Hammer Loc: London UK

Feel stupid asking this . Is there any formula that can be applied to determine an optimum focal length for a lens when the size of the object and distance to the object are known and the intention is to fill the frame on say a full frame sensor.

Lay in, I can take it.

CHG_CANON Loc: the Windy City

Experience, both in general and with the specifics of your own equipment. I've found you also develop your own preferred perspective, well I have at least. If you analyze your images, you can even see / detect this preference. For example, with a zoom lens covering 70-200, I've noted I tend to shoot around 135 within that range. I could step closer or back or zoom wider or closer, but my preferred perspective tends to be a distance where a 135mm focal length is best. Looking at the focal length of the images in Lightroom revealed this detail.

Look at your own work with a critical eye and knowledge of the shooting and editing. Do you need more focal length for the images you desire? Do you show up at a shoot with the wrong lens(es) in the bag? A bit of introspection is probably all that is needed, not an app for that ...

jerryc41 Loc: Catskill Mts of NY

When I bought my cameras, I had them modified so that the frame is always full.

Actually, I like to leave a little room around the edges for cropping and printing. Different size prints require different cropping, and I'd rather not cut out part of the picture.

Electric Gnome Loc: Norwich UK

I expect there is, or could you make a card cutout of the intended subject (hope it's not a saturn 5) and shoot at the intended distance with a couple of lenses to establish the correct focal length, if there is no other way.

boberic Loc: Quiet Corner, Connecticut. Ex long Islander

The simple truth is, I am just not good enough to "fill the frame" for every contingency. I like to leave a little "around the edges" to cover my "asss" in various conditions

Linda From Maine Loc: Yakima, Washington

An interesting question, but seems to address prime lenses exclusively.

With my APS-C Canon T3i, I found an 18-135 mm to be highly versatile, and with my MILC Panasonic, similarly it's my 14-140 mm. That range allows for wider viewpoints or filling the frame with most subjects I'm interested in shooting. A zoom also gives you the flexibility mentioned here by others about leaving a little around the edges in case you want to print a different aspect than 3:2.

Burtzy Loc: Bronx N.Y. & Simi Valley, CA

The size of the object can vary. It can be from something very small to something very large, even if the distance stays the same. So a formula can't apply. So the most usable solution, is to use your eye and determine if the lens is the right one. If you have too wide-angle a lens, the image will appear distorted. To long a focal length and you could inadvertently crop your subject. If you are unable to do that, then changing the distance is your other option. But if that is impossible, then a zoom lens would be the only other solution. Generally, a portrait-length setting...roughly double the "normal" length... will give you a filled frame, un-distorted image. For example, in a Full Frame camera, 50mm is considered normal. So a focal length off about 100mm will not give a distorted view. But as to a formula, not likely...too many variables.

Blair Shaw Jr Loc: Dunnellon,Florida

You'll know it when you see it I always say.......and there are formulas for angles of view but some lenses have sweet spots and you just have to determine which ones serve your intentions best. You're the Master of Your Disaster .......Good luck Hammer

Silverrails

Longshadow Loc: Audubon, PA, United States

That's why I like zooms.
Compose (adjust), shoot.
No measuring or calculating involved.
I like to keep things simple.

jayluber Loc: Phoenix, AZ

Simple answer - yes. The angle of the lens - coupled with the distance to subject and dimensions of the subject will let you know how far away to be to fill the frame. You'll have to use a trig table or figure it out with a pencil.
Whether you want to fill the frame is a totally different issue.

User ID

My method is only mildly mathematical and based on similar triangles ... but there is NO trigonometry to calculate.

The examples are for FF but for any other formats you do need to know the length of your sensor in mm. Use 35mm for FF, 24 for APSC and 17 for m4/3.

OK ! Here’s the deal. The foundation is the view of a 35mm lens. Magic is due to the lens mm being the same as the sensor mm, 35 for each. The result of that matchup is THIS matchup:
The width of the real world scene is the same as the distance to that scene. IOW if the subject is 10 paces away the scene is 10 paces wide at the subject.

If the background is the horizon then it’s about 12 miles away so you will include a 12 mile stretch of horizon ... that same matchup, distance equals width.

Now for other lenses than the 35. How bout a 17mm UWA ? Well 17 is HALF of 35, so distance this time is HALF of the scene width (scene width is TWICE the subject distance.)

If the above is clear to you then it should clear that for a 100mm lens the scene width is 1/3 of the subject distance cuz 35 is 1/3 of 100.

Just to add a few easy examples:
For 350mm lens, the side of one car will fill the frame if you shoot from 10 car lengths away. Bonus points if it occurs to you that if the horizon is visible (12 miles away) you’ll get a 1.2 mile stretch of it in the frame.

For a 24mm lens (2/3 of 35mm) the subject distance is 2/3 of the scene width. Flip the camera to portrait and shoot a half-length portrait from about 2 feet away .... guessing that a half person is about 3 feet height-wise. (2 feet, 3 feet, “2/3” ..... got it ?)

jayluber Loc: Phoenix, AZ

Just remember the great Indian Chief: SOH CAH TOA

For example a 4 Degree lens at 50' will capture an object aprox 3.5' wide

Ysarex Loc: St. Louis

Where F = focal length, D = lens/subject distance, S = the linear size of the subject, and N = length of the negative: F = (N/2)/tan(arctangent((S/2)/D))

Joe

jayluber Loc: Phoenix, AZ

and a 24 deg lens will capture aprox 20' at a distance of 50'
That assuming FF lens for FF camera and Crop for crop.
If FF lens on crop - need to adjust angle for crop factor.