Math help please

[jwcat]

First let me site my sources. I watched the following article at:
http://figitalrevolution.com/2009/0...r-leica-zeiss-xa-lca-rollei-lomo-diana-holga/ . He referenced the following page:

http://www.tomchuk.com/rf_hfd/ (human rangefinder)

On further digging I came up with this:

http://photo.net/minox-camera-forum/003HEV (rangefinder for minox)

I would like to find a formula to solve for distance when base (eye spacing) and arm extension are given, using a hypothetical ruler to determine displacement of target at arm extension distance.

Figure eye distance, arm extension (one time measurements) and by using the one eye closed method, measure the image displacement. Plug displacement into formula and determine target distance. I have been digging around math and trig sites but none have shown solutions for my problem.

My last formal math course was well over 40 years ago and I am sadly lacking the skills.

I put this in off-topic even though it involves rangefinders and cameras so as not to annoy serious people.

Thanks...John Cates

 

[ebolton]

I can help you with that. The math isn't really more than basic geometry and algebra.

If you make a little diagram illustrating a top view of the problem, you can see it is a case of similar triangles.

Distance to target is D
Eye base is B
Arm extension is d
Image displacement is b

Triangle of base B and height D is similar to triangle of base b and height (D-d).

Solution after some algebra is

D = d/(1-b/B)


-Ed

 

[ebolton]

 

[jwcat]

Thank you very much. I may print out your signed artwork for framing.

John