What size print for life size image?

[markperez]

If I take a photo of a shoe at 50mm with a D70 from say 3 feet away what size print would I need to have it printed as a life size image?

[Michelle Allmon]

Why don't you take the picture, measure the shoe, make a save as copy and crop it in to the edges of the shoe and resize it to print size that matches the shoe measurement and then go from there?

[markperez]

Yeah that is the way I figured I would have to do it but I thought there might be some sort of calculation that I might be able to do. Thanks for your suggestion.

[Michelle Allmon]

Figure it out and post it for us hehe! Thanks in advance!

[Michelle Allmon]

You could also do it backwards, like if you are planning on making an 8x12 and the shoe is 10", eyeball it when you shoot it. That's how I did passports on film, I would figure the head needs to be one inch, it'll be printed 2x3, so my head needs to fill exactly 1/3rd of the frame.

(vertical)

[Stephen H]

Okie doke, first rule is that 1/SD + 1/FD = 1/FL, where SD = subject distance, FD = distance from film to lens nodal point (I'm a film guy), and FL = focal length.

Second rule is that when the lens is focused, the geometry is the same as in a pinhole camera, meaning you have some similar triangles to work with.

So, assume nodal point to shoe is 36" and shoe is 12" long (big feet here). SD = 36"x25.4mm/in = 914mm, FL = 50mm, so FD = 52.89 mm.

Then image ratio to object size is 52.89/914, so 12" shoe is 0.694" = 17.64 mm. To blow it up to life size is 12 x 25.4/17.64 = 17.3X enlargement. I find the sensor size on a D70 is 23.7mm, so that equates to a 16.12" long image.

This would be approximate because you generally don't know the exact nodal point of the lens, so you can't figure the nodal point-to-subject distance exactly. But close enough.

[huxley]

Originally Posted by Stephen H

Okie doke, first rule is that 1/SD + 1/FD = 1/FL, where SD = subject distance, FD = distance from film to lens nodal point (I'm a film guy), and FL = focal length.

Second rule is that when the lens is focused, the geometry is the same as in a pinhole camera, meaning you have some similar triangles to work with.

So, assume nodal point to shoe is 36" and shoe is 12" long (big feet here). SD = 36"x25.4mm/in = 914mm, FL = 50mm, so FD = 52.89 mm.

Then image ratio to object size is 52.89/914, so 12" shoe is 0.694" = 17.64 mm. To blow it up to life size is 12 x 25.4/17.64 = 17.3X enlargement. I find the sensor size on a D70 is 23.7mm, so that equates to a 16.12" long image.

This would be approximate because you generally don't know the exact nodal point of the lens, so you can't figure the nodal point-to-subject distance exactly. But close enough.

um ok clear as mud. feel like im back in high school taking the S.A.T. eeeeessshhhhh

[venchka]

You could take a picture of a ruler with the numbers parallel to your sensor of choice. Enlarge the print until it matches the original.

[CaptainTom]

Originally Posted by Stephen H

Okie doke, first rule is that 1/SD + 1/FD = 1/FL, where SD = subject distance, FD = distance from film to lens nodal point (I'm a film guy), and FL = focal length.

Second rule is that when the lens is focused, the geometry is the same as in a pinhole camera, meaning you have some similar triangles to work with.

So, assume nodal point to shoe is 36" and shoe is 12" long (big feet here). SD = 36"x25.4mm/in = 914mm, FL = 50mm, so FD = 52.89 mm.

Then image ratio to object size is 52.89/914, so 12" shoe is 0.694" = 17.64 mm. To blow it up to life size is 12 x 25.4/17.64 = 17.3X enlargement. I find the sensor size on a D70 is 23.7mm, so that equates to a 16.12" long image.

This would be approximate because you generally don't know the exact nodal point of the lens, so you can't figure the nodal point-to-subject distance exactly. But close enough.

This calculation works well with rhumboid subjects, but with anterior configured objects you have to calculate the quantum distance and deal with the cosine of the tangent. Assuming you have the exact nodal point located, you could always stimulate the axial progression until you can accurately predict the hyperfocal dimension. With mens shoes, the formula can be inversed and the determining factor is shoe color.

[venchka]

[huxley]

anyone have a darn chart to look at. say a 12inch object (rough head size) 3 ft away with fixed focal lengths of 35 and 50 mm?

[Stephen H]

Let's simplify this:
Question: If I take a photo of a shoe at 50mm with a D70 from say 3 feet away what size print would I need to have it printed as a life size image?

Answer: About 16" long print.

[Stephen H]

PS.

Q. If a hen and a half can lay an egg and a half in a day and a half, then how many gophers can a monkey with a wooden leg stomp?

A. False. Footballs don't have feathers.

[Wes]

Wrong. The answer is 1.21 gigawatts. That's what you're gonna need for your Flux Capacitor.

[markperez]

Stephen thanks for the in depth answer
LOL thanks everyone else for the laugh