative is 24mm x 36mm. The diagonal would therefore be the square root of [(24*24)+(36*36)] or 43.27mm.

That being said, dividing 135 by 43 would yield 3.14, the factor you'd want to multiply a 35mm lens by to get the equivalent in 3x4 lenses.

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

Damn! foisted on my own slide rule! yes you are right it's 43mm not 62mm.

Les

km · Joined: 05 Oct 2002 Posts: 10 Location: Northern Indiana

LOL Les, I ain't the only old guy who still owns a slide rule. but we both may be forgeting how to use one.

thanks for all your informative posts.

Keith

Dan Fromm · Joined: 14 May 2001 Posts: 2159 Location: New Jersey

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

Now if he had a 6" circular ruler he could have brought that out two more digits!

The slide part I remember, it's what to do with all those tiny marks that give me fits!

[ This Message was edited by: Les on 2002-12-30 17:55 ]

45PSS · Posted: Tue Dec 31, 2002 7:06 am Post subject:

Sq.Rt.[{4x25.4}2 +{5x25.4}2]
sq.rt.[{101.6}2+{127}2]
sq.rt [10322.56+16129]
sq.rt.[26451.56]
=162.63935
or
sq.rt.[{4}2+{5}2]x25.4
sq.rt.[16+25]x25.4
sq.rt.[41]x25.4
6.4031242x25.4
=162.63935

4 X 5 "normal" 162mm
divided by 35mm "normal" of 43mm
=3.7674418 or 3.77

3.77x43=162.11

Basic math formulas and electric caculator!
All steps shown for the benefit of those that need them.

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hellerharris · Joined: 27 Jun 2002 Posts: 46 Location: Los Angeles

Forget the arithmetic; the principle is just a linear comparison of diagonal of the film frame, right?

The slide-rule stories are a little scary.

thanks,
Heller

________
marijuana seeds

Dan Fromm · Joined: 14 May 2001 Posts: 2159 Location: New Jersey

Nick · Joined: 16 Oct 2002 Posts: 494

"Back to slide rules. What I found astonishing was that my instructor, a PhD economist with a masters in engineering, had lost the idea of doing arithmetic in his head."

Well I think most kids today have to. When I went to school we were near the dividing line. We weren't allowed to use calculators or any other device the kids a few years behind us got allowed anything short of a cray computer-)

I still think it hurt them more then it hurt us. I can easily function using my head,paper or even my toes.

45PSS · Posted: Wed Jan 01, 2003 6:34 am Post subject:

I just used the caculator as it is faster and less likely to be questioned here. My math is a little rusty but still there.
2+2 is still equal to 3.97835 plus or minus .001 isn"t it?

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[ This Message was edited by: 45PSS on 2002-12-31 22:35 ]