How To Test The Sharpness Of Your Lens

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Most often I hear photographers saying “my photographs are not sharp enough.” Are you worried as well?

If yes, I have a simple but most practical solution. And the solution is…first test your lens for sharpness, as there’s a high possibility that your lens is soft.

Most lenses are not very sharp at their widest aperture. Instead, they are sharp when stopped down by 1 stop or sometimes 2 stops. It’s also referred as “Sweet Spot” of a lens.

Now the question is how you will know the sweet spot of your lens. There are 2 ways; one is a hard way, and other is an easy way.

Which one do you want? Of course, an easy one, isn’t it? It’s a no-brainer. The easy way is to check the lens sharpness performance by looking at its MTF (Modulation Transfer Function) chart.

Read how to read MTF charts for Nikon Lenses or how to read MTF charts for Canon Lenses.

The hard way is to test it yourself. It’s not as hard as you might imagine. It takes only a few minutes to test. But the experience can be rewarding.

How to test the Sharpness of a lens. Sharpness test of a lens. Sweet spot of a lens. Nature Photography Tutorials by Prathap.

I would prefer the hard way for a good reason that it gives me a first-hand experience. Instead of depending on someone else’s test results, why not rely on mine. What do you think?

Okay, now that I have convinced you to test the sharpness of your lens (have I?), let me give you a clear-cut guideline to do it.

Sharpness Test

Most lenses give optimal sharpness only when stopped down by 1 stop.

For example A 100-400mm or an 80-400mm lens set at 400mm might give you sharper results at f/8 than at their widest aperture setting of f/5.6. At the widest aperture, these variable aperture zoom lenses yield softer images.

Is it true for all the lenses?

No. All lenses are not made equal. Some lenses might perform very well at maximum aperture settings.  Prime lenses like 300mm f/2.8, 400 f/2.8, 600mm f/4 and so on can produce sharper results at maximum openings. Even then, they seem to produce slightly sharper results when stopped down.

The key here is to find out how much of a difference is it?

If you can quickly deal with the softness (by sharpening it in the post), then it is okay to shoot at the maximum aperture. But, it’s not always the case.

Simple Test To Check The Lens Sharpness

Here’s a simple test. Remember to perform this test with a static subject. That way you can be 100% sure on the results you get.

Follow these steps:

  1. Place your camera and lens setup on a sturdy tripod.
  2. Place an object (like a vase, flower, toy, etc.) at the minimum focusing distance* (MFD) of the lens.
  3. Make sure there is enough light to get a decent shutter speed. At least 1/500th of a second or more is better. The faster, the better.
  4. Make sure that your subject is at least 10 feet (3m) away from the background. The farther it is from the background, the better it is.
  5. Make sure the background is complementing your subject and is clean. You don’t want any distractions. You need a bokeh effect so that sharpness of the subject is easy to recognize.
  6. Set your lens at its maximum aperture.
  7. Put your camera in the live view mode.
  8. Focus perfectly on the subject.
  9. Zoom in to check if it is perfectly in focus.
  10. This is very important. Lock the Focus. Or, switch to Manual Focus so that focus remains the same throughout the experiment.
  11. Use a remote or the timer mode to take a photograph. You could even try using mirror-lockup.
  12. Take a photograph at the maximum aperture setting of the lens.
  13. Stop down the aperture by 1 stop. For instance, if the maximum aperture is f/5.6 then chose f/8.
  14. Take another photograph at this new aperture setting.
  15. Stop down the aperture by 1 more stop. For instance, if the maximum aperture is f/5.6 then choose f/11.
  16. Take another photograph at this new aperture setting.

* Minimum Focusing Distance (MFD) of a lens is the closest subject a lens can focus. This distance is measured from the focal plane in DSLRs, not from the front of the lens. A focal plane is normally denoted by the symbol Φ on the Camera body.

Check The Results On A Laptop/Desktop

Now check these photographs on a big monitor to check the sharpness. The bigger the monitor the best it is. How is the sharpness now? Is it sharp enough at the maximum aperture or when it is stopped down?

If it is not sharp at any setting, there are 2 possibilities. Either you didn’t do it right or the lens is defective. I will hold you responsible! At least for now.

Now go back and perform the same experiment at least 10 times. Perform in different lighting conditions or with a different subject. Try changing the tripod. Make sure the background is too far so that you can get a nice and soft bokeh.

Find Out The Sweet Spot Of Your Lens

The above sharpness test, if performed as per the guidelines, should yield you a clear answer about the sweet spot of your lens. The sweet spot is nothing but an aperture setting at which your lens is sharpest.

How to test the Sharpness of a lens. Sharpness test of a lens. Sweet spot of a lens. Nature Photography Tutorials by Prathap.

