Geometry Question: Trying to prep Lam needed lenses for a trip. If you know the shooting distance and the width of the subject you want to capture, what is the easiest way to calculate...

John Howard Loc: SW Florida and Blue Ridge Mountains of NC.

Trying to prep Lam needed lenses for a trip. If you know the shooting distance and the width of the subject you want to capture, what is the easiest way to calculate the lens length. The angle of view is in the camera spec. I forget my trig and how to use the angles and one side to calculate the other side. I want to calculate for 100 yards for each lens and then can use likely shooting distance to calculate the width.

davidf_logan Loc: Logan, Utah

Does these help?

https://www.lensation.de/calculator.html (this seems to not do FF sensors)

http://www.giangrandi.ch/optics/focalcalc/focalcalc.shtml

RichardTaylor Loc: Sydney, Australia

Try the domensional FOV calculator here:

https://www.tawbaware.com/maxlyons/calc.htm

Rongnongno Loc: FL

John Howard wrote:

Trying to prep Lam needed lenses for a trip. If you know the shooting distance and the width of the subject you want to capture, what is the easiest way to calculate the lens length. The angle of view is in the camera spec. I forget my trig and how to use the angles and one side to calculate the other side. I want to calculate for 100 yards for each lens and then can use likely shooting distance to calculate the width.

Personally I would not use a calculator but determine first what perspective I need.

Selecting a lens implies many things including compression (long lens) distortion (wide angle) and whatever each lens adds or subtract to the previous two.

I select my lens depending one what I really need, not in function of a math formula. My feet work relatively well so that is what I use... Now if this is not possible there is very little advantage to use a fixed lens so a zoom would work w/o the math headache (I hate math).

Just my opinion, not an answer to your question.

bleirer

John Howard wrote:

Trying to prep Lam needed lenses for a trip. If you know the shooting distance and the width of the subject you want to capture, what is the easiest way to calculate the lens length. The angle of view is in the camera spec. I forget my trig and how to use the angles and one side to calculate the other side. I want to calculate for 100 yards for each lens and then can use likely shooting distance to calculate the width.

Calculator here includes adjustment for sensor size. https://www.cambridgeincolour.com/tutorials/camera-lenses.htm

Notorious T.O.D. Loc: Harrisburg, North Carolina

The Photo Pills app includes a FOV calculator also as part of its toolset.

BboH Loc: s of 2/21, Ellicott City, MD

John Howard wrote:

. The angle of view is in the camera spec. .

Bye the way, John, the angle of view is NOT in the camera but the lens. If you have the manual for the lens it will state the angle of view in the tech specs.

Jerry G Loc: Waterford, Michigan and Florida

It's a simple geometry formula, S/F=s/d. Sensor width/Focal length= subject width/distance.

John Howard Loc: SW Florida and Blue Ridge Mountains of NC.

Fair point. And would be right if shooting at home. I am trying to determine which lenses to take on a trip with me. I am using Google Earth to spot my locations and subjects, and can measure distance/size. A bit of a theoretical exercise.

John Howard Loc: SW Florida and Blue Ridge Mountains of NC.

Jerry G wrote:

It's a simple geometry formula, S/F=s/d. Sensor width/Focal length= subject width/distance.

Really? ie, 35mm FF / 50mm lens = view width / distance to subject
OR 35/50 = Width/100m
.7 = Width / 100m
.7x100 = Width
70m = Width

So a 50mm lens will capture a view of 70m wide if 100m from the subject.

Is that it?

John Howard Loc: SW Florida and Blue Ridge Mountains of NC.

Thanks. Will give it a test run.

John Howard Loc: SW Florida and Blue Ridge Mountains of NC.

BboH wrote:

Bye the way, John, the angle of view is NOT in the camera but the lens. If you have the manual for the lens it will state the angle of view in the tech specs.

Yes. I mis-typed.

CatMarley Loc: North Carolina

John Howard wrote:

Trying to prep Lam needed lenses for a trip. If you know the shooting distance and the width of the subject you want to capture, what is the easiest way to calculate the lens length. The angle of view is in the camera spec. I forget my trig and how to use the angles and one side to calculate the other side. I want to calculate for 100 yards for each lens and then can use likely shooting distance to calculate the width.

Get a sine /cosine table - you may have the function on a calculator - I do on my Texas Instrument calculator. Tan x = a/b where x is the angle, a is the width of the subject and b is the distance.

Jerry G Loc: Waterford, Michigan and Florida

John Howard wrote:

Really? ie, 35mm FF / 50mm lens = view width / distance to subject
OR 35/50 = Width/100m
.7 = Width / 100m
.7x100 = Width
70m = Width

So a 50mm lens will capture a view of 70m wide if 100m from the subject.

Is that it?

That is the formula used in the Navy to determine what camera, lens and altitude to use for aerial photography. Your math seems correct.

Mercer Loc: Houston, TX, USA

A super-good source for nearly all things math is "Mathematics for the million" by Hogben and inexpensively available from Amazon.

It's not only a great read, but has extensive applications with well explained instructions for trig. It covers the history of mathematics from ancient times through Newtonian calculus, and does it in such a manner that it is a fascinating story. If you like numbers, you'll have fun with this book.