how to calculate amplification ratio in digital.

Discussion in 'Macro' started by lopezjohnston, Mar 13, 2017.

  1. Good evening
    Technical question: I know that I achieve a 1:1 magnification ratio when, in film, the size of the image in the negative (film) is the same as the size of the object in real life. This is either with a macro lens or with extension rings.
    Now, when we work digital where it is impossible to compare the size of the real life object with the size of the image in the "sensor", how do I calculate the amplification ratio?
  2. Why impossible? You can google your sensor's size in mm and pixels. You can count your subject's size in pixels on the screen too (auxillary lines might be helpful) some software (Adobe's?) even does the measuring between 2 points you are clicking.
    Other approach: with focal length and extension / bellows draw known (or measured) and lens focused to (engraved) infinity you could calculate your magnification too. (Adding 0.5 focal length => 1:2 or adding the focal length => 1:1)
    Is knowing magnification really critical for your mission? - As in operating a process camera to gain films for contact copying?
  3. Here's a little help tool from the early Eocene:
  4. Jochen
    Thank you for taking time to reply.!
    When I said "impossible" I was thinking on measuring directly on the sensor as you do on film.! I think it was more a rhetorical expression. I had not considered an indirect way to measure knowing the size of your sensor and extrapolating the proportions to whatever the size of the real subject.
    Part of my photography is scientific and I like to know magnification factors for technical purposes.
    i do appreciate your inputs and time! Best regards.
  5. JDMvW

    Thank you for taking time to reply.
    Those Eocene techniques are always "cool to know". I was not familiar with it, I will study to at least see how the numbers work.

    THank you again and Best Regards
  6. Why don't you use a scale in at least some of your images? That works well for me for images ranging from the outcrop-, hand sample-, to microscopic-scale. My students roll their eyes when they have to serve as walking scale bars (jokes are routinely made concerning the perfect five-foot student). For soil profiles and smaller outcrops I have a dedicated plastic cards (the better ones double as gray cards for color correction), and for microscopy work I use a calibrated slide. That skips over the scale typically encountered in macro photography (my work does not require many images on that scale that cannot be taken with a good scope), but I don't see why it wouldn't work. Photoshop or freeware such as NIH image then does the rest.
  7. Easy if the digital camera and the film camera have the same mount. Mount the lens on the film camera to determine magnification and the put it on the digital to take the pictures. Another way to determine of the size of the image on the sensor is to take a test shot and then count the pixels. If you are scientifically inclined you should be able to figure out the math easy.
    If not tell me which camera you have then I will show you.
  8. Now that I think about it for a few minutes. There are many more ways to determine magnification with a digital then with a film camera.
  9. ".... digital where it is impossible to compare the size of the real life object with the size of the image..."

    You know exactly the size of the sensor which simply means that nothing changes from 35 mm film if you use camera with FF-senor.
    If you use Nikon, Canon, Sony DX (APS-C) or other maller formats cameras and use the same lens you just have to change fron sensor distance accordingly to get 1:1 magnification.

    See sensor details Diagonal (mm) Width (mm) Height (mm) Area (mm²) Stops (area) Crop factor here:
  10. Lifesize or 1:1 is always lifesize, whether the image is projected onto a piece of film or a digital sensor of any size. In fact any scale of magnification stays the same regardless of format size. The format size simply dictates the angle, or field, of view.

    What happens after the image is taken is irrelevent. It can be enlarged, by projection or digitally, to any size you like. The in-camera image magnification is what's taken to be the magnification ratio, de facto.

    m=v/u or m=image-height/object-height. Those formulae hold no matter what focal length of lens or what size or type of camera is used.
    Last edited: Mar 21, 2017 at 5:36 PM
  11. BTW. Amplification isn't the correct term to use either. Amplification occurs during the chemical development or electronic processing of an invisible latent image.

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