how to determine feet as it relates to mm in photography. idont understand and cant find this answer anywhere that i can understand

Question

how to determine feet as it relates to mm in photography.

Answer 1

Hi Theresa –

I think there may be two questions going on here, and I will attempt an answer as such.

The first question (and one that may not be very satisfying), is what does mm mean? This is a technical thing, referring a distance inside the camera, specifically the distance between the lens and the focal plane when the lens is focused on infinity.

The second question (and I think this is getting to heart of it), is what does the mm say about what is going to be in the field of view? The smaller the number, the wider the angle of view.  On a 35mm sensor, a 14mm lens will capture 114 degrees, whereas a 500mm lens will capture a very narrow 5 degree field of view.  A good illustration of this is posted at http://www.digitaltechnologyart.com/angle-of-view.html.

Once you decide what you want in your frame, your choice of focal length will have a big impact on how your image looks. Say you want a headshot, capturing your subject from the collar bone to just above the hairline. With a wide angle lens, you’d have to stand very close to your subject to get that crop. You would capture your subject and a lot of the background on either side, and your subject would be very distorted – with the parts nearest the camera, such as the nose, looking disproportionately large and those further away, such as the ears, looking quite small. Not likely a flattering shot.

Shooting with a longer focal distance, such as in the 85-135mm range, will force you to back away from the subject to achieve the desired crop (collar bone to above hairline, in this example), and in backing away, the distortion will be significantly reduced. You’ll also have a narrower angle of view, meaning less width of the background will be shown, making easier to find a non-distracting sliver of the background to include.

 

There’s a great tool posted at dofsimulator.net that illustrates these concepts, as well as the effect on the background blur: http://dofsimulator.net/en/.

 

Hope that is helpful. 

 

Cindy

Answer 2

Would need some clarity on the question as it relates to photography. 

    But I am assuming that you are referring to mm as in Focal length of the lens i.e 24mm lens

    I am also assuming that distance as in feet would be the relationship of how far you can be away from your subject.

I am not aware of a particular formula that would calculate the Best focal length at a given distance BUT

   If you consider that focal length  as in wide vs telephoto is based on normal Eyesight being 50mm

    So at 100mm focal length would be 2x magnification of Normal sight. The Subject would appear ½ the distance or twice as close as normal (50mm) sight

      You can use this as a rule of thumb   If a subject is 50 feet away at 50mm then the subject would appear 25ft away at 100mm 

     Hope that helps 

Answer 3

I'm not sure if I fully understand the question. I think you may be asking about the Minimum Focus Distance for a lens at a specific MM.

 

The most basic explanation is what you are trying to focus on must be "X" number of feet away from the lens to be able to focus. A lens/camera can't focus on an object that is too close to the lens.

 

The number varies for different lenses and at different MM. Most if not all lenses have guides on the lens as a reference, or at the very least, it will be explained in the manual. An "in the field" solution to focusing problems is to step back a little and try focusing again to prevent being too close to subject.

Answer 4

Dear Theresa,

 

There are 25.4 mm per inch or (12)*(25.4)mm per foot.

 

(12 inches/foot)*(25.4 mm/inch) = 304.8 mm/foot.

 

I don't know if that answers your question or not.