Macro Diffraction Calulator

How to use the Macro Diffraction Calculator

As you close the aperture (large f-numbers), depth of field increases. This gives you the power to easily increase depth of field, but with the limitation of diffraction.

At small apertures (f/16, f/22), the rays of light start to interact with the edges of the diaphragm blades, getting dispersed. Light waves start to interact with each other, canceling out in some places and adding in others, causing what is called Diffraction.

Diffraction will reduce the resolution of your images, softening them and making them look less sharp.

Our basic Diffraction Calculator doesn't take into account magnification. Then, it cannot be used to assess diffraction in macro and close-up photography.

Magnification is the proportion between the size of the subject image on the camera sensor and its real size. For example, a magnification of 5:1 (5x) means that the image of the subject is 5 times its real size.

Another new variable that affects diffraction is pupil magnification. This is the result of dividing the diameter of the exit pupil of a lens by its entrance pupil diameter. For focal lengths around 50mm, not taking into account pupil magnification may work pretty well. 

But, when using long focal lengths, such as 105mm or 180mm, you should take into account pupil magnification to get more accurate results.

So, this Macro Diffraction Calculator will help you asses the largest aperture at which you’ll start seeing the image lose resolution. This aperture is called the diffraction limited f-stop.

Therefore, closing the aperture beyond the diffraction limited aperture may cause the effect of diffraction in your images. 

Would you like to see how diffraction looks like? The following image shows the effect of diffraction in a macro shot. Believe it or not, sometimes, diffraction can be used to create beautiful blurred backgrounds.

This calculator takes into account magnification and pupil magnification to give you a good approximation of the diffraction limit values in macro photography. Just introduce camera model, megapixels, aperture, focal length, focus distance, pupil magnification and extension tube (in the case you use one) to calculate:

  • Magnification: The proportion between the size of the subject image on the camera sensor and its real size.
  • Effective aperture: Magnification has the “effect” of closing the aperture. At 1:1 magnification, you lose about 2-stops of light. This means that an aperture of f/2.8 becomes more like f/5.6.
    • This calculator computes effective aperture as: lens aperture × (1+ Magnification). This works pretty well for focal lengths around 50mm.
    • For longer focal lengths (macro lenses), you need to take into account lens Pupil Magnification. Then, effective aperture is: (1+ Magnification/Pupil Magnification).
  • Airy Disk: The diffraction pattern formed when light waves are scattered. The waves start interacting with each other, adding in some places and canceling out in others, creating a pattern.

Regarding the aperture, on the calculator, set "YES" to "Aperture is already an effective f-stop" if you're using a Nikon camera. These cameras automatically correct for the effective f-stop and show it on the LCD display.

Finally, on the one hand, the calculator gives you the aperture that may suffer from diffraction on a 100% Crop (real pixels): 

  • Pixel size: The size of a pixel in your camera.
  • Diffraction Limit: The aperture that may produce diffraction on a 100% crop. In this case, It's assumed that a camera is diffraction limited when the Airy Disk is larger than 2.5 times the Pixel size. 

And, on the other hand, you get the diffraction limit comparing the Airy Disk with the Circle of Confusion (CoC): 

  • Maximum Circle of Confusion: The maximum size that a blur spot, on the image captured by the camera sensor, will be seen as a point in the final image by a viewer for a given viewing conditions (print size, viewing distance and viewer’s visual acuity). For a given sensor size, the circle of confusion is calculated assuming a print size of 8''×10'' (20cm×25cm), a viewing distance of 10" (25cm) and the manufacturers standard visual acuity.
  • Diffraction Limit: The aperture that may produce diffraction on the printed image. In this case, It's assumed that a camera is diffraction limited when the Airy Disk is larger than the Maximum Circle of Confusion. 

Understanding diffraction and depth of field

Interested in learning more about diffraction in macro photography and depth of field? Wanna learn how to shoot for a desired level of depth of field? Take a look at this article:

The Ultimage Guide to Depth of Field (DoF)

Achieving the control over what is in focus and out of focus in your photos is key. This article will help you learn how to shoot deep depth of field to capture even detail in the moon...

... and also how to shoot shallow depth of field to drive the viewer's attention to one determined spot.

Finally, If you're interested in learning how to imagine, plan and shoot the sun, the moon and the Milky Way, take a look at the following How-to articles:

How to embed the Macro Diffraction Limit Calculator on your website

Take the power of PhotoPills’ Macro Diffraction Limit Calculator with you. Just copy the following lines and paste them within the code of your website, right in the place where you want to embed it:

<div id="ppdiffractionmacro"></div>
<script src="http://photopills.com/widgets/ppdiffractionmacro.min.js" async></script>

The code will run asynchronously, without penalizing the loading time of your website.

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