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How far do I need to be in order to take an actual size photo of an object that's 6.25 inches by 6.25 or, if you prefer; 158.25mm X 158.75mm?

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    \$\begingroup\$ The question does no make much sense. The size of an image of an object is depending on the distance, the focal length of the lens and the crop factor of the camera. The size of the print is depending of how big you choose to print it. If you want to have a true 1 to 1 image, you would need to have a sensor that big. Can you clarify your question? \$\endgroup\$ Commented Feb 20, 2020 at 10:20
  • \$\begingroup\$ I'm obviously no photographer and I also obviously don't know much about the subject. It's 3 AM and I am trying to fix my vinyl floor in a few spots. I've done something similar before but I didn't have to print the photo it was already printed. Need the same design as is there now or I have a major project on my hands and I'm disabled caring for an elderly parent. I don't have the means to do the entire floor. \$\endgroup\$ Commented Feb 20, 2020 at 11:01
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    \$\begingroup\$ In order to answer your question we need to know what camera you are using so that we know the sensor's size, the lens focal length you are using, and the size that your print will be made. \$\endgroup\$
    – Michael C
    Commented Feb 20, 2020 at 11:30
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    \$\begingroup\$ @Mr.Flowerz while the details in your comment may make people more willing to help you, without the hard numbers people have asked for, no one is able to help you \$\endgroup\$
    – Chris H
    Commented Feb 20, 2020 at 15:36

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I am trying to fix my vinyl floor...

Sounds like it would not ruin the aesthetics of your photos if you laid a ruler on the floor, and included it in the frame when you took the picture.

My own next step* would be to open the original in an image editor (e.g., https://www.gimp.org/). I would use the editor to measure how many image pixels per inch-of-ruler, and I would save a copy that declares itself to have that many pixels per inch of paper.

I would expect to get an actual-size printout when I sent the copy to my printer, and I could easily verify that by comparing the ruler in the picture to the actual ruler. If I missed the mark, I could calculate how much bigger or smaller to make the printout, and I probably would nail it on the second try.


* But, learning to edit photos may not be something that you'll master in a single sitting. At least, you'll have the ruler in the photo to show the true scale, and maybe that could reduce the number of rounds of trial-and-error you'll need if you insist on having a truly 1:1 printout.

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    \$\begingroup\$ If you have picture of subject & ruler, next might be to take it to friendly printer & explain... \$\endgroup\$
    – Tetsujin
    Commented Feb 20, 2020 at 16:09
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You are talking about imaging at "unity" i.e. life size - magnification 1.

When the camera is focused at infinity, meaning as far as the eye can see, like distant mountains or stars, the lens-to-film or lens-to- image sensor distance will be the same as the focal length. When imaging nearby objects, to focus the lens will racked forward, away from film or image sensor by a few millimeters.

When we image at unity 1:1 magnification life-size, the focused lens will be 2X (two times) the focal length forward. The distance film or sensor-to-object will be 4X the focal length.

Suppose you mount a 100mm focal length lens and image an object to obtain "unity". The distance, object to sensor/film will be 400mm. The lens will be positioned in center of this span.

Note: The measuring point for the lens likely will not fall at the center of the lens barrel. We measure from a cardinal lens point called the rear nodal. This point, depending on lens design, can be shifted for or aft of the center of the lens array.

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  • \$\begingroup\$ Your answer tells how to control the size of the image that falls on the camera sensor, but the OP is asking how to control the size of the image in a final, paper print. \$\endgroup\$ Commented Feb 20, 2020 at 15:45
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As long as you have enough resolution in your printed pattern, it doesn't really matter exactly how far the camera is from the pattern.

For the purposes of example, your question caught me when I was doing laundry, so let's assume I want to reproduce the image on the front of a concert t-shirt at 1:1 print size.

All that is needed is the ability to take two (2) photos of the subject, with the camera in the exact same position relative to the subject. A picture is worth a thousand words; in this case, I need 3 pictures:

  1. The setup. You need to hold your camera at a fixed distance to the subject. Since you are talking about flooring, and you say you're not a photographer, I chose a possible setup you might use: a camera phone taped to a convenient height (such as an end table, chair, etc.), aiming at the subject (floor in your case, t-shirt on the floor in my example):

    enter image description here

  2. Take the picture of the subject. This is what you will eventually print to get a 1:1 print reproduction.

    enter image description here

  3. Take another picture of the subject, but this time, put a ruler or other known reference distance in the image. If you have ever watched police procedural shows such as Law & Order, NCIS, etc. ad nauseum, you'll eventually see a cop-on-the-scene take an ad-hoc crime scene image with a dollar bill or a quarter, because they are known reference sizes. This is what we're doing with this image.

    enter image description here

Now, using any photo editor that can show inch (or cm) rulers, open the 3rd image (the one with the ruler/known reference). Open the rulers in the editing app, and resize the image so that the ruler/known reference in the 3rd image matches the image editor's ruler scale.

Now open the other image (the one without the ruler) in the same image editor. Resize the image to the same amount you resize the ruler-in-frame image. Then print at 100%.

Et voilà, you have a 1:1 print of your floor pattern. Just trim the border off the print, and Bob's your uncle.

Note: if you're even just 5% more clever than I was in my example, you don't need to take 2 images of the subject. If you place the ruler just outside the pattern image you want to print, you can take just 1 photo of the subject-plus-ruler-nearby, open it in the editor, resize, and either crop the ruler in the software, or trim the ruler out of the print with scissors. There ya go, you saved a step over what I suggested. =)

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