Do you get sharp results now? You know which aperture to use? Use it. If the light is extremely poor in the field, go ahead and use the maximum aperture. The point is you should know what to expect.

Some Examples

Remember, prime lenses are often sharp at their maximum aperture. Here are some examples when I have stopped down to get the best sharpness possible.

Bharatpur bird sanctuary or Keoladeo national park. Bharatpur. Rajasthan. Sharpness Test of a Lens. Bird Photography by Prathap.

Nikon D7100, 300mm f/2.8 prime lens @ f/2.8, 1/2000 sec, ISO-100

Bharatpur bird sanctuary or Keoladeo national park. Bharatpur. Rajasthan. Sharpness Test of a Lens. Bird Photography by Prathap.

Nikon D750, Nikon 600mm f/4 + 1.4x teleconverter @ f/8, 1/4000 sec, ISO-1600, -0.3 Ev Step
Note: Maximum Aperture of the lens is f/5.6 due to 1.4x teleconverter. I have stopped it down by 1 stop to increase the sharpness.

Bharatpur bird sanctuary or Keoladeo national park. Bharatpur. Rajasthan. Sharpness Test of a Lens. Bird Photography by Prathap.

Nikon D750, Nikon 600mm f/4 + 2.0x teleconverter @ f/10, 1/1250 sec, ISO-400, -0.3 Ev Step
Note: Maximum Aperture of the lens is f/8 due to 2.0x teleconverter. I have stopped it down by 2/3rd stop to increase the sharpness.

Bharatpur bird sanctuary or Keoladeo national park. Bharatpur. Rajasthan. Sharpness Test of a Lens. Bird Photography by Prathap.

Nikon D750, Nikon 600mm f/4 + 1.4x teleconverter @ f/8, 1/800 sec, ISO-5000, -0.7 Ev Step
Note: Maximum Aperture of the lens is f/5.6 due to 1.4x teleconverter. I have stopped it down by 1 stop to increase the sharpness.

Bharatpur bird sanctuary or Keoladeo national park. Bharatpur. Rajasthan. Sharpness Test of a Lens. Bird Photography by Prathap.

Nikon D750, Nikon 600mm f/4 @ f/4, 1/1000 sec, ISO-560, +0.7 Ev Step

Bharatpur bird sanctuary or Keoladeo national park. Bharatpur. Rajasthan. Sharpness Test of a Lens. Bird Photography by Prathap.

Nikon D750, Nikon 600mm f/4 + 2.0x teleconverter @ f/10, 1/1600 sec, ISO-800, -0.3 Ev Step
Note: Maximum Aperture of the lens is f/8 due to 2.0x teleconverter. I have stopped it down by 2/3rd stop to increase the sharpness.

Bharatpur bird sanctuary or Keoladeo national park. Bharatpur. Rajasthan. Sharpness Test of a Lens. Bird Photography by Prathap.

Nikon D750, Nikon 600mm f/4 + 2.0x teleconverter @ f/11, 1/1600 sec, ISO-800, -0.3 Ev Step
Note: Maximum Aperture of the lens is f/8 due to 2.0x teleconverter. I have stopped it down by 1 stop to increase the sharpness.

Still Soft?

No matter what you do, if your lens is still soft at all the aperture settings, then blame the manufacturer. Get the lens serviced or get it replaced! I would prefer the latter.

Remember…you have paid a huge sum, and you want to get only the best. No two ways about it.

Conclusion

Did you understand how to test the sharpness of your lens? Good.

It’s not enough to understand. Testing it is important. If you don’t test it now, my whole point of writing this article is worthless. You have to take action. Only then I can justify my time and efforts. You have to take responsibility to make my efforts worth.

I hope you would do it. I have faith in you.

Have you done this sharpness test anytime? Let me know the results in your comments.

Talk to you soon.

Cheers,

Prathap

P.S. Did you check the survey results yet? Here it is…


 

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5 Responses to How To Test The Sharpness Of Your Lens

  1. Diane Prather November 20, 2016 at 2:28 am #

    I like the information but I can’t print it so I can try it. Thank anyway

  2. Jimmy Rey December 19, 2016 at 3:04 pm #

    I really appreciate the insight here in this post and confident it’s going to be helpful to me and many others. Thanks for all the useful information

  3. Ian Sempowski March 23, 2017 at 12:09 pm #

    stupid question,
    lets say you have decided that for your nikon 600mm fl F4 lens the sweet spot is around f8.
    now you add a 1.4 TC. i know that now your maximum aperture is 5.6. is the sweet spot now f11 or does it stay at f8?
    Ian

    • Prathap April 6, 2017 at 3:16 pm #

      Hi Ian, that’s a good question. It’s usually true that you have to stop it down by a couple of stops when you use a TC. But, I am not 100% sure if the sweet spot changes linearly or not.

